v

-1

Write.o copior for eoch poir of oloros, explo nirghow the phoos ore linked

* Think of onofru poir of photos thd rould be oddedto these lwo.

ilt!+

1r!!+

Pz

(rnsEach of the three structures on the previouspage is made of small building blocks. Thebuilding blocks of living rhings are called celis.

All organisms are made of cells. Your bodycontains over 3 billion cells. Most cel)s are ve4.smail and can be seen only lvith a microscope.Ho,,vever some cells are large enough to be,eLn !tiIh voLre)e. forexrmple. oird. egg.are single ce11s. The emu egg is the largestsingle cell of alll

Some organisms consist of only one cell.These single cells are complete organisms andca.l li\ e 'ndependen' y lrom olher orguni.ms.The photo below shows single-celled organ-isms called euglena (you-GLEEN-a) which livein fresh warer and contain chlorophyll to maketheir own food.

Fig 3 Eugleno ore singh-celled orgonins thot live inheshmter lokes ond ponos liny hois ot one end ol the rcllhelp lhen swin through the woter.

Large organisms contain many differenttypes of cells and each type of cell is special-ised. This means thar each type of cell wo.ks i,ru different way. For example, in the humanhody. red blood cells carry oxygen, muscle.ells contract and relax to move bones andorgans. nerve cells conduct nerve messages,and stomach lining cells make substancesuhich help in the digestion of foods.

Fig 4 Red blood celh ore speciolised cells which corry oxygenoround yaur body.

Fig 5llerve celb hove on irregulor shape.lhey corry nervenessoges lhroughout your body.

The photos of the ceJls on this page arernany times larger than the actual size ofthe cells. Each photo shows the numberof times that the cell has been magnified.For example, the x'l50 on the euglenaphoto means that the cells have beenTagni'ied 150 r Tles. You can use thisiniormation to iind the actual size olcells.

l,4easure one of the Euglena cells withyour ruler. Then divide thls by 150 (themagniiication) and give your answer inmillimetres.

! Find the sizes oi the olherlphotos.[_

celrs jn the E

o"3I

Lefit E!s5$e5 ol1d 0rg0lr5The celis of single-celled organisms such aseuglena can exist on their orvn and are calledindependent. However the cells in large organ-isms are generally specialised and thereforecannot exist on thek own for very Iong. Forexample, a single cheek cell wili die afrer ashofi time outside the body.

Celis of the same type are generally foundtogether. A group of similar cells is called atissue. A tissue is a group ofcells organised todo a particularjob in rhe body. For exhmple,the muscle tissue that lines your stomach andEul j5 made lrom muscle cells. The.terve lissue -in the brain and spinal cord is made from ne ece11s,

=.'&mlac e tibate

lo ,Nau-th

connea-,iveLlgaue

P.+Ce!Is

Living things are called organisms. They come in a variety ofshapes and sizes and.can generally be classilied as either plants or aBimels. Living organisn:s are made upof tiny living parts called cel/s. Some iiving things corsist of only one cetl, whileother plants and animals contain millions of cells. Cells are the rnits fiom whichliving things are built, rather Iike houses built ofbricks. This is why cells are oftenreGrred to as the building blocks cf living things. This means that you, a iree, aninsect, and a bird are all made up of cells. All cells live, grow, and eventually die.SIZES OF CELLSMost cells are between 10 and 100 microns across. (One micron is equal to onemillionth of a metre.) Thus we must use a microscope to see them. Yout bodycontains about 50,000,000,000,000 ce1ls: one drop ofblood contains over a millionred blood cells. On the other hand, some liying organisms, such as the amoeba,consist of only one cell.SOME TYPES OF CELLSDillbrent living organisms are made up of different cells. Somg cells are long andflat, while othe$ ar€ rounder. Cells with different shapes have different functions.Some cells of differing shapes are shown below.

I!J1l[,:::ii:i:'] I

I l,@ril1----11

Boot tip cell

/.-- '\ ,4F''hqsl \n/

Red blood cells

\\-_,,",

---.,/ffi,"","",,\tL.,;")li{(

It is important to realize that cells are 3dimensional obiects. Diagrams show onlytwo dimensions and can give a false impression. Individuai celis tend to be sphericalin shape; cells touching each other are more box.shaped.

Cells having the same firnction aad similar size and shape, group iogether to torm,tsszes. Nerye celis, for example, group together to form nerve tissue. Differenttissues can group togethe! to fotm organs, Some of the organs of the human bodya!e: the heart, stomach, brain, and iungs. Organs group together to form bodyststems, e.g. the digestive system in the human body"

Spernr cell

Nerve cell

Smobth muscle cells

CELLS* TISSUES.- OR.GANS- BODY SYSTEMS

P.c

Copy and eomplete . . .1. .All organisms are composed oftiny liviag parts ealled2, Cells usually camot be seen with the unaided eye, but can be seen with a

3. Most cells range in size ftom 10 to 100

-

ecross.4. The number of red blood cells in a drop of blood is about _.5, ?lant aad animal cells are _ in size a,nd sbape.6. Ceils are actually _ dimensional in shape.7. Groups of similar cells clumo tosether to form8. Tissues can group together to form _.9.

-

can group together to form body systems.

Examples oi cell diagrams

ACTIVITY; CELLS LI}IDER A A,IICROSCOPEa. Take a razor blade aad cut a very thin slice ofonion skin frorn between the lavers

of an onion, Place the slice on a microscope siide and examine the cells. Add adrop ofmerhyiene biue stain to the slice. Can you see the cells more easiiy? Drawa group of 5 cells. Tate care to record detai!.

b, Obta.in some prepared microscope slides ofvarious types ofcells, and study themunder a microscope. Sketch a group offive ceils from each specimen, Observe thedifferences between rhe cells.

D,L

qlrr rHu(t)sE5A living cell is constantly active. Substancespass into and out of the cell through the cellwall or cell membrane. Chemical reactionsoccur in which large molecules are brokendown to small ones and small molecules arebuilt up to iarger ones. For example, mosl ofthe matter in the cytoplasm of a cell is made ofproLein. During cell di\ ision. the exl-a prole;nneeded for the new cell is built up from smalleramino acid molecules that pass into lhe cellfrom the blood or the liquid around the cell.

Let! reSprrott0nThe cells in )orr ood] ma) haue ro perfonlmany of the follo1,ing functions.

. Muscle cel1s callse mar)ement., All cells make prcreirs (eg enzymes) and

other large molecules.

" Nerve cells .terd rerve impulses.. Many rypes ofcells divide.All of these functions require energy. and

the cell's maifl source of energy is glucose. InChdprer I )ou leamr rhd! cell rc.piral:on i< anexotheamic reaction-it releases energy. r&ten

glucose is broken down, oxygen is used andcarbon dioxide, water ard energy are p.oduced.

glqcose + oxyle^ *carb.^ dioiAe + vet?i t eA.JAl

This energy is used for muscle movementand nen e trJn:m:55ion, and in endorhermicaeactions where large molecules such asproteins are made frcm smaller molecules.

Cell respiration occurs in organelles calledmitochondria (might oh-KoN-dree-a). Thesetiny organelies vary in shape from round tosausage-shaped. depending on the type of cell.and are found in all cells that contain a nucieus-The number of mitochondda in a cell indicatesits energy requirement. For example, musclecells contain up to 5000 mirochondria, while acell in the skin may have fewer than 100.

Energy for mus(!e movemenfSkeletal muscle is the type of muscle thalmoves bones. It is also called stdated musclebecause of its striped appearance under themicroscope. The other types ofmuscles in lhebody are hean muscle which is found only inthe heart. and smooth muscle which is found inorgan5 such a) lhe qiomach and inlectine.

