KEY CONCEPTS

1. Definition

2. Revision from gr 11:

• Homologous chromosomes

• Paternal/maternal chromosomes

• Diploid/haploid

• Somatic cell/body cell

GeneticsGenetics

• Genetics is the study of Genetics is the study of heredityheredity• It deals with the It deals with the similarities and differences similarities and differences

between between parents and their offspring parents and their offspring • In Genetics we look at In Genetics we look at how characteristics how characteristics

are passed from one generation to the are passed from one generation to the next.next.

• GenesGenes carry the hereditary information on carry the hereditary information on chromosomes.chromosomes.

1

4

WHAT IS GENETICS

JESSICA ALBA GETS MARRIED

Chromosomes, DNA & Chromosomes, DNA & GenesGenes

KEY CONCEPTS1. Locus(i)

2. Alleles

3. Genome

4. Dominance & Recessiveness

5. Karyotype

6. Genotype

7. Phenotype

8. Homozygous

9. Heterozygous

GeneticsGenetics• Let us look at the human characteristic

of having a free or attached earlobe

YES This ear is attached

• Click on the attached lobe

This lobe is FREE

2

GeneticsGenetics

Attached lobeAttached lobe Free lobeFree lobe

3

Attached lobeAttached lobe

•Genes occur in pairs Genes occur in pairs

•If we represent the gene for If we represent the gene for attached ear lobe as little “e”attached ear lobe as little “e”•Then this persons gene pair Then this persons gene pair will be “ee”will be “ee”

ee ee

4

Genetic TermsGenetic Terms

ee ee

GENOTYPEGENOTYPEThe genes that The genes that

code for a code for a characteristic e.g. characteristic e.g.

eeee

PHENOTYPEPHENOTYPEThe characteristic The characteristic expressed by the expressed by the

gene e.g. attached gene e.g. attached ear lobeear lobe

ALLELEALLELEgenes are partnersgenes are partners of each other:“e” of each other:“e” is an allele of “e”is an allele of “e”

5

Looking at the genes on ChromosomesLooking at the genes on Chromosomes

E Ee e

Attached lobeAttached lobe Free lobeFree lobe

The gene for free The gene for free lobe is “E”lobe is “E”

The genes occur The genes occur in pairs on in pairs on

chromosomeschromosomes

6

E Ee e

Attached lobeAttached lobe Free lobeFree lobe

The genes occur at special positions on The genes occur at special positions on chromosomes called loci.chromosomes called loci.

One version of the gene is inherited from One version of the gene is inherited from the father , the other from the motherthe father , the other from the mother

If the two genes are the same e.g. ee or If the two genes are the same e.g. ee or EE they are EE they are homozygoushomozygous..

7

E e

There can be a mixture of attached and There can be a mixture of attached and free ear lobe genes (Ee)- free ear lobe genes (Ee)- heterozygousheterozygous..

One gene, in this case (E) is One gene, in this case (E) is dominantdominant over unattached lobe (e) which is called over unattached lobe (e) which is called recessiverecessive

In this case the E gene completely In this case the E gene completely supresses the expression of e gene so supresses the expression of e gene so this persons will have this persons will have free ear lobesfree ear lobes

8

Summary Three possible genotypes…Summary Three possible genotypes…

E Ee e

Attached lobeAttached lobe Free lobeFree lobe

Homozygous Homozygous dominantdominant

Homozygous Homozygous recessive recessive

PHENOTYPEPHENOTYPE

GENOTYPEGENOTYPE

E e

Heterozygous Heterozygous dominantdominant

9

Alleles

Alleles

Bb

1. The two genes on homologous chromosomes that code for the same characteristic are found on identical locations on the pair of chromosomes, called loci (singular: locus) pg 5

2. Alleles are alternate forms of a gene located on the same locus of homologous chromosomes.

3. It seems that sometimes, one gene dominates the other of the pair. We say that the one gene is dominant, while the one that is dominated, is called the recessive gene (pg5).

4. A genotype Bb is called HETEROZYGOUS (or hybrid). Here the paired genes (ALLELS) for a particular trait (characteristic) are different (pg 6).

