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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