Chromosomal Basis of Chromosomal Basis of InheritanceInheritance

Tracing Heredity through InheritanceTracing Heredity through Inheritanceof Specific Chromosomesof Specific Chromosomes

Sex DeterminationSex Determination

Sex ChromosomesSex Chromosomes: homologous : homologous chromosomes that differ in size and chromosomes that differ in size and genetic composition between males and genetic composition between males and femalesfemales

Human Human

ChromosomeChromosome

XX YY

Size and Size and gene numbergene number

LargerLarger

2142 genes2142 genes

SmallerSmaller

326 genes326 genes

Genetic Genetic

CompositionComposition

Multiple genes Multiple genes unrelated unrelated

to genderto gender

Single gene influences Single gene influences gender: TDF = testis gender: TDF = testis

determining factordetermining factor

Sex DeterminationSex Determination

Autosome:Autosome: any chromosome that is not any chromosome that is not a sex chromosomea sex chromosome

Humans have 22 pairs of autosomesHumans have 22 pairs of autosomesand 1 pair of sex chromosomes and 1 pair of sex chromosomes

Human Karyotype showingHuman Karyotype showinghomologous chromosome pairshomologous chromosome pairs

Sex Determination Sex Determination

Female Male Female Male XX x XYXX x XY

Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring

X-linked Genes X-linked Genes Hemophilic Male Non-hemophilic Hemophilic Male Non-hemophilic Female Female (father is hemophilic)(father is hemophilic)

Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring

Terms Specific toTerms Specific toSex-linked GenesSex-linked Genes

FemalesFemales Homogametic: Homogametic: only X found only X found in gametes in gametes

Can be homozygous or Can be homozygous or heterozygous for traits on X-heterozygous for traits on X-chromosomechromosome

MalesMales Heterogametic: Heterogametic: either X or either X or Y in gametesY in gametes

Hemizygous for traits on the Hemizygous for traits on the X-chromosomeX-chromosome

Patterns of InheritancePatterns of Inheritance

• Autosomal DominantAutosomal Dominant

• Autosomal RecessiveAutosomal Recessive

• X-linked Dominant X-linked Dominant

• X-linked RecessiveX-linked Recessive

• Y-Linked InheritanceY-Linked Inheritance

Pedigree for Huntington’s Disease, Pedigree for Huntington’s Disease, an Autosomal Dominant Traitan Autosomal Dominant Trait

Pedigree for Albinism, an Autosomal Recessive TraitPedigree for Albinism, an Autosomal Recessive Trait

Pedigree for Colorblindness, Pedigree for Colorblindness, an X-linked Recessive Traitan X-linked Recessive Trait