ENER6Y USED FOR

mavelfenl

resfiratiog'a

6ell divliioh

fiaking laqe

o*lqen

Fig l5 A tell pelorns o nunbu of fuattions in the body- ldoay of lhese funclions rcquire eaetgy.

?.7Obtain two 100 ml conical flasks. AdC one teaspoonF,:i of dry cor::pressed yeast to

each. Add 50 ml of warm water to each. To oze of the fiasks, add orr. ta"rpoon "f'giucodin' - a suga!. Shake well. Ligkt$ stoppet each flask. Alto*- rh. anrt, to

stand in a warm wat bath at 35.C for one hour. i".pe"t fr.qoerrtiy.-

!i,aim vr'aief b6ilr

The energy is used for livins.Cells need energy for:

growthieproductionother functions

Flartt cells make their own food,Animal cells usually receive food fromthe bioodstream.

veesi ^:taf + yEasl + guccdn

It,mav take up ro an hour for rhe yeast ceirs to become active. In wfuch flask do thecelis becoae active? What evidence is thele to suggest ihat carbon dicxide gas isbeing produced? \Wlat couditions are necessary foi veast cells to become active?-What other tesrs could you conducr in order :o be su:e?WHAT CELLS NEED TO SURVIVECells cannot fuqction without Ibod ald warer, and thev also needtemperarure" lf the temperarure fblls below 0oC, then ceils ceasebecause the waier in them freezes.

Respiratioe. is parr ol a cell,s activity. Respiratioe occu,-s in all living ceiis. ;rinvoives the 'burning,offood with oxygen to prod,rce energy. Carboll dioxide anduater are also produced.FOOD + OXYGEN ._ ENERGY + CARBON DiOXigE + Y/ATER

OxygEn r. F.oC n lsu9a')

CO, oui Water out

the correctfunctionirg

F,8

Copy and compleie . . .34. The activity of a cell is called its _.35. In order to survive, cells need a conrinuous suppiy of_ and36. Celis obtain energy by a process called37. food + oxygen -38. Plant cells

-

their oifir food. Animal cells receive food through the

Drrrusron tru

r

a.qI

DIFFUSION THFOUGH A I,,4EI\IBRANESome substances seem to be able to move in and outof. cells rhroJCh the nembr"1e5 _fairt, eas;l). Orhersub.ra'rcei ei.her ca-1or pass rh-ouPh ihe membrane,at aTl or do so onty sto\rly.

. Any. membrane that allows some substan€es !o passthrough it more readily than others is called a df-lerent iaLly -permeabte m.mbrane _

PurposeTo investigare the acdon of a differentially permeablerre..brane.

Conrinue urtil the bag is iull and the slarch isabour 2cm inro rhe Sorron of rhe gjas! tube ofIhe ihisrle funnel

Add water to rhe giass jar unril it is about 1 cmabove the rop of ihe bag. Add iodine solutjon untilthe water is a distinct yello\r'ish colour.

G Mark the level of rhe starch in the glass tube.Label lhe second appamrus .8, and set up in thesame way bur with glucose soluliol1 inslead ofstarch and with no iodine.

Dip a piece of Testape in the rvater and reccrcl thecolour.

MatenaLs and Lquipment(per pair of students)1. Cellulose rubing, 20 cm lengths, 22. Thisde funnel, 23. Soluble starch solution4. Rubber bands, 25. Glucose solulion6. lodine solurion-. Sknd with clamp (lo )upporr rfu.lte fun-

net),28. Gas jar or similar talt slim container, 29. Glass-marking pencil or felt-lipped pen

10. Tes-iape11. Rule graduated in mm

Prseedurec S-ei

-up two sels of appamlus as sho\r,n in Figure

10a.3-1, one wirh slarch and one with etucosesolrr'on,

\orp(r The ..e uto.e rrbi.rg ray be opened b\morsten'ng L and rhen rubbing berseen fir!er andIhumb.

Tie the bottom knor about 1cm from the end ofthe tube.

Be careful nor to damage the tube.

Put rhe end of lhe thisrle funnel about 6 cm downinro lhe upper end of the cellulose rubing andfasten tiehrly *irh a rubber band.

c M.rk one ser ol aopa-orus .A. and pou- .tarchsotJlror rnro rhe rhisLle fL'1nel u,Iil !J.e lop ol .nefunnei is abour half futt.

e Squeez. rhe bat ge-rt) ro help -he sra-ch ro rore

Frgure 10a 3-l

A1low the two seaups ro sland for between 30minutes and one hour.

Observe the level of starch solurion in lhe rube inExperiment A, measu.ing and recording anych,nge thar ma)'a\e laLen p,ace. Record ar\coroLr cha-ge observed eirher jr rhe b"g or:n rh;u'ater in lhe jar.

Observe the level of giucose solution in the rubein Exledment B, again measuring and recordin8any charge. Djp a prece of Testape i.ro rhe sare;ir ihe jd,. Record ir. colo,r- ano lhe plrco.econcenrration lwn,ch )ou can -edo f-olr Lhe-coloLrchart).

P,t0

3 Let both selups stand overnight in a safe place'

e The next day again measure the levels in bothrhisrle funnel tubes. noling !he colours of thesolutions in Experiment A and lhe concentrationof glucose in jar B.

Oue.tion rlt. Slmmarize your ob5(rvalion' of Iheerpirim.nL using slarLn soluliol' Que5Iion l2' Sum-marize your observations of the experimenl using glu_cose solution.

Strldying the Data

OJestion r3l. f rom your experirnerral resulLs and fronv-our knowJedee of ll'e chemicottest for slarch' wharl,ust hare iappened to the iodine molecules inF,'oerimenl a? Oueslion (4,. v'hl:h materjal did notpass rhrough a minbrane? Hou do )ou kno!":

Question (5). From your experimental reslllts, \"'hatmust have happened to the glucose molecules inExperimenl B? Question (6) From the evidenceobtained by aliowing Experiment B to stand overnight,what othei subslance must have passed through themembrane? How do You kno$?

Conclusions

Ph-vsicisls can measure the sizes ot molecules byvarious methods. They have shown ihat iodine mole_cules and waler molecules are very small, glucosemolecules are considerably larger, and starch molecules{which are svnrhesized from many glucose molecules)are very large. Quesljon (7) Using this infcrmation asa basii, suggest a hypothesjs to account for iheobservations made in ihis exercise.

The cells making up the bodjes of iiving thingscontain soluiions in which lhere are large molecules notcapable of passing through the membrane. Yet walermolecules can pass freeiy through lhe membranes oftiving cells. Quesrion (8). Predict what you \!ouldexpect to happen !o such a cell if ir were placed inPUre waler,

For Further investigation

Suppose you we.e to paldy filI a cellulose bag wirb asucrose (cane sugar) solution in much the same \,, avas above, then withdrew lhe thislle funnel, tied the endtightly and put the resulting sausagelike 'orBanism'into waler. Question (9). What would you expec! 10happen? Test your predjction by pedorming theexperiment.

p. lLJ

GRowrn nluo REpRoDucTsot*When a bean seed is planted in moist soil, therocts begin to grow and become larger andionger This giowth occurs because the roorsmake more celis. This is done by a processcalleci cell division. The ceiis in rhe areajusibehind ilre tip ofthe roor divide in rwo. Asmore and more cells are produced rhe bean roo!giows longer.

Producing liew lifeAll organisms reproduce to make more of theirown kind. Single-celled organisms do this bycell division. They simply split ir two roproduce offspring which are identical to theoriginal organism. This is ofien called asexualreproduction.

