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Genes and Chromosomes

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Genes Code for Proteins

One gene: One enzime

One gene : Onepolypeptide

or RNA

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• Dominanceis explainedby the

propertiesof mutantproteins

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utations in thesame gene cannot

complement

utations: !oos offunction or gain of

function

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Recombinationocurrs by

physicalexchangeof DNA

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•  "he code genetic is triplet

• #$ery se%uence hasthree possiblereading frames

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&e$eral

processes arere%uired toexpress theprotein productof a gene

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• Proteins are trans acting

• &ites on DNA are cis acting

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 "'# (N"#RR)P"#D G#N#

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• &ome genes possess only one o fe*introns

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&ome DNA se%uences code for more thanone polypeptide

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&ome exons can be e%uated *ith proteinfunctional domains

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The Content of the Genome:

The genomeThe transcriptome

The proteome

The interactome

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+igure ,-.,/: A point mutation that a0ects a restriction site is detectedby a di0erence in restriction fragment lengths.

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 Individual Genomes Show Extensive

Variation

+igure ,-.,1: A restrictionpolymorphism can be used as a

genetic mar2er to measurerecombination distance from a

phenotypic mar2er.

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+igure ,-.,3: (f a restriction mar2er is associated *ith a phenotypiccharacteristic4 the restriction site must be located near the gene for the

phenotype.

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 Eukarotic Genomes Contain !oth

"onrepetitive and #epetitive $"% Se&uences

•  % large part of

moderatelrepetitive $"% ma

'e made up of

transposons(+igure ,-.,-: "he proportions of di0erentse%uence components $ary in eu2aryotic

genomes.

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 Some )rganelles *ave $"%

• +itochondria and chloroplasts

have genomes that show non-

Mendelian inheritance(

Tpicall the are maternally

inherited(• )rganelle genomes ma

undergo somatic segregation in

plants(

+igure ,-./,: DNA from the sperm entersthe oocyte to form the male pronucleus in

the egg4 but all the mitochondria are

pro$ided by the oocyte.

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  )rganelle Genomes %re Circular $"%s

That Encode )rganelle ,roteins

• )rganelle genomes are usuall -'ut not alwas.

circular molecules of $"%(

 / Mitochondrial DNA (mtDNA)

 / Chloroplast DNA (cpDNA or  ctDNA)• )rganelle genomes encode some0 'ut not all0 of

the proteins used in the organelle(

+igure ,-.//: itochondrialgenomes ha$e genes

encoding 5mostly complex (6(78 proteins4 rRNAs4 and

tRNAs.

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 )rganelle Genomes %re Circular $"%s

That Encode )rganelle ,roteins

+igure ,-./9: 'uman mitochondrialDNA has 99 tRNA genes4 t*o rRNA

genes4 and /1 proteincodingregions.

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  The Chloroplast Genome Encodes +an

,roteins and #"%s

• Chloroplast genomes var in si1e0 'ut are large enoughto encode 23 to 433 proteins as well as r#"%s and

t#"%s(

+igure ,-./3: "he chloroplastgenome in land plants

encodes 3 rRNAs4 1, tRNAs4and ;

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• Genome se%uences and genenumbers

+igure ,

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 ,rokarotic Gene "um'ers #ange )ver an

)rder of +agnitude

• The minimum num'er of

genes for a parasitic

prokarote is a'out 2335

for a free6living

nonparasitic prokarote itis a'out 4233(

+igure ,

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+igure ,

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Total Gene "um'er Is 7nown for Several

Eukarotes

• There are 8333 genes in east5 94033 in a nematode

worm5 40333 in a fl5 920333 in the small plant

 Arabidopsis5 and pro'a'l 930333 to 920333 in mice and

humans(

+igure ,

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+igure ,

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 Total Gene "um'er Is 7nown for Several

Eukarotes

+igure ,

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*ow +an $ifferent Tpes of Genes %re

There;

• The sum of the num'er of uni&ue genes and the num'er

of gene families is an estimate of the num'er of tpes of

genes(

+igure ,

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 *ow +an $ifferent Tpes of Genes %re

There;

• orthologous genes

(orthologs) – #elated

genes in different

species(

• The minimum si1e ofthe proteome can 'e

estimated from the

num'er of tpes of

genes( 

+igure ,

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The *uman Genome *as 2= of each gene0 so genes -exons

plus introns. comprise >92= of the genome(• The human genome has 930333 to 920333 genes(