5. A genotype BB or bb is HOMOZYGOUS. Here the paired genes (ALLELES) for a particular trait (characteristic) ore identical (7)`

BL**DY IMPORTANT DEFINITIONS

1. The characteristics that we can see in an individual, for example, brown eyes, is known as the PHENOTYPE (pg 6).

2. The letters Bb indicate to us the GENOTYPE for eye colour, that is, its genetic makeup (pg 6).

BL**DY IMPORTANT DEFINITIONS

Looking at our example of earlobes.Looking at our example of earlobes.

What possible offspring can be produced if:What possible offspring can be produced if:

The male parent hasThe male parent has

ATTACHED lobesATTACHED lobes

(ee)(ee)

The female parent hasThe female parent has

FREE lobesFREE lobes

(EE)(EE)

1

Firstly we need to look Firstly we need to look at the formation of at the formation of sperm cells (male sperm cells (male

gametes in the testes) gametes in the testes) to see the different to see the different

types of sperm cell that types of sperm cell that can be produced from can be produced from

this ee parent.this ee parent.

2

e e e e

Looking at one cell in the testes dividing by meiosisLooking at one cell in the testes dividing by meiosis

Cell with double Cell with double stranded chromosome stranded chromosome

pair with e-genespair with e-genes

3

e e e e

Cell divides by meiosisCell divides by meiosis

4

e e e e

End of the first End of the first MEIOTIC division MEIOTIC division

Chromosomes have Chromosomes have separatedseparated

5

e ee e

Second MEIOTIC Second MEIOTIC division division

6

e e e e

End of the second MEIOTIC End of the second MEIOTIC division – FOUR sperm cells are division – FOUR sperm cells are produced, each with a e-geneproduced, each with a e-gene

7

e e ee e

E

In this case there is only one type of sperm In this case there is only one type of sperm cell that can be produced – all have e-genecell that can be produced – all have e-gene

In the same way, the In the same way, the female will produce egg female will produce egg cells in the ovary. cells in the ovary.

As she is EE she will only As she is EE she will only produce one type of egg produce one type of egg cell with the E-genecell with the E-gene

EEEE eeee

8

eE

E e

All the offspring from these parents will All the offspring from these parents will have a Ee genotype – They will ALL have have a Ee genotype – They will ALL have

Free ear lobesFree ear lobes

The sperm The sperm and egg cells and egg cells fuse to form a fuse to form a

new childnew child

EEEE eeee

9

Punnett Square

GAMETES

E E

e

e

Ee Ee

Ee Ee

Now what if both parents are heterozygous Now what if both parents are heterozygous (Ee) What are the possible offspring?(Ee) What are the possible offspring?

The male parent hasThe male parent has

ATTACHED lobesATTACHED lobes

(Ee)(Ee)

The female parent hasThe female parent has

ATTACHED lobesATTACHED lobes

(Ee)(Ee)

1

E E e e

Cell with double Cell with double stranded chromosome stranded chromosome pair with E and e genespair with E and e genes

Looking at one cell in the testes dividing by meiosisLooking at one cell in the testes dividing by meiosis2

E E e e

Cell divides by meiosisCell divides by meiosis

3

E E e e

End of the first End of the first MEIOTIC division MEIOTIC division

Chromosomes have Chromosomes have separatedseparated

4

E E e e

Second MEIOTIC Second MEIOTIC division division

5

E E e e

End of the second MEIOTIC division: End of the second MEIOTIC division: FOUR sperm cells are produced, TWO FOUR sperm cells are produced, TWO with an E-gene and TWO with e-genewith an E-gene and TWO with e-gene

6

E e eE

Two types of sperm cells can be produced- Two types of sperm cells can be produced- ONE with a e-gene and one with a E-geneONE with a e-gene and one with a E-gene

7

E E e e

Looking at one cell in the ovary dividing by meiosisLooking at one cell in the ovary dividing by meiosis8

E E e e

9

E E e e

10

E E e e

11

E E e e

12

E e eE

Two types of egg cells can be produced- Two types of egg cells can be produced- ONE with a e-gene and one with a E-geneONE with a e-gene and one with a E-gene

13

E

e

14

E e

E

e

What possible offspring can be What possible offspring can be produced when these sperm and produced when these sperm and

egg cells fuse?egg cells fuse?

