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KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. Objectives. Students will be able to: Relate dominant-recessive patterns of inheritance in autosomal chromosomes to genetic disorders. Describe patterns of inheritance in sex-linked traits.
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KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.
Objectives • Students will be able to: • Relate dominant-recessive patterns of inheritance in autosomal chromosomes to genetic disorders. • Describe patterns of inheritance in sex-linked traits.
Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture.
(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.
Female mammals have an XX genotype. • Expression of sex-linked genes is similar to autosomal genes in females. • X chromosome inactivation randomly “turns off” one X chromosome.
Review • How are dominant-recessive patterns of inheritance in autosomal chromosomes related to genetic disorders? • What are the patterns of sex-linked traits? • How are Mