Chromosome Theory of Inheritance

Chromosome Theory Today’s understanding: Genes, which determine genetic traits, are located on chromosomes Today’s understanding: Genes, which determine genetic traits, are located on chromosomes Historical Evidence: Historical Evidence: Sutton Sutton Morgan Morgan Bridges Bridges

X – Linked Traits HUMAN EXAMPLE Autosomal Inheritance Genes for these traits on #1  22 Genes for these traits on #1  22 Both ♂ & ♀ have two genes for every trait Both ♂ & ♀ have two genes for every trait X-linked Inheritance X- Linked trait – traits whose gene is located on the “X” chromosome, therefore X- Linked trait – traits whose gene is located on the “X” chromosome, therefore Females (XX) have two genes Females (XX) have two genes Males (XY) only have one…… Males (XY) only have one……

Human Sex Chromosomes

Some X-linked Traits H = normal blood clotting h = hemophilia D = normal muscular development d = muscular dystrophy C = normal color vision c = color blindedness

Possible Genotypes of BIO SCI230 ♀ C C † † C C † † C c † † c c † † c c † † genotype phenotype

Possible Genotypes of SCI 230 ♀ C C † † C C † † C c † † c c † † c c † † genotype Homozygous Dominant phenotype Normal Color Vision

Possible Genotypes of SCI 230 ♀ C C † † C C † † C c † † c c † † c c † † genotype Homozygous Dominant heterozygous phenotype Normal Color Vision

Possible Genotypes of SCI 230 ♀ C C † † C C † † C c † † c c † † c c † † genotype Homozygous Dominant heterozygous phenotype Normal Color Vision Normal but “carrier”

Possible Genotypes of SCI 230 ♀ C C † † C C † † C c † † c c † † c c † † genotype Homozygous Dominant heterozygousHomozyg.Recessive phenotype Normal Color Vision Normal but “carrier”

Possible Genotypes of SCI 230 ♀ C C † † C C † † C c † † c c † † c c † † genotype Homozygous Dominant heterozygousHomozyg.Recessive phenotype Normal Color Vision Normal but “carrier” Color blind!

Possible Genotypes of SCI 230 ♂ C † γ C † γ c † γ c † γ Genotype phenotype

Possible Genotypes of SCI 230 ♂ C † γ C † γ c † γ c † γ Genotypehemizygousdominant phenotype

Possible Genotypes of SCI 230 ♂ C † γ C † γ c † γ c † γ Genotypehemizygousdominant phenotype normal color vision

Possible Genotypes of SCI 230 ♂ C † γ C † γ c † γ c † γ Genotypehemizygousdominanthemizygousrecessive phenotype normal color vision

Possible Genotypes of SCI 230 ♂ C † γ C † γ c † γ c † γ Genotypehemizygousdominanthemizygousrecessive phenotype normal color vision Color blind!

HINT (for working problems w X-linkage) RECORD THE SEX CHROMSOMES of BOTH PARENTS !!

Sample Problem A carrier for hemophilia marries a normal male. 1. What is the probability that their daughter is a hemophiliac? 2. What is the probability that their son is a hemophiliac? 3. What is the probability that their daughter is a carrier? 4. What is the probability that their son is a carrier?