15

E e

E

e

E

E e

e

E EE eE

If a e-sperm If a e-sperm fuses with a fuses with a E-egg, the E-egg, the

child will be child will be Ee -Free LobeEe -Free Lobe

If a E-sperm If a E-sperm fuses with a fuses with a E-egg, the E-egg, the

child will be child will be EE -Free LobeEE -Free Lobe

16

E e

E

e

E

E e

e

E EE eE

e

e

eee

E

eE

In the same In the same way …way …

17

ee

eeEE

EE EEEE EeEe

EeEe eeee

male gametesmale gametes

fem

ale

gam

ete

sfe

male

gam

ete

s

To simplify this we use a Punnett square To simplify this we use a Punnett square to show possible offspringto show possible offspring

3 out of 4 3 out of 4 free lobesfree lobes

1 out of 4 1 out of 4 attached attached lobelobe

Possible offspringPossible offspring

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If for example marries

P1 (first parental generation) Bb x bb (Brown-eyed male) (blue-eyed female) Meiosis Meiosis B b b b

Male gametes (sperm) Female gametes (egg cells)

Female gametes

♀

We use what is called a PUNNET SQUARE Male gametes ♂ (symbol for male)

GAMETES B b

b Bb bb

b Bb bb

Punnett Square

GAMETES

B b

b

b

Bb bb

Bb bb

• PhenotypePhenotype: : Half are Brown-eyed, Half are Brown-eyed, half are blue-eyed (1:1)half are blue-eyed (1:1)

• GenotypeGenotype: : halfhalf are are heterozygous heterozygous brown (Bb)brown (Bb) and and halfhalf are are homozygous blue (bb): 1Bb:1Bb homozygous blue (bb): 1Bb:1Bb

We use what is called a PUNNET SQUARE Male gametes ♂ (symbol for male)

GAMETES B b

b Bb bb

b Bb bb

Why can two brown-eyed parents have a blue-eyed child?

P1 Bb x Bb P1 Meiosis

B or b B or b ratio of gametes Fertilisation F1

1 homozygous brown (BB) 2 heterozygous brown (Bb) 1 homozygous blue (bb)

(F1 = first filial generation, in other words, the possible types of eye-colour of children the parents may have)

The PHENOTYPIC RATIO: 3 brown-eyed child:1 blue-eyed child

The GENOTYPIC RATIO:

1 homozygous brown (BB): 2 heterozygous brown (Bb): 1 homozygous blue (bb)

1BB:2Bb:1bb or 25%BB:50%Bb:25%bb

GAMETES B b

B

b

BB

Bb

Bb

bb

e.g., Tall Plants x Short Plants

Let T = gene for tallness

Let t = gene for shortness (note: you must use the same letter for a characteristic)

P1 TT x tt P1 (crossed 2 homozygous plants)

T T t t (Gametes)

Fertilisation

F1 (Punnet square)

All the offspring of F1 will be Tt (heterozygous tall)

Thus, Mendel said that when two characteristics meet in an individual, one dominates over the other, called the recessive

(LAW OF DOMINANCE AND RECESSIVENESS).

GAMETES t t

T

T

Tt

Tt

Tt

Tt

Mendel took the offspring from F1 (Tt) and crossed them

P2 Tt x Tt P2 (2nd Parental generation)

Meiosis

T t T t gametes

Fertilisation F2

1 homozygous tall (TT)

2 heterozygous Tall (Tt)

1 homozygous short (tt)

GAMETES T t

T

t

TT

Tt

Tt

tt

Mendel’s law: Mendel’s law: INDEPENDENT ASSORTMENTINDEPENDENT ASSORTMENT

• Independent assortment occurs during Independent assortment occurs during meiosis I, specifically , specifically metaphase I of of meiosismeiosis, to produce a gamete with a , to produce a gamete with a mixture of the organism's maternal mixture of the organism's maternal and paternal chromosomes. Along with and paternal chromosomes. Along with chromosomal crossover, , this process this process aids in increasing genetic diversity by aids in increasing genetic diversity by producing novel genetic combinations.producing novel genetic combinations.