Fig 2A Micrwapk orgonisms reuodwe by splitting ir twa.

Larger organisms reproduce seruall). To dothis. Lhe fwo parenrs , one rrale and ihe otherfemaie) produce sex celis. ?hese celis ilredifferent from the other celis in ibe bodv. Thevcan combine to make one new cell whi;h the;i_econes a nerr and indepenienr orgonis--r.

The maie sex cell is called a sperra €eXl.These sperar cells are ver$malj eells and areproduced in huge quantities by rhe male. Thefemaie sex cell is called an ovurn or egg cei]and is much larger than a spenn cell. (Theplural of ovum is ova.)

When a sperm and ovun1 meet, the nijciei ofthe two sex cells join together and a new livingthing is formed. This pro.ess is called fertilisa.tion (FUR-ti1-eye-ZAY-shun).

Fenilisado r can occur exremallJ. or iater-na1ly. For example, in humans the male depos-its the spem inside the femaie's body andfefiiiisatiot occuN intemaily. In frogs andsome fish, the iemale releases her eggs in thewater a4d the spelm, released by the male.swim to the eggs to fefiiiise ihem extemally.

aata fierkea at.equa) inlervala

qrar.thaccurahere

tv/o Aa:j.lai.t

Fig !9lhkhean raot hosbeen notked at er,uolinarvlls.lwl days lotet lhe da!neu the roat tb ore nuth lurlheropoti hecause new rclls were forneC iere.

Ail li\ ing lhino: dro!, by mdking ne\r cell..YoJr body grou s rapidt) in sragec up ro rheage oi about 15. During this time your bonesgrow thicker and longer. For example, yourLiieh bone , femur gro$ < rc abou! i Ii-ne, rt.length at birrh. Cells behind the head of rhebone divide to make new celis.

Your skin grows in much the same way.Cenai'1 cells belou fie slrface oI the skindivide to make new ceils. So as the bones andother parts of your body grow larger your skinalso grows. However. unlike bones which stopSrr ain! ar adJlrhood, ce.r oivisjon conli-lLe:in the skin until death. The skin conrinuallyIos:( cells lrom its sJfoce. and ro replace *re(ecells nevl ones are made.i

P"12

tio 2l Hunor' sletff cels (v40a0.lhehunon spern rclloiks ljke o niniature ndpote . I utes its llil la lv,in thrc'rghliquld. The heod ol the spern tanloins lhe nucleus ond s snoll

anounl of cylaplosn.

The sex cells of organisms a.e not a1l the

same size and shape. Fig 23 sho\\'s the actual

siz

v

q)

€i

GI

\

*

mLVJ

*lai@!t@J

o'd[ Yl=o o

Y =a ;nO;E E OJ99

o

op]JoO

q,

alJ

F

.9

o-q !)o

=!- =o

=

'6-.-p

d; e

^qo

D'l+I

Lell d!v!srollIn Chaprer 12 you leamt lhat rhe cells in thegrowing region of the slem and roots of a plantdivide to make new cells. In this way the planlbecomes larger. All muiticellular organismsrely on ceil division for growth. For single-celled orgari.m, -uch a) prorl\t5 and blcleria.cell division is the method of reproduction.

Cell division also occuls when wom out ordead cells are replaced in the body. For exam-ple. in humans dead skin cells are lost everyda1. Those cells are replaced by new ce11sproduced by cell division at ihe botton oi theepidermis. The replacement of cells also occursin the lining of the intestines, the liver and evenin bones.

Flow eell division occurs

The photo belou shows dividing cells in ayoung fish. [n some ofthe cells sausage-shapedobjects have become visible in the nucleus.These objects are called chromosomes(KROME-oh-somes).

ilg 6 Dtvtdtng Ce s ttt 0 Y1Ung nsfi-

Chromosomes carr) the genetic code for anorganism. It is lhis genetic code which deter-mines the features and characteristics of yourbody. In humans 46 chrcmosomes ca.ry lhege4e.r for all the human characterislics: forexample. the colour of your eves, hail and skin,the general shape of your body and the \r'ayyour organs and systems operale.

The series ofpholos belolrrhowsa wheatcell dividing inlo two- The chromosomes havebecome visible in the second photo-

\-

\'

Tq

r!ClL!!l

Ti

o

oI

I

Deaa aell, areaot lrafi l,hetkin'.61)*aae.

llew cells aremaae in taloqrcv/ n4 reqion.

i)lr.

FiE 7 Gll divbion accurs in lhe skin. New celk ore node otthe botton of the epidermis to reploce the deod ones lut lron

the surtoce of the skin.

A wheat ceLl. The

rounded nucleus can

be seen in thec!'toplasm.

The chromosomes

can be seen. Celldivision begins.

The chromosomes

duplicale and each

A cell wall growsbelween the two nucleiand lhe two cells

separate.

--, ,,

P. ls

when a cel. i' nol ir Lne Proceis ofdividingthe chromosomes ca,.lnot be seen wilh ordinarymicroscopes because they are long and fiin andtightly coiied up inside tbe nucleus.

In rhe rhird phoio lhe chomosomes have

duplicated and each set has separated. Aflerlhis a cell E'al] grows belween the lwo sels ofchiomosomes. In this way rhe original cell hasdivided !o b€come two cells.

In lhe activity below you wili obse.r'echomosomes in cells undergoing cell division.

(sneer-uncontrolled ceil divisionCeIl division is usualiy an orderly prccesswhich occLrs in special growth reg:ons of lhebody o. i. regions such as the skin tha! special-ice ir c-'" replrcemenr, -n cance_. ho" ever. tlisorderly process goes wrong. Cancer occurswhen certain cel1s divide mpidly and unconlrol-.ably. The cancer cell. ook differenr from lheno.mal ceils in rhe area and rhey do not func-lion like normal cells. For example, in iivercancer. cance- cell. erow rapidll and replacenodnal live! celIs. Graduauy the tiver loses i!siunction and death usually occurs.

Cancer is not a single disease. It can affecldifferent cetls in different lissues or organs ofthe body. But in all cancers, you will onlynotice rhe effects when a growth or s\rellingcaused bi !h. LrnconBol.ed cel d vLion inre-feres \1ith rhe normal working ofthe lissue orcrgan. For example. in Jung caacer the cellsfoml a groqlh qhicn (au,es . pe-"i.ten[ coug\.the splitting up ofblood and shoftness ofbrealh. The cancerous grcwth usually starts inihe cells in lhe walls ofthe bronchioles. Theselubes ca.ry air !o and from the lungs. Theg.owth spreads th.oughout th€ lungs andeventually stops the funcrion of lhe lungs.

Fig 1 I Bronchiol* ore snoll oir lubes in the lungs. Lungconcer usuolly arcurs in the bromhiolet.

Ofall cancen, Iung cancar is the mostcommon. It is responsible for abour 570 ofalldearhs from drsease in Australia. ft is also atype ofcancer ihar is very ha.d io curc, mainlybecause the growlhs become }!ell esrablishedlhroughoLrt the lungs before they arc delected.Mosr people diagnosed with lul1g cancer have ave.y small cha.ce of full.ecovery' Lung cancer is caused by caoceFfo.mingchemicals c alled .a/rirogear (car-SL\-oh-gen.i in cigaJerr: (mo\e and pollrted Eir. Ourof ten dearhs due to lung cancei in Australiathis year. nine of those people will be smokers.The carcinogens in rhe air iIrilale rhe cells inthe walls ofrhe bronchioles. and &e cells maythen staft diriding unconrrollabll. Ofnon-smokers. more dearhs occur in people who livein cities then ihose who live in rhe country.

