Genes on the X Chromosome:
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Transcript of Genes on the X Chromosome:
Genes on the X Chromosome:
*Sex chromosomes*Autosomes
Example: In Drosophila and all mammalssex chromosomes designated as X and YXX=femaleXY=male
*1909 Thomas Hunt Morgan
II III IV
XX
XY
or
*X-linkage
X-linkage in Drosophila: white mutation (eyes)
Genes on the X Chromosome con’t:
Sex-limited Inheritance:*Sex-limited trait
*holandric genes: genes on the Y chromosome
*autosomal genesExample: milk production in mammals; L=lots, l=little
*Sex-influenced trait
Sex-influenced Inheritance:
Examples:*cleft palate in humans*horns in sheep *pattern baldness in
humans
Summary:Sex-linked on X or Y sex-chromosomeSex-limited all or none expression by sexSex-influenced genotype + sex determines phenotype
Phenotypic Expression:
*Penetrance
*Expressivity
Gene expression often governed by genotype and environment
If 9/10 of individuals carrying an allele express the trait, the trait is said to be 90% penetrant
*Onset of genetic expression
*Temperature