MEIOSIS – Prophase IMEIOSIS – Prophase I

Crossing OverCrossing Over

As homologous

pairs line up, crossing over occurs

This happens when partner chromosome

s swop pieces of chromatid

Chromatids from partner chromosomes cross over

Pieces of chromosome are swopped

This mixes This mixes genetic genetic material material

and bringsand bringsvarietyvariety

3

Crossing Over brings VariationCrossing Over brings Variation

Four different Four different types of types of

chromatidschromatids

TwoTwo

Instead ofInstead of

4

MEIOSIS – Metaphase IMEIOSIS – Metaphase I --

Homologous Homologous chromosomechromosome

s line up s line up IN PAIRSIN PAIRS

at the at the equatorequator

The The chromosome chromosome pairs can line pairs can line up in differentup in different

combinations – combinations – this this

brings brings variety variety

5

How many possible combinations are How many possible combinations are there ?there ?

With 2 With 2 chromosome chromosome

pairs (2) there pairs (2) there are 4 possible are 4 possible combinationscombinations

2222 = 4 = 4

This is called This is called independent independent assortmentassortment

6

How many possible combinations are How many possible combinations are there ?there ?

What possible What possible combinations are combinations are

there with 23 there with 23 pairs?pairs?

222323 = ? = ?8 388 6088 388 608

Remember this is Remember this is without crossing over without crossing over and just in a sperm or and just in a sperm or

egg cell!!egg cell!!

7

• In In independent assortmentindependent assortment the homologous the homologous chromosomes separate randomly during chromosomes separate randomly during Anaphase Anaphase I of Meiosis I. I of Meiosis I. Chromosomes that end up in a Chromosomes that end up in a newly-formed gamete are randomly sorted from all newly-formed gamete are randomly sorted from all possible combinations of maternal and paternal possible combinations of maternal and paternal chromosomes. chromosomes.

• Because gametes end up with a random mix instead Because gametes end up with a random mix instead of a pre-defined "set" from either parent, gametes of a pre-defined "set" from either parent, gametes are therefore considered assorted independently. As are therefore considered assorted independently. As such, the gamete can end up with any combination such, the gamete can end up with any combination of paternal or maternal chromosomes.of paternal or maternal chromosomes.

Mendel’s law: Mendel’s law: INDEPENDENT ASSORTMENTINDEPENDENT ASSORTMENT

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

• In Gauteng, we often see cosmos In Gauteng, we often see cosmos flowers on the side of roads at flowers on the side of roads at the end of summer. We see red, the end of summer. We see red, white and purple flowers. Why?white and purple flowers. Why?

Incomplete DominanceIncomplete Dominance

Incomplete Dominance occurs when the Incomplete Dominance occurs when the offspring show a combination of recessive offspring show a combination of recessive and dominant characteristicsand dominant characteristics

PurePure Red flowersRed flowers crossed withcrossed with White White flowersflowers produce allproduce all pink flowerspink flowers in the Fin the F1 1

generation.generation.

1

INCOMPLETE DOMINANCE

• Let R = gene for red snapdragons

• Let W = gene for white snapdragons

GENOTYPE PHENOTYPE

CRCR Red Flowers

CRCW Pink flowers

CWCW White flowers

P1 CRCR x CWCW P1 (crossed 2 homozygous plants)

CR CR CW CW (Gametes)

Fetilisation F1 (Punnet square)

GAMETES CR CR

CW

CW

INCOMPLETE INCOMPLETE DOMINANCEDOMINANCE

CRCW

CRCW

CRCW

CRCW

• Phenotype: 1 red: Phenotype: 1 red: 2 pink2 pink: 1 white: 1 white

• The genes are unaltered by this The genes are unaltered by this phenomenonphenomenon

INCOMPLETE INCOMPLETE DOMINANCEDOMINANCE

If CRCW is crossed with CRCW the result will be

F2

GAMETES CR CW

CR

CW

CRCR

CRCW

CRCW

CWCW

CO-DOMINANCECO-DOMINANCE

PARENTS Phenotype: Red x White Key: R – Red coat W – White coat

Genotype: IRIR x IWIW

MEIOSIS

GAMETES IR IR IW IW

FERTIISATION

GAMETES IR IR

IW

IW

IRIW

IRIW

IRIW

IRIW

Looking at co-dominance when pure bred Looking at co-dominance when pure bred (homozygous) red and white cattle are (homozygous) red and white cattle are

bred.bred.