Lung cancer is especially dangerous be-cause the cancerous celis can spread to otherpafts ofthe body. The lung rissue contains a lotcf blood vessels, and ifcancerous cells get intolhe blood they can be carled to olher tissues ororgans such as bones, brain or stomach i,herethey can folm fufther cancers

in a h.elrhy b.onchiole, the basalcells divide from rime !o rime !oreplace the cells above them whichhrve become damaged and &e nolonge. ol use ro the body.

Pollued ak or air conlainingcigarefte s6oke causes rhe tiningcells io mlke more mucus.lvlo.eof thes. celh ee damaged, so fiebasrlcells divid. ro replace rhem

Celldivision in rhe bNalcells niybe.ofte unconrrolled. A cancerous

Sroslh lonns. causins a s\eellingin the bronchioles. Ca.cerous cellsmat also pass into rhe blood.

(wi.a?Ve)

1 Tony observed some ieaf cells under amjcroscope. He rhen sketched and iabelledone cell. Some of his labels are incorrect.Draw the cell in ) our notebook and label ircorrectly.

P. lb

vacuo)e cdl menb(ane cjtaalagm

organel)e ntcleug

What are chromosomes? Are they norrnallyvisibie in a cell? When can you see them?Suggest why 15q incidence oi Iung cancer islower in people q,ho jive in the counlry thanin those who live in cities.l- which pan, oi r oul body wouldcelidivisicn be occuning at this moment?Would cell division be occurring in an 80year old person? Expiain.'Why are most cancers such as lung andstomach cancer detected more in oiderpeople than in young people?

The rable below shows lhe d:aLhs o-e tLrvarious cance$ in Ausfalia in 199.1.

\n 1994,122192 people died from diseasesin Australia.(a) How rnany died from lung, skin and

stomach cancers in i 994?' b'\ Ol rhe people u ho d:ed from oiseases in

199.1, whar percentage died from lungcancer? What percentage were malesand what percentage were females?

(c) Suggest why lung cancer dearhs are sohigh.

(d) Suggest why the rumber of deaths dueto Iung cancer is much greater in malesthan in females.

(e) What is passive smoking? Why is itdangerous?

cancer

stoinach

l GENEIICSI'leiesis (sex cett

Singie-gene inheritance

A. Body cettfronr indiyiduaty.ith genetic Ineka-up ,AA,

* ru.r

(e)

t Y:::j,:fil .O - a guide, complete diagram B above showing the sex cells produced 6om an indilidual oi

Two-gene inheritance

A. Sody .etlfrom indjviduat with g. in dividu a ( genotyp€ 'AeB b, e. Indjvidual genotlFe 'AaBb,

LinkedLirkgd

genotype'AABB,

/rrGr( l'f' )

+

/i$il+A

Usrng dragram .A a: a gurde, complere diagmm B to shou,the variety ofsex cells produced by individual'AaEb. a.s.:mrng Iinked genes *.ithout ciossing o,er.

Complere diagram C to show the variety ofsex cells produced from the same individual ,AaBb,_ rhis timea".umrni hnkeo genes s.irh crossing over:akin; plaie.

?.1'1

formation) aE!d genetics

B. (a)

'"-IETBI

.,1i\ .,-;i\r t8 \r lb \\.1__,/ \! _//

S* c€lE

1 ET6 I

/vt,,';i\ /-,i\U/'- t- rll'A8'

z-nr\ 7i;XJ B'a I f +b\IqyzUUT'U

3 crossnor),\_-zrlf),Y/oooo

F'xs

ll'HO MIGHT HAVE DISCOVER:D IT?Tn?n thde is the quertion, bhat wo tt haoe heppened if WakonEnd t hld n i put loruad the DNA ,t uctule? Thk k "ify' hk-tory which I *f, tald is tu! it goad lepute ailh hislatintu, thoughif E historiqn ca nat gi,e pla$ible ansudt tr s,ch quertions I dorct se? ahat hisbncal Analysis is sboat. y wlt'on nLd ben ki ed4 r tdnis bill l an redsonably su/e I ao"ld nat hqo. soloed the3a,ttu/e alone, brt oho bould? Olby has recettly addrexed hin-!]f ta this q,estian. Wdtson and I oluay, tharyht th"! Liaus Paul.irS @ould be ba nd la haoe another shot ot the si ct|re onc. h,had xen the Ki g\ Co\ege z.nv ddta, but he hds rccntty statedihnt enen though he inhediqt.lr liked o,r ,tl".turc it toak hin aLitie tine la deeide lndlly that his aun bqs ubng- Witho t ortrudel h, tuisht keoer hare done sa. Rcrdtind rruhklin l@as antyhtu ttept auay lron thc salttion. Sh needed to /eqlise that the taa&nias n*i ry ifl oppasit. dircctians and that fue bds6, in theitiatrtt tautotuetn lornLt, bere paired togethn. ,he bas, houeaer,cn the point alleadng King s Call?se and DNA, to @o* ituteadon TMv Ltoba.rc rusan airusl aith BenoL Mauna Wilki shRd announed ta

"s, j,st bet'ote b kne1, ol a\r stru.ture, thst h!

was Sakg b @atk l"ll tirv an the ro m. Au percirtent prcpa-sanda lot adel buildins had aka had ih ef{t (@e had prnioud!icni the aur j;gs t0 buitd itodels but th.y hnd ftot used rhe'r.) and]i prcposed ta Sioe it a tr!- I datbt nrfll ahcthet the discooer! alihe si"eture cauid kaae been delayeA fu/ daft than hta or three

l-hde n a rure Sewnl arsh mt, hoatuer, recently proposed byGunthn Stent and ssppDfted W s ch a ,ophirtieated thinker as Me-dawar. This is that ;f lNatson and I had n0! tiis.ooered the ,buc-iure, in'tuad ol beins teoealed with a llaurkh it ao'td hdo. inkiedatt qfld tlet it, itupaet uould hiae ben far lesr. Fot !hi, sati ofreasofl St.ni hqd aryled that d scientifrc dis.aor! is nor. qkin to otntk oi e.i than i gn..dllr adnitla- S-r.? he a,SL?s isasit.

I m aat aapletply rcncir.ed b! hir i"s,nent- d. )tu, h thi,t6e. Rether than beliw thc! Wdiron aid Cri.k nade the DNAshattn. I @o"ld ratht stress th|t the sndne tua!1e Walson andCrnk- Afk/ dU, I bas olnost loto\ly unknorln at the tine nndWatsot was regarded, in nost cir.L5, ns too brbht to be rentl-vta nd. But @ha! I lhink is ondlook,d in sllh alsufl1?fltt it the ia.ninsn beauty ol ttu DNA da,bb h,lix. lt G the tuale. e @hnhhqs sbrle, q k a, dsch as ,ci tistt. The gmetie eode :@as nat re.

Wat,an left) a\d Criek in re53 withone of thei nodels ol DNA. Dt,tA,lou kno@, i' Midas' sald," saidMawke Wilkins, uith whom theyshaftd the Nobel Prize. "Eperuou whoiorehes it gaes nad."

aeakd all in of,e sa but ii did rct lalkfot iftpac! an e ;! idd beenli?ced togetheL I doabt if it nede all tha! difeftnce that it Dqs Ca-lffibrs oha d;,eoaned Anetica. \Mot ftdttered n,ch norc ardsthat peayle dnd non r |Dft s1o;ldble ta erploit the di.rco?ry uhenit @os ade. It ir thi, *p.t! of the histary of the DNA sn,.tutewhnh I thinlr dqndnds attntian, rilh* than the penonat elm.nt'in the a af discar?rr, hotufter inteBtiry they nar be

", an abje.t

lessan (saad ot bad) to othn @arkerc.Fanck Cnck. "The Daubl. Heli! A Perconl Vieo, 'Nature, rrl.246, page, 766-769, 1974.

