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KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. Review-Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture. BUT Patterns of inheritance are often complex!. (dominant).
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KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.
Review-Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture. • BUT Patterns of inheritance are often complex!
(dominant) • Mendel’s rules of inheritance apply to autosomal genetic disorders. • A heterozygote for a recessive disorder is a carrier. • Disorders caused by dominant alleles are uncommon.
Males and females can differ in sex-linked traits. • Genes on sex chromosomes are called sex-linked genes. • Y chromosome genes in mammals are responsible for male characteristics. • X chromosome genes in mammals affect many traits.
Male mammals have an XY genotype. • All of a male’s sex-linked genes are expressed. • Males have no second copies of sex-linked genes.
(1).X-linked traits or sex-linked traits. Studied by American Scientist-Thomas Hunt Morgan studied eye color of Drosophila melanogasta –fruit fly. • A pattern of inheritance when traits are controlled on the sex chromosome, not on the autosomes (#1-22). • If a male inherits the recessive trait on the x chromosome, the recessive trait will always be expressed. • The Y chromosome has no corresponding allele for an x-linked trait. ( It is not there!) • Two examples in humans are : Hemophilia and color blindness
Female mammals have an XX genotype. • X chromosome inactivation randomly “turns off” one X chromosome which results in two types of cells-females can be black, orange, and white. X-white (both males and females), X0, orange, Xo- black