PP11

FF11

White cowWhite cowRed BullRed BullIIRRIIRR IIWWIIWW

CCRR CCWW

All IAll IRRIIWW (Roan) Offspring are produced (Roan) Offspring are produced

GenotypeGenotype

GametesGametes

2

GAMETES R R

W

W

RW

RW

RW

RW

GENOTYPE: ALL HETEROZYGOUS RWPHENOTYPE: ALL ROAN

• F2Genotype: 1 IF2Genotype: 1 IRR I IRR: 2 I: 2 IRR I IWW: 1 I: 1 IWW I IWW

• F2 Phenotype:F2 Phenotype: 1 RED: 2 ROAN: 1 1 RED: 2 ROAN: 1 WHITEWHITE

CO-DOMINANCECO-DOMINANCE

P2 (F1) Phenotype: Roan Roan

IR IW x IR IW

MEIOSIS

GAMETES IR IW IR IW

FERTIISATION

GAMETES IR IW

IR IR IR IR IW

IW IR IW IW IW

GAMETES R W

R

W

RR

RW

RW

WW

Genotype: 1 RR: 2 RW: 1 WWPhenotype: 1 RED: 2 ROAN: 1 WHITE

WHAT ARE THE CHANCES OF HAVING A BOY OR GIRL ON THIS BASIS ALONE? _______%

MALE FEMALE

PARENT XY BODY CELL XX

MEIOSIS

GAMETES X Y X X

FERTILISATION

ZYGOTE

[OFFSPRING/PROGENY] XX XX XY XY

50%

X

X

X

Y

SEX-LINKED INHERITANCE

Some Characteristics, like the gene for colour vision are found attached to the X chromosome. This means that the gene for that characteristic is linked to the sex of the individual.

Do you notice that the male’s X chromosome does not have corresponding loci on the Y chromosome because it is shorter. Thus even a recessive gene on the X chr. will be expressed.

X

X

X

Y

BB bb bb

In humans, the gene for colour vision is sex-linked. The gene is linked to the X chromosome. The gene for normal colour vision (B) is dominant over the gene for colour blindness (b).

If the female parent (XX) has normal vision (Bb) and the male (XY) is colour blind (b – only on the X)…

XBXb XbY

YXX X

If the female parent (XX) has normal If the female parent (XX) has normal vision (BB) and the male (XY) is colour vision (BB) and the male (XY) is colour blind (b –only on the X)…blind (b –only on the X)…

How do we link the colour blind genes to How do we link the colour blind genes to the sex chromosomes ?the sex chromosomes ?

SEX-LINKED INHERITANCESEX-LINKED INHERITANCE8

YXX X

Normal FemaleNormal Female

BB on the X BB on the X chromosomeschromosomes

SEX-LINKED INHERITANCESEX-LINKED INHERITANCE

BB BB bb

Colour Blind maleColour Blind male

b on the X b on the X chromosome onlychromosome only

9

Y

XXBB

XXBB

XXbb

YY

Normal Normal Female Female

Normal female Normal female possible egg cellspossible egg cells

X

BB

XX

bb

Colour Colour Blind Blind Male Male

Normal Female x Colour Blind MaleNormal Female x Colour Blind Male

Colour blind male Colour blind male possible sperm cellspossible sperm cells

X

BB

10

Y

YX X

Y

X

Normal Female Normal Female but carries the (b) but carries the (b) colour blind genecolour blind gene

Normal MaleNormal Male

XX

BB

X

BB

XX

bb

bb BBBB

X

BB

XX

bb

XXBB

XXBB

Normal Normal Female Female

XXbb

YY

Colour Colour Blind Blind Male Male

Normal Female x Colour Blind MaleNormal Female x Colour Blind Male

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XXbb

YYXXBB

XXBB XXBBXXBB XXBBYY

XXBBXXbb XXbbYY

Normal male gametesNormal male gametes

Carr

ier

fem

ale

C

arr

ier

fem

ale

g

am

ete

sg

am

ete

s

What are the possible offspring that would What are the possible offspring that would result from a carrier female and normal male ?result from a carrier female and normal male ?

Possible GENOTYPEPossible GENOTYPE

11

33

22

44

1 1 Normal Normal femalefemale

2 2 Normal Normal malemale

3 3 Carrier Carrier femalefemale

4 4 Colour Colour blind maleblind male

PHENOTYPEPHENOTYPE

12

What are the possible offspring that would result from a carrier female and normal male?