P.19

Tabie 14-1 Conposition of DNA in Seve.al Species

Human beingOx

E- toli

30.4%

29.429.7

26.1

24.7

32.E

79.6%27.220.8

26.4\7.7

79.9%21.2

zo.422.725.717.3

3A_1%

24.7

29.1

27.4

32.1

TFIE WATSON-CRICK MODEL

ln the early 1950s, a young Amedcan scientisl James Watson, went ro dmbridge,England, on a research fellowship to study prcblems ofmolecular skucture. T:here,at ihe CnvendGh Laboraiory, he mei physicist FIancis Crick. Both were interestedin DNA, and they soon began to work iogether to solve the problem of its molec-ular struclure. They did not do expe ments in the usual sense but rather under-took to examine all the data about DNA and to ahempt io unifv them into 2meaningful whole.

The Known DataBy LI-e time W:aon anC Cricl beg:n their sn:dies quire a Iot o! irLlormation on rhesubject had alread), accumulated:

1. The DNA moleclle was kno}\[t io be very 1ar8e, and also very long and thin,and to be composed oFnucleoiides containmg the nihrogenous bases adenine,guanine, thlanine, and c,),iosine.

2. According tb L€v;ne's irterpretaiion of his dai4 these nucleotides were as-semblPd rn reperSnt uniG of tour.

3. Linus Pauling in 1950, had shown that a protein's component chains ofamino acids are often ananged in the shape of a helix and arc held in thatforrn by hvdrogen bonds between successive tums cf the he1ix. Pauling hadsuggested that ihe sh'ucture of DNA nlght be similar.

4. X-ray dif{raction shrdies of D\!A (Figure 1a-8) from the laboratories ofMaurice Wilkiru a]ld Rosalind Erankl-in ai King's College, Londory showedma:rkings that almost certainly reflected the turns of a giani helir. (NeitherLnia nor Par'rling was permitied to visit England at that time and so did notsee the x-ray diffraction phoiographs. The Mccarthy era kept ihese Ei,owiiiout passporls. Ii has been suggested Lhai the U.5. Passport Office mayhave determined the wimers in the lace for the double helix.)

5. ALo crucial (ere lhe drr. or ChaJgaff indicarin& as you perhaps noiired inTable 14-1, that (wilhin experimental error) the amount of adenine is thesame as tie amount of dlymine, and the amount of guanine is ihe same as theamou]li of cltosine: A = Tand G = C.

14-AX-ray difraction phato{aph of DNAtaken by Roselind Franklin. The reflu-iicns crossiry in the nidtlb indnatu thatthe mahlule n a l1eli. The heaoy darlctrgiont at lh? lot and bottam are d,te tothe doxly slacked bases perpendiculqr tothe aris of the helix.

.i^tf'

F.2a

T.L

-a-J,"4--,-+l

The double-sLratded het;cnl sfrv.clure of

uNl1, a5 lf9t preselteq tn t9tJ ovWatlon afid Cii.k. The fr\fieuatk oflhe l,elir is compased of the sugatPhos'phale ai.ils ol te atcleotides. Tht rungsare lotmed by lhe fout nilro4eflous hdsesadetike and gaanine (the purius) andtfumine and cytosine (fhe pytinidines).

Each rtag ofisists of tao boies. Xhowl-edge of the disla4ces hetween lhe aflfts,determined from tra'l diffracLion pittures, lbis cracidl in cttablisltittg lheshucture of the DNA molec e.

P.ZL

"V/ho Mieht llave Discovered It?,,

Comprehension Questions.

Qi) Narne some otirer scientists who were working on tire DNA structure problem.

Q2;1a; Whar is a heiir?. (b) Wrat is a doubie helix? (Use a dictionary for the definitions)

Q3) (a) \tr4rat was the 'Kings College X-ray data"?(b) Wlo developed lhe x-raj datal

Q4) (a) What did Linus Pauling suggest about the stmcture of DNA, after iris discoveryin i9i0"

(b) ffiy drdn't he get to see the "Kings College X-ray data,,?

Q5) What does "tauto leric" ulean? (tlse a Crctionary)

Q6) \[hy didn't Linus Pau.ling immeiiiately agree that the Watso( a d Crick rnodei ofDNA was right?

. Q7) What did Waison and Crick do that Maurice Wilkins and others had not tried?Q8) (a) Wtiat do you tirink Crick meant w.hen he said, "R.ather than believe that Watsorand Crick made the DNA structure, I would ratirer stress that the structu.e made Watsonand Crick"?

(b) Hcw is tliis different to \a,hat Stent said?

Q9) What kind ofirnpact did the discovery ofthe strrcture ofDNA lrave orrsociety?(What do 1,ou think we can do now that we couldn,t do before?)

Qi0) What aspect ofthe historl, oithe DNA stmcture does Crick believe detrandattention?

DNA r'--Mend€l esBblished genes as lhe basic D-q,ils of hcredity .

_ ve low krow ilar drc priEary gElericInJormsuon is caried by DNA deoxyribose Eucteic acid).In rlc ,ucl€us of eucafodc cels DNA is coEpleled wir!

pmlciE to folro rhe chroEosoEcs. Th. basic sEuc re ofDNA i5 oudiEcd LcIe rloEg wjrh a.E crplsnatioE of DNArepLcaLioE, The w?y i! which rtre Eessage is tlalIsxojlrcd..

DNA is a arse rnotecule which co.tains irs i.to...aron in rh€, ,r,ruo"," ururr*r^iiiliJiEE Giiis3ecr, c seqLer ce o, o.oe. o, s-ornils \I,Jr,cr are not ioenricaiT re, oas c s roJl:k o' r"€ D.r,. noJecr,re a,-e tie'nrc.eort.es, n D'A ttF? F. t* d{tda b*r;i,",1:;:::,:::;"'::::j:;191';'--oi*-e1a!"q.,n a"di c

- r^\-- a* t** A^.d onGDnE'e g.oJD, aoo a C _ ,^\ _ _ Ada* .4^lroge. corla,nrng orgar.c base. Tne sroar is oeoxr'flDose l- B* -A;;,b)wnLcr _ s'T a' lo '.bose brr ac*,rg o-e orygen arci. e*2* sto,? s*gr sdp *mE

The strucrure of DNA can bc coEpared ro a ladder whichhrs been reisred i! a spiral. The ruDr! of lhc tadder arrromed by trvdro8en bolds lillkijrg rwo or8aoic bases wir.h AadeDrner alwavs li.nked wjrh T (rhymi_oe), snd C fc}losjlel

llwa"s lrnled wirh G (e1rB.'rj-De,. The sjdes of rhe .ladder. erctormed by altemadljs sugar aad phosphatc groups, I.E tlcactuar molecule Lhe DNA is dgtrdy coiled. TLe avclagclelgrh of DNA i-o a hulra.D chrc!]osoE. is abcur 1rr0 Eitloaoase !a!T wlllci rcpr6.Dl abour 14 EdltioD tuJls of rtrcsphr: ! lard our suzight jt would be l6s r.htE 5co Ioog.