+igure ,

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 The *uman Genome *as

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  The *uman Genome *as 83= of human genes are alternativel spliced(

• ?p to @3= of the alternative splices change protein

se&uence0 so the proteome has >230333 to 830333

mem'ers(

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*ow %re Genes and )ther Se&uences

$istri'uted in the Genome;

• #epeated se&uences -present in more than one cop.

account for A23= of the human genome(

• The great 'ulk of repeated se&uences consists of copies

of nonfunctional transposons(

• There are man duplications

of large chromosome regions( 

+igure ,

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The B Chromosome *as Several

+ale6Specific Genes

• The B chromosome has >83 genes that are expressed

specificall in the testis(

• The male6specific genes are present in multiple copies in

repeated chromosomal segments(

• Gene conversion 'etween multiple copies allows the

active genes to 'e maintained during evolution(

+igure ,

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*ow +an Genes %re Essential;

• "ot all genes areessential( In east andflies0 deletions of 23= ofthe genes have

detecta'le effects(• Dhen two or more genesare redundant0 amutation in an one ofthem ma not have

detecta'le effects(

+igure ,

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 *ow +an Genes %re Essential;

• De do not full understand the persistence of genes that

are apparentl dispensa'le in the genome(

+igure ,

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 %'out 430333 Genes %re Expressed at

Didel $iffering evels in a Eukarotic Cell

• m#"%s expressed at low levels overlap extensivelwhen different cell tpes are compared( / housekeeping gene / % gene that is -theoreticall.

expressed in all cells 'ecause it provides 'asic functions

needed for sustenance of all cell tpes(• The a'undantl expressed m#"%s are usuall

specific for the cell tpe(

 / luxury gene / % gene encoding a speciali1ed function0

-usuall. snthesi1ed in large amounts in particular cell

tpes(

• >430333 expressed genes ma 'e common to most

cell tpes of a multicellular eukarote(

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8(43 Expressed Gene "um'er Can !e

+easured En +asse

• $"% microarra technolog allows detailed comparisons

of related animal cells to determine -for example. the

differences in expression 'etween a normal cell and a

cancer cell(

+igure ,

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• Clusters and #epeats

• gene family

• pseudogenes

• gene cluster  

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(4 Introduction

• satellite DNA  – $"% that consists of man

tandem repeats -identical or related. of a short

'asic repeating unit(

• minisatellite  – $"%s consisting of tandemlrepeated copies of a short repeating se&uence0 with

more repeat copies than a microsatellite 'ut fewer

than a satellite(

 / The length of the repeating unit is measured in tens of 'asepairs(

 / The num'er of repeats varies 'etween individual genomes( 

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?ne&ual Crossing )ver #earranges Gene

Clusters

• Dhen a genome contains a cluster of genes with

related se&uences0 mispairing 'etween

nonallelic loci can cause une&ual crossing over(

 / This produces a deletion in one recom'inantchromosome and a corresponding duplication in the

other(

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?ne&ual Crossing )ver #earranges Gene

Clusters

+igure ,F.,3: Gene number can be changed by une%ual crossing o$er.

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?ne&ual Crossing )ver #earranges Gene

Clusters

• $ifferent thalassemias are

caused ' various deletions

that eliminate F6 or 6glo'in

genes( / The severit of the disease

depends on the individual

deletion(

+igure ,F.,-: thalassemiasresult from $arious deletionsin the globin gene cluster.

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+ammalian Satellites Consist of

*ierarchical #epeats

+igure ,F./F: "he alignment of eighthrepeats sho*s that each %uarterrepeat consists of an and a half.

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+inisatellites %re ?seful for Genetic

+apping

• The variation 'etween microsatellites or minisatellites

in individual genomes can 'e used to identif heredit

une&uivocall ' showing that 23= of the 'ands in an

individual are inherited from a particular parent(

• variale numer tandem repeat (!N"#)  – Ver shortrepeated se&uences0 including microsatellites and

minisatellites(

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+inisatellites %re ?seful for Genetic

+apping

+igure ,F.9,: Alleles may di0erby number of repeats at a

minisatellite locus4 so digestiongenerates restriction fragments

that di0er in length.

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Chromosomes

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• Centromere

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•  "elomeres

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• Nucleosome

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 Dos copias

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 "etramero '1'3

Dimero '9A'9>

p

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