P1 XBXb x XBY

meiosis

gametes XB Xb XB Y

FERTIISATION

GAMETES XB Y

XB

Xb

F2: Genotype: _____________________________________________

Phenotype: _____________________________________________

_____________________________________________

XBXB

XBY

XBXb

XbY

1 XBXB: 1XBXb: 1 XBY: 1 XbY1 FEMALE NORMAL: 1 FEMALE NORMAL CARRIER: 1 MALE NORMAL: 1 MALE COLOURBLIND

BLOOD GROUPS

• CO-DOMINANCE

• MULTIPLE ALLELES

ABO blood groups in humans Important because ABO blood groups affect blood transfusions

o Genes cause expression of sugar groups on surface of red blood cell membrane; these carbohydrates act as antigens in immune reactions

o 3 alleles: A, B, O o A & B dominant over O o A & B co-dominant to each other o Type O produces no sugar antigens o 6 genotypes and 4 phenotypes

 Phenotype  Genotypes

 A  AA (IAIA) or AO (IAi)

 B  BB (IBIB) or BO (Ibi)

 AB  AB (IAIB)

 O  OO (ii)

Blood GroupsBlood Groups

e.g., Cross a homozygous group A man with a heterozygous group B women to find the

F1

PHENOTYPE A (IA IA) x B (IBi)

GENOTYPE

GAMETES

F1

GENOTYPE: _______________________________________________________

PHENOTYPE:_______________________________________________________

GAMETES

IAIB

IA

IB

IA

i

IAIB

IA i IA i

50% = IA i 50% = IAIB

50% = A 50% = AB

Blood GroupsBlood GroupsCross a homozygous group A man with a heterozygous group B women to find the

F1

PHENOTYPE A x B

GENOTYPE

GAMETES

GAMETES

F1 GENOTYPE:

PHENOTYPE:

AA BO

A A

B

O

AB AB

AO AO

2 AB:2AO

50% GROUP A: 50% AB

BLOOD GROUPSBLOOD GROUPS

BLOOD TYPE OFRECIPIENT ANTIBODIE

SDONOR

A B A, OB A B, O

AB NONE A, B, AB, OO A & B O

BLOOD TRANSFUSIONBefore a person (recipient) receives blood, the blood of the donor has to be first tested to ensure that it is not infected and is of the right type.The table below shows the safe donor for recipients of the various blood types:

BLOOD TYPE OF PARENTS

BLOOD TYPE OF CHILDREN

AB x AB A, AB, B AB x A A, AB, B AB x B A, AB, B AB x O A, B A x A A, O A x B AB, A, B, O A x O A, O B x B B, O B x O B, O O x O O

Blood GroupsBlood Groups

AB X AB = A, AB, B

GAMETESGAMETES A (IA (IAA)) B (IB (IBB))A (IA (IAA)) AA AA

(I(IAAIIAA))AB AB (I(IAAIIBB))

B (IB (IBB)) AB AB (I(IAAIIBB)) BB BB (I(IBBIIBB))

BLOOD TRANSFUSIONBLOOD TRANSFUSION

recipient donor

A A or O

B B or O

AB (UNIVERSAL RECIPIENT) A, B, AB, or O

O (UNIVERSAL DONOR) O

The pedigree diagram below shows the blood groups of The pedigree diagram below shows the blood groups of individuals of a family. The blood groups are indicated inside individuals of a family. The blood groups are indicated inside the circle or square. The blood groups of individuals W and X the circle or square. The blood groups of individuals W and X are not indicated.are not indicated.

Blood group O

W

X

Blood Group A Blood

group B

Blood group O Key:

Male

Female

Write down al the possible genotypes of individuals:[a] W[b] X (8)

(a)W = AB (IAIB)

(b)AO (IAi)

X = AO (IAi)

OO (ii)

Haemophilia is a blood clotting disorder. Explain Haemophilia is a blood clotting disorder. Explain why mainly males suffer from this disorder.why mainly males suffer from this disorder.