STRUCTURE OF PORTION OF A DI1A OI.ECULE

DNA-THE DAUBLE HELIXNibosa b@ d@.kd b

CI.IABACTERISII{G DNA_A ER'EF HISTORY

,869. Friedrich lrieschner cre-icattr a.a.ysed rhe rLccrrsand o,scor'e.ed hu.lsin. wi.cn uas nol; o-or;in. h,gl Inphosphorus. miidly acid

1889 f,. Ahmann DJr ,€d rJcle.c ,crc, ano iderr,ted r.esugar 5nd the bases oF whrch it was comDrKe.t

,95O Erwlo Ct|argaff si-o4:d tna:,r an, salp€ o.D\a tteamoLr^l o'th,4-nre rs eoua,lo rrre arourr ol aoenire, ard rreamounr 0r closine eauals thar oi ou:nina

195:l JEmes_Watsoh and Frenci6 C.ick prcpose! rheoouore relx then approac-l sas treoreaca., baseo o^ heac-cJnJ a:ed evidelc€ o,r.ly oLrers, esoecrar/ lne i.ralo,flracl'or.o. purii,ed D\a oI Mei"..ce fft.ins a,ro FosatrnoFra*!- lvatso- C".t aro Vfi.r 1s $e.e ada,ded tne NooelPflze ror Physiology and Medrane in lqSA

P.23DNA neoNicationAs i1]e compl.lc geEeric messas: is .oDraiEcd withiD ilesequenc. of Lhe rucleoridB, rhere musr be a BechaEjsd forprecisdy duplicariag the molccuhr sfticrure. This is kno1{n

lf one ir.agines unz ppng tire DNAmoiecu e eaclr hali can a.l as atemplate lor a new .ha n ir lirts uayihe two cirains iorrned are dlplr:ates

as leplicatior: the ploduclio! of e second nole.ul€ of DN.Aexacrl! Iile rie tusr Erolecute. fte p2rc_ar motecu;e acrs a,

As a consequence ol repltcation, thecel can Lrnderso cell divisi.n. andeach of the reslliino cells has acoriplere rcpy o( rE geneirc m;rer:

I ftu u sd@tdt oi DNA ppa* k

,-C/ .(.\t1>\--) /\/b,l)'enild l+-n lt wo&,nia @/ -\.rb)M 7-nn tud \ /;;*\D\.4t"i*.,

=:M)M. ntntud \ /;;*\D\.4t"i*.,

=: /Vg ?/\

P,z+

.DEA & DtrA REpI,reA?roiE - gnEsTIoEE1, Giye the Jull Darne f,oi DgAl2"

: i"i.i"#lE::* of, iucreo-bidesr ihne the thlee parLE e,hiqh nah€,uF3, Describe the physical stluctule of DNA.4. t{hat uould be the length of DNA in a human if it. was leid outBtre ight?5. Dg:Fsribe the Froeesg ol DNA r.erdication.6. I.rr i.'hat yeer irere tu3t:9Ql Crick rnit witkills a{arded the NObeL prizefor physiology alld lled icine?

7

l GENEI]CS a 2qDNA strueture and replicatioer

By the 1920s, scieniisrs kaew rhat chromosomes consisted oimanv genes and tharchromosomes were made up {iom borh DNA (deoxyribonucleic acid) and prorein, bur noone knerv which was the hereditary material. Two researchers, james \Tarson and Fnncis Crick, suspecred rhar ir*u the DNA,

Bv 195J, Watson and Crick had worked our the smrcture ofDNA and rhar there are tbur niuogenous bases inils suucrure (adeDine, thymine, guanine and c.t-tosine). The criricalfinding thac unlocked rhe uoique prcpem,otDNA was rhar adenlne aiways paired rvirh thymine, while ct'cosine only paired *'irh gr.ranine. Walson and Crickused r.\is discovery to understand how DNA could divide and produce perfecr coples of iself and rhar thesequence of base pairs along a DNA molecule represented coded generic infomarion rhar could direci cell acdvin.

A. A nucteotjoe prospn*e q-o.p-O! \i!_oge'o_s oase| -

(g-an..e. qton-e, adeline. *Jrire)Ribdre !u6a.--\!

DNA structure

B. A functional length of DI{A: a qene -

--fi \fI ^ \,-'U * V\ryuAL :vents in the fi rst stage of mitosis 3nd rn€iots

1 Name the lour nitrogenous bases.How do .he niirogenous bases pair up in the DNA molecule? (See diagram B.)

(a) Relar: rhe DNA replicarion (diagrarn D) to events in rhe first srage ofmirosis and meiosis (diaEam C)(b) $lhat rvould happen in mirosis ii DNA replication did not occurl (Reyise miLosis.)(c) V1, at rvould happen in meiosis if DNA replrcaiion did not occurl (Revise meiosr

P.?6l GENETICSThe combined effect of genotype and

The development ofcells and ofan entire orgenism is gready influenced by geaesinherued from both parenrs and by the environment ofrhe developing organism.Ccnsider two genelicaliy identical planr: in differeni environmenis in rhe diagram below.

n Gen: Ol

IIu

/1

0-,a^) Zl rH bene( )

4, atr N lls"irc'eoo"- :: ' lr inorerpr:f,.d\ i Enwoih.i: t\ / Il\/I I c-bnsore

CLone B . en, o.renr! tl ii cto-e 6 celk

E1.'o_reneLfado'rneee.s on(oee1e [J o*.*-,r-*g.* ll

-"''-rH-- Eivi,onmenuiLtur iiusxil otsesr oe".. ll rean orsease geieII "\-''--*l-)-"UU

L.-,-.\*

PaEir ptait (iT) -* (t2

^.vYeCtonin! CetE froF

Pa.ent Plinl

a'.)

CtoneA in eryiroimeniX

Preventatjve medicine projeciEdu.a:iig the comn]unjty

to aYoid c€rlaineiviron eitatsliouti

Reptaciig deiective or

You are an Australian Coyemment Minisrer For Health. \bu have $l O0 million ro allocare ro one of thehealrh research projecis above. Which one wsuld re.eive y6ur fundinB? .lusrify vour choice.

environmefit on phenotype

H

List th.ee environmenLal factors rhar could cause a difference in phenoqpe (appearance) bet*'een rhe tuogene.ically identical planrs, clone A and cione B.

Study the diagram and s,rire a seremenr relaEing expression of phenotr''oe ro gene aclivarion b) envi.onmenr

There have been cases ofgeneticall] idendcal human tq,ins being separared ar birrh. Reunirin,s x adul*, theyofren do not closely resernble each other. Lisr three differeoces in their respecrive en!irooments Eha! malaccount for rhis.

Manyhuman diseases have a strong generic (farnily hisrory) factor and a stroog environmental facror.

List three environmenral factors which ma! aclivate:(a) inhericed cancer genes;(b) inherrred hean disease genes.

Heatth research impticattons

7P.z7

Lifestyie change ancj diabetes inAustralian Aborigines i.[Number 12. August ] 9841

Ausiralian Aborigines ale padiculariy wlnerable io diabeieswhen ihey make-ihe transiilon from i tradiiional io an urbanwav of li-fe. They share thls lrrlnerabiliiy with a number of otherpopulations r!hich have been subiected to rapid wbanisafion inihe twentieth century: numerous American Indian popLrJatiors,!he most well-knoi,'n erample being the Pima'ftidians inArizona, Nauruans and other Pacific Islanders, Indians and NewGuireans.

'In urbanised Aborighal communities as many as 25 people irevery 100 have ;liaber-es. Th.is js a much hlghei fi.eque;cy' thanamong Ausiraiiarc oI European descent (aboui S ii e"e'ry tOOpgople). Diabetes is associafed with a number of compLicitionsaffecting both Iarge and smali blood vesselsi Dabelics haveincreased risk of coronary heart djsease, slroke, lhrombosis,aiherosclerosG, blindness, renal disease, poor wound healirs,and gangrene. This extremely high prey-alence of diabetes fiAboriginal communities represents a serious health probiem.

