Chromosome Chromosome Theory of Theory of

InheritanceInheritance

Chromosome TheoryChromosome Theory

Today’s understanding:Today’s understanding:Genes, which determine genetic Genes, which determine genetic traits, are located on chromosomestraits, are located on chromosomes

Historical Evidence:Historical Evidence: SuttonSutton MorganMorgan BridgesBridges

X – Linked Traits X – Linked Traits HUMAN EXAMPLEHUMAN EXAMPLE

Autosomal InheritanceAutosomal Inheritance Genes for these traits on #1Genes for these traits on #1 22 22 Both ♂ & ♀ have two genes for every Both ♂ & ♀ have two genes for every

traittrait

X-linked InheritanceX-linked Inheritance X- Linked traitX- Linked trait – traits whose gene is – traits whose gene is

located on the “X” chromosome, located on the “X” chromosome, thereforetherefore Females (XX) have two genesFemales (XX) have two genes Males (XY) only have one……Males (XY) only have one……

Human Sex Human Sex ChromosomesChromosomes

Some X-linked TraitsSome X-linked Traits

H = normal blood clottingH = normal blood clottinghh = hemophilia = hemophilia

D = normal muscular developmentD = normal muscular developmentd = muscular dystrophyd = muscular dystrophy

C = normal color visionC = normal color visioncc = color blindedness = color blindedness

Possible Genotypes of Possible Genotypes of BIO SCI230BIO SCI230 ♀ ♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype

phenotypephenotype

Possible Genotypes of Possible Genotypes of SCI 230SCI 230♀♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype HomozygoHomozygo

us us DominantDominant

phenotypephenotype Normal Normal Color Color VisionVision

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♀♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype HomozygoHomozygo

us us DominantDominant

heterozygoheterozygousus

phenotypephenotype Normal Normal Color Color VisionVision

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♀♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype HomozygoHomozygo

us us DominantDominant

heterozygoheterozygousus

phenotypephenotype Normal Normal Color Color VisionVision

Normal Normal but but

“carrier”“carrier”

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♀♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype HomozygoHomozygo

us us DominantDominant

heterozygoheterozygousus

HomozygHomozyg..

RecessivRecessivee

phenotypephenotype Normal Normal Color Color VisionVision

Normal Normal but but

“carrier”“carrier”

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♀♀

C CC C

† †† †C C cc

† †† † cc cc

† †† †genotypegenotype HomozygoHomozygo

us us DominantDominant

heterozygoheterozygousus

HomozygHomozyg..

RecessivRecessivee

phenotypephenotype Normal Normal Color Color VisionVision

Normal Normal but but

“carrier”“carrier”

Color Color blind!blind!

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♂♂

C C

† † γγ

cc

† † γγGenotypeGenotype

phenotypephenotype

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♂♂

C C

† † γγ

cc

† † γγGenotypeGenotype

hemizygoushemizygous

dominantdominant

phenotypephenotype

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♂♂

C C

† † γγ

cc

† † γγGenotypeGenotype

hemizygoushemizygous

dominantdominant

phenotypephenotype normal normal color visioncolor vision

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♂♂

C C

† † γγ

cc

† † γγGenotypeGenotype

hemizygoushemizygous

dominantdominanthemizygoushemizygous

recessiverecessive

phenotypephenotype normal normal color visioncolor vision

Possible Genotypes of Possible Genotypes of SCI 230 SCI 230 ♂♂

C C

† † γγ

cc

† † γγGenotypeGenotype

hemizygoushemizygous

dominantdominanthemizygoushemizygous

recessiverecessive

phenotypephenotype normal normal color visioncolor vision Color blindColor blind!!

HINTHINT(for working problems w X-(for working problems w X-

linkage)linkage)

RECORD THE SEX RECORD THE SEX CHROMSOMESCHROMSOMES

of BOTH PARENTS !! of BOTH PARENTS !!

Sample ProblemSample Problem

A carrier for hemophilia marries a A carrier for hemophilia marries a normal male.normal male.

1.1. What is the probability that their What is the probability that their daughter is a hemophiliac? daughter is a hemophiliac?

2.2. What is the probability that their What is the probability that their son is a hemophiliac?son is a hemophiliac?

3.3. What is the probability that their What is the probability that their daughter is a carrier?daughter is a carrier?

4.4. What is the probability that their What is the probability that their son is a carrier?son is a carrier?