(4) (4) • It is a sex-linked disease caused by a

recessive allele carried on the X chromosome

• Males need only one recessive allele to have the disease because

• they have XY combination,

• while females have to have both recessive alleles to have haemophilia

• because they have an XX combination any (4)

DIHYBRID CROSSESDIHYBRID CROSSESLet R = gene for round seeds r = gene for wrinkled seeds Let Y = gene for yellow seeds y = gene for green seeds

If a Round, yellow seed is crossed with a wrinkled green seed: Genotype of parents (P1) RRYY x rryy meiosis Gametes RY RY ry ry Genotype of offspring (F1) RrYy Phenotype of offspring: All Round, Yellow seeds

Genotype of parents (P2) RrYy x RrYy meiosis Gametes RY Ry rY ry RY Ry rY ry Genotypes of the offspring (F2)

GAMETES RY Ry rY ry

RY Ry rY ry

Phenotype of offspring (F2): Round Yellow: ……… ……… Round Green: ............ Wrinkled Yellow: ……..... Wrinkled Green: ……….

RRYY RRYy RrYY RrYy

RrYY RrYy rrYY rrYy

RRYy RRyy RrYy Rryy

RrYy Rryy rrYy rryy

9

331

Polygenic inheritancePolygenic inheritance• Some phenotypes determined by Some phenotypes determined by

additive effects of 2 or more genes additive effects of 2 or more genes on a single characteron a single character– phenotypes on a continuumphenotypes on a continuum– human traitshuman traits

•skin colorskin color

•heightheight

•weightweight

•eye coloreye color

• intelligenceintelligence

•behaviorsbehaviors

Polygenic inheritancePolygenic inheritance

ALBINISMALBINISMThe woman must be Aa (because parents were aa x AA or aa x Aa)

Albino man normal woman X aa Aa all a sperms x ½ A eggs ½ a ½ Aa ½ aa Normal children Albino children

AlbinismAlbinismJohnny & Edgar Winter

albinoAfricans

DOWN’S SYNDROMEDOWN’S SYNDROME

DOWN’S SYNDROMEDOWN’S SYNDROME

• Individuals with Down syndrome tend to Individuals with Down syndrome tend to have a lower-than-average cognitive have a lower-than-average cognitive ability, often ranging from mild to ability, often ranging from mild to moderate disabilities. moderate disabilities.

• A small number have severe to profound A small number have severe to profound mental disability. The average IQ of mental disability. The average IQ of children with Down syndrome is around children with Down syndrome is around 50, compared to normal children with an 50, compared to normal children with an IQ of 100.IQ of 100.

• abnormally small chinabnormally small chin

• poor muscle tonepoor muscle tone

• a flat nasal bridgea flat nasal bridge

• protruding tongue (due to small oral cavity, protruding tongue (due to small oral cavity,

• short neck,short neck,

• Mental retardation in the mild ( in the mild (IQ 50–70) to moderate (IQ 50–70) to moderate (IQ 35–50) range.35–50) range.

• They also may have a broad head and a very round face.They also may have a broad head and a very round face.

• Language skills show a difference between Language skills show a difference between understanding speech and expressing speech, and understanding speech and expressing speech, and commonly individuals with Down syndrome commonly individuals with Down syndrome

Nature vs. nurtureNature vs. nurture• Phenotype is controlled by Phenotype is controlled by

both environment & genesboth environment & genes

Color of Hydrangea flowers is influenced by soil pH

Human skin color is influenced by both genetics & environmental conditions

Coat color in arctic fox influenced by heat sensitive alleles

Non Inherited variationsNon Inherited variations

• Birth Defects also called congenital Birth Defects also called congenital disordersdisorders due to factors affecting foetal due to factors affecting foetal development, such as radiation, heat, development, such as radiation, heat, chemicals (booze, smoking), infectious chemicals (booze, smoking), infectious agents or maternal disease (e.g., measles)agents or maternal disease (e.g., measles)

• Teratogen:Teratogen: “monster” “born” “monster” “born”

ENVIRONMENTAL VARIATIONS

Inherited VariationsInherited Variations• MutationsMutationsA mutation occurswhen the A mutation occurswhen the

order of nucleotides in the order of nucleotides in the D.N.A. is changed.D.N.A. is changed.

X-rays, excessive exposure X-rays, excessive exposure to the sun’s heat, to the sun’s heat, exposure to harmful exposure to harmful chemicals, radiation form chemicals, radiation form nuclear bomb explosions nuclear bomb explosions are some of the causes of are some of the causes of mutated genes.mutated genes.