People lrith diabetes- have much higher tlian normalconcenh'atiorLs of glucose in their blood due io a deficiency ofimutir. Insulin is the hormone rr'hich conlrols iranspori of firelssuch as glucose ftom the blood.stream inlo cells,lr'here they aieused as an energy sourcet Wiihoui a coniinuous suppiy ofenergy, the cells of the body will evenrually cease to funitioi. InT,?e 1 diabetes (ihe form of diabetes whiih is nrost common inyourg people) there is an absolute deficiency of insulin andpaiienLs aje dependent upon reg.tlJar injectioru of iruulin fortheir sulival. However, the mcre common fomr of diabeteswhich people get as rhey grow oider (Type 2 diabetes),is not dueio absoluie irsulir deficiencv but :ather to insulh resistance.This means lhat these people stili ploduce insulin but that thei-rboCy tissues are irsensitivi to it1 Iirs this type of diabetes whichis occurring in almosi epidemic proporlions in Aborigina!commurities when lhey change from a iraditional !o an urbanway of lifel This :ype of diabe:es arises out of the inie:action cf apre-exisiing genetic susceptibility with lifesiyle-associa{.edtrigger factors related to

P.28

famines. Ihere would.have been very stlong selection pressuresfor such a thriJty or efficient metaboGm_

However, with the change to an urban Iifestyle and itsasso€iaLed leduction in energy eipenditure (physiial activifv)and increase in energy intake'iieadity a"altaUtj toloj zuppfy ri?(il-energy derue foods such as sugjr, fat and alcoholi, such anefficient metabolism promotes obiity and eveniuallv diabetes.In this way it is p-ossible ro iin( successful slrvival ashunter_gaihercls with sus.epiibility to obesity and diabetes intne 1uban setirrrE.

..]:,:,:}of :r _: group of,diaberics from ihe Mowan/umaboriginal communilyjn the {ar north_wesi of WesiernAustralia, Dr Kerin C).Dea and colleagues shoilea thai arelatively short r"hrm.to traditional t u-i'f.r_gu il.,.i"i tU".t"t.(seven vieek) resulted ina dramatic improveir"nt jo "ii;'ih;metabolic abnoraatities of diabetes. Th" io"fts oi t'f.ri"'sfray

"re3 "q$nt i.l.iushation. of .the relationship Uet*een'iUestyij anahealth and show that diabetes is "ot

dnlv ieu"iriU-tin tf..,esepeople, but poteniially preventable. The gU'o.igir,e, inihir.h:a"were,very.impressed with the possibility of un"derstandlne wilirney nad drabetes and hoiy they could treat it themselvesl Tlr-G;.ydl.tLiChUgnted rhe imporrance of three aspects oiiiiaitio*truestyle whrci musi be incorporaled into ani future preveniivel-11]ll. .pl"C'?l*,,tf. rhey .are ro be s ,ccessfiil: regu)a'r physicalacrrvrry, Iow Iat diets, weight conkol. The same pr-inciplis ior:lda.lso be appued to the treahment ard prevention of rlijs ,wr" ^rciiabetes in Australians of European d&ent.

Q$EEEIONA.1" Briefly describe the tqro types of diabetes .2. E{hich t.ype is causing llloEt eoncern i:r the Aboriginal population?3. Compare the pereenLage of AusLra-[ j.an Aborjgines rttl., ai"Uet"= tot.hose of Australians of European descent,4. ldhat is the name of the hormone that is deficlent 1n diabetes? t{hati.a iLs funct ion?5. EoH can dlabetes be detected?6, i{hat is t'be cause of thls diBease: genes. environm€nt or both?Exp.lain.

1" goir can an ancient survr"val advantage (the abilj.ty to store bodyfat effectively), be a disadvantage in todal.'s urLan environm€nt?6; tthat happened when a gioup of diabetic aboriginale returned Lo atraditlonal hunte-r-gaaherer lifestyle?

1. Hhat advice should be given t.o aI.I Australians conceining thePreventlon and treaLmenL of type II drabeies?

P,23Gerles, ChroEssomeE and XaryctyEleE

:I:?:r.Mg"dgJ, ttA22-A41, an,Auguscihi.an.Monk, waa the lrist person .LoeEucly lnheritance in a Eci.*," i"" '"i-i""-";;.;1.: ;;':":::i;,":l.rl:".:l::lil;i:"ry::i:r::!irli:.characteriEtics were inhe-i.red. i "a.p."a. nt iy-J; -i;::;...

pEckers ofinformation he cal Jed 'fact-ors'Mende 1_Fubl i Eheil ar] account-of.his woik in a lj.ttle knoren jour-!}ai injlj;;.rn" doeu,nenr attracrec r,ilii" "ll"ni,L';;;ii I:;" yeare a+er hi.s

Il.1:91' sutton'-an American, noticed the Eimirarity betl.ee!) theDenavrour of Mehdel ,s facrors and the cay ;;;;;;;;;:.;"re seen !obenave du!ing rneiosis, Ite cohcluded tr,"r-v--,r--i ij-fII.l::':f:'jf;:,::*"*i::"il"i:':I:"*.:;;"il:1";i.:.':::;::.":3re ca!riedrhe factors ;."'"".1 "} iJi';";:::t"""'"

came in pairB Iike E'he t"ii".".

Il:,"1r, time thet ke are able to see chrohoBomes clearly is when lhecell is about ready to divide, The of, roro" o...".-i iiil."a"". fl...ahorLened and rhickened ".a 6y" "i=ifj.-;;-;;; ;;.;;jj;id arm..

Each specj"es has its own uniquesel of chromosoroeE. This sel.ra ealled its karyotype. Tnealagram ahorca what vou are]ikely to see on a etiae ot aiujnan cel.[ getting ready toIt iE the eell of a human male.

{z y- # €7}6 q'

te=#ig,-##:l-?>#k" "1V Hi$-# *_

,f*e4

#

a!'e matehed end pairedTo aee a ke ryotype mole c.leariy the chromosomes

l,al0

16

21 2?

ExF!tgtr$ ffH $fi

eUd!ft

s

tvilft

6

;"fld!13

19

)lHai le

7

(i r'l

l1

irl2A

aunnI

ilh

\!vnn

sl,

5

nri1211

&fi 6E17 18

tEr

erF+J.

tsFlrxx

P.30

Hu$ans have 46 chromosornes, 22-Fairs of these are carred autosomes andale the same in males and femal.ls. rr,. f."J'i.i.""il'iatrea ele se.xchronosomes. A hale has one x anal "a. v -"iioii"-o.l'ili

r. t.r"i." t"o.trdo x chromoEomes. ?he mare y chromosome -ii -;;;;-;Jii"" rhan rhe x andso canoot carry as ,nany qenes. This is th" ;;;";;-;;y sohe geheticcond:trcns, eg. red-green coiour b.lindneg.,-ri-i".. ior*on ,r, ,aI.",Gerea

l{e have only 46 chro:nosonres lgq *e heve hany more recogniBablecha'actertsrics, This m€anE EI.t our "hr;;;1";";-;;;"each, piobably arouna roo, ooo. i, "lt. d;;;;-;'"-iti"ii..3il5,"l::I.r:;:=nearl y a.lreays inherited logether.

ExaDl,les{1)

Ear sizet]

il-U

:.+

.rc ;" ".t ,f"d -r' -t< ^l.a\c- -+' ^c.s' .^€

rolllongue fl+ Hair colour€ Abserce of indsor teeth

Hair whorl

C.oss-eyednessEye colour

A iinkage of genes o'r rhe hurdan X chromosorn. (ndr ro scale),

llai! colour iE controlled by a nulrber of interactj.ng gener that produeell?*_"!!: metanin beins.one, rhe hole hetanin p;;;;;ir; senes we have,lne oarker our ha.i.r. ThlB type of inheritence rs callad polygenic as Lx_rs cont.rolled by hore than on" g"n..Sohe genes eye described as dominant while ot.hers are recesEive. someexampleB, for humanE, are Bhoi,rn beloi{.