The offspring will inherit the The offspring will inherit the mutated genemutated gene

HybridisationHybridisation

Genetically modified (GM) Genetically modified (GM) foodsfoods

• Genetically modified organisms have Genetically modified organisms have had specific changes introduced into had specific changes introduced into their DNA by genetic engineering, their DNA by genetic engineering,

• unlike similar food organisms which unlike similar food organisms which have been modified from their wild have been modified from their wild ancestors through selective breeding ancestors through selective breeding (plant breeding and animal breeding) (plant breeding and animal breeding) or mutation breeding. or mutation breeding.

• GM foods were first put on the GM foods were first put on the market in the early 1990s. market in the early 1990s.

GM foodsGM foods

• GM foods have been modifies to: GM foods have been modifies to: increase the crop yieldincrease the crop yield; ;

• make crops resistant to herbicides make crops resistant to herbicides (so (so that weeds can be eliminated); that weeds can be eliminated); resistance to insectsresistance to insects which may eat the which may eat the crop; crop;

• production of specific nutrientsproduction of specific nutrients (like (like vitamins); vitamins);

• produce produce drought-resistance cropsdrought-resistance crops;;• improve the improve the tastetaste of certain foods; of certain foods;

GM FOODS – the positivesGM FOODS – the positives

GM FOODS – the negativesGM FOODS – the negatives

• Critics have objected to GM foods on several Critics have objected to GM foods on several grounds, including perceived grounds, including perceived safety issues safety issues (may cause diseases)(may cause diseases), , ecological ecological concerns (genes from GM foods may concerns (genes from GM foods may mix with non-GM foods and cause mix with non-GM foods and cause unfvourable changes in crops) unfvourable changes in crops) and and

• economic concernseconomic concerns raised by the fact that raised by the fact that these organisms are these organisms are subject to subject to intellectual property law (premium on intellectual property law (premium on price for these seeds)price for these seeds)..

Human GenomeHuman Genome• The human genome is the The human genome is the genome

of of Homo sapiens, which is stored , which is stored on 23 chromosome pairs. Twenty-on 23 chromosome pairs. Twenty-two of these are two of these are autosomal chromosome pairs, , while the remaining pair is while the remaining pair is sex-determining. The . The haploid human genome occupies a total of human genome occupies a total of just over just over 3 billion 3 billion DNA base pairs. . The The Human Genome Project (HGP) (HGP) produced a produced a reference sequence of of the euchromatic human genome, the euchromatic human genome, which is used worldwide in which is used worldwide in biomedical sciences.biomedical sciences.

Human GenomeHuman Genome

• The haploid human genome contains The haploid human genome contains ca. 23,000 protein-coding genesca. 23,000 protein-coding genes, , far fewer than had been expected far fewer than had been expected before its sequencing. In fact, only before its sequencing. In fact, only about about 1.5% of the genome codes for 1.5% of the genome codes for proteinsproteins, while the rest consists of , while the rest consists of non-coding RNA genes, regulatory non-coding RNA genes, regulatory sequences, introns, and (controversially sequences, introns, and (controversially named) "junk" DNA. named) "junk" DNA.

STEM CELLSSTEM CELLS

• Stem cells are cells found in all multi Stem cells are cells found in all multi cellular organisms. They are cellular organisms. They are characterized by the characterized by the ability to ability to renew themselves through renew themselves through mitotic cell division and mitotic cell division and differentiate into a diverse range differentiate into a diverse range of specialized cell types.of specialized cell types.

• The two broad types of mammalian stem The two broad types of mammalian stem cellscells are: are:

• embryonic stem cellsembryonic stem cells that are isolated from that are isolated from the inner cell mass of blastocysts, and the inner cell mass of blastocysts, and

• adult stem cells that are found in adult adult stem cells that are found in adult tissuestissues. .

• In a developing embryo, In a developing embryo, stem cells can stem cells can differentiate into all of the specialized differentiate into all of the specialized embryonic tissues.embryonic tissues. In adult organisms, stem In adult organisms, stem cells and progenitor cells act as a repair cells and progenitor cells act as a repair system for the body, replenishing specialized system for the body, replenishing specialized cells, but also maintain the normal turnover of cells, but also maintain the normal turnover of regenerative organs, such as blood, skin, or regenerative organs, such as blood, skin, or intestinal tissues.intestinal tissues.

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