Dart h3ir Blond hairCurly hair Smishr haitEarly bajdncss (malcs) lio laldncssBro*n .y.s Bllc

vP.31

Any change in a gene, chromosome. or the nurnbe. of chromoeomes is calleda hutatior?. Hutations that occur',in nortlat body ""rf" "i"-oo; inheriteal?hoB€ tshar occur in the sex cettE m"y le i"ir"iiteJ-iia-i!,,jir ;." .nunexpected change ia the offBpring. !.rost hutationB ".".. pr"lf"r",genetic diseaBes being an exahple.ExaEpleB of Genetic DiseaEes include, colour blindness. rnus.u.tar:I::I:flI: haemophilia, -pKU, rurner' E syndrolDe, r;",.;"'sv,i,"*",::.rr"::Ti. etc- sorDe of theBe are caused by sehe murari;ns ee.naemophltta, otherE are caused by"tbe gain or loEs of a chiomouo." eg.Down's syDctrohe, utations ","."ity ""6", *nit" tr,"-ir,i"#iir"" "."beins copied, xhat is durjns nixosjs or."i"";;.-"-can ]'ou aee the abnormatiry ir. the karyorypeE below?

fle fffl fiI123

)f trfi45

Itx xx11 12

aj$grrE

!

8

AN15

Y'K HK tfi123

6tfl fift,t5

iJ !,/inxx?2

d,t rT fil5X,t xr ,{{ )rx [r5 7 8 s io

13# E&61il &t\12

HX dr #|{ ftfi dfi fffi6 7 8 I 10 11

t1,]12fifi fiR dfi

13 11 15N'{ l{H d(16 17 13

r9

xx20

; i ir21 22

!u11[\ x

dn13

19

l, ,1 n615

16 fiE XN16 17 18

22

aa21

fi

KaryotFe of a persos with Ktin.fclrcr's syldrome. fraryot1pe ofa person wirh ?uiEe.,s s}!d.ome.

XH6

nn13

'E

f,a7

An1,1

20

R*I

HH H6 H610 11 t

xx xx dd'16 1t l8EB I

21

Raryorype of a pe:sor with Do$E,s 6ynd.oroe,

p.32I

TeaXing far ceneti.c Dibeases

lloaleln Lechnotogy haE develol,ed Lechniques to delect sorqe of the geneticdieeaees in the developing foetus" ?here are tldo wide.Iy used techDiques,

a) Chorion Biops1lThi6 involves taking ce.!!a from a part of the Bae called Lhe

chorioh. fhese ce1.ls are identlcal to the foetue; they are cultured,l

\

P.33&'l uta tia *s- ge* efa rrt aWMutations are changes in genetic material. Sometimes largepads ofa chromosoEe are affecred, sometimes the change iswithid one gene.

Nearlt all hutations are Larmful. This is hardly surprising, asthe existing geir€s ofan organism already work well iogether.Missing genes, exha genes and ehaaged genes are almost boundto upset thesyst€m.It can mean death. Not all Dutatioas causeehanges as large as the onesin the example.

A few mutations are useful r,o the organisms in which iheyhappen. Our distanr ancestors did no'r look like us.jodglng bytheirfossilized bones. As useful rdutaiions h.pp"n"d, org"ais-.gradually became more like those living ioday.

Misrakesin genes can happen anyway, but more rnu!aLionshappen wheD anorgaaism is exposed io ra d iatioh or chemicalslike muslard gas and LSD. Mu!ation irr body celjs may resulE jn acancer. Muiations'in cells which become gametes mean that thehistakes can be passed to oflspring -genetic diseases mayresult.This is vcry worrying as humans are using roo."

"o,rr""s of

ladiatioh (Duclear. bombs, auclear po*,er slations) and more newchemicals which carget into ou. food or the air we breathe.It isfor this reason that pregrrant women should be X-rayed as rareil,as possible

GeEetic diseasesAn example - sickle-cell anaemia-A personwith sickle-cell anaemia has red blood cei16 whichbecome clrawl out and cannot cerrl- oxJ'gen properly ror.rnd thebody. lt rs caused by a mistake irr a gene invol.ed in makinghaemoglobiu - usuallycalled IIbs. The normal gene is FIbF_

These f.uir flies have hurations whichwolld meen lheir dealh i. the wild.

si.kled red blood .elt

Here is a fatlily in which theparents are both heterozygousfor thiE gene. Dominance isincomplete.

Ttlere are maDy gelleticdiseases, such as cystic frbrosis,phenylketatruria andHuntiEgtor)'s chorea. Most areunpleasant, and iftheir namesare unfamiiiarit is becausemostly they are rare.

One special gtoup olmutations are the sex-linked ones wherechanges happeD in the X chromosone. Tbe resuli is interesting- Ifa man has the mutated gene as part ofthe X chromosome the -effects will show. as lhelf chromosome hasn t got a gene to make!p for the deficiency. Ifa *.oman has one X chromosime with amutation.andonenormal one she appeerstobehormal-bursheis a carrier. A wornan only shows the effecrs ifshe has rwodamaged X chromosomes.

I

chromosorne missing .

Huhan chromosomewilh a vsibe muratio.

P HbS HbN I

._E trQ sos r.ro,

EE-- tr {} Er-r :J-,",,A"\-\^ 'E )l - orood

o"_",."(?_(o) (Hb) (Hb\) E

, Efr-*h.>l*})*H'ff.|i, fr!."# lp*$" ii,";fihealthy, no sicale cells L- 51;91 rl, ....-;. I ral! siclie ceJs, very

an.enic, probabl! d es young

v

P-3+

Colour.blindness is a fairlycommon example. Sexchrorrrosomes have genes forcharacteristics besides sex. Theabiiity to see colour is one ofthera. llere is a fami)y in whichthe moiher has a hjdden Renelor eolour-blindness. Her sightis normal.

The clues to sex linkage are:(a) It is dearly al!.rays males who suffer-{b '1hey oniy sufler from sex-l:nked diseases because their

mothers are carders. FroEt their fatherc ihe)'inherii a Ychromosoile which isn't allecteC.

(c) You can only teii rhat a wohaD is a carrier ifshe has sons*'ho are affected-

A famous sexliEked disease ishaemophilia. Haemophiliacs -'bleeders'- have blood whichCoesn't clot propelly. Theyoften die young. ic i: a raredisease, but Queen Victoriawas a carrier for it, perhaps asthe resull ofa mutation in agene in one ofthe Xchrornosomes she inheriaedf.om her parents. Sh€ passed iion to he; children, and rhe genespread through severalEuropean royai houses. It nodoubl affected history.

gSEaTIOICE "

.1. !,{hat is a mu:ation?2. lghy is it mos: llke]y that a mutation wilt be hahiut?3. Why is it sometimes staLed that ,'mutations are the tari, material olevo.l uti.on "?4. liame tero chen::cals and one form of energy lhat cause mutations.5. Name tour genetic diBeases.6. tihen ie a Hor0an a ,car!ier, of a sex,li.nked disease?7" Name tr*o sex linked diseases, tlho suffers xrostly from these

8. Hhat effecls a.re there, of having the sex linked diEF^rphaenrophi t ia ?

B.c o-a

'ad -e--odbo: St -=..t.

irl no.-ca ier giriboih have ncrma colour vision

. Ldf .j, .t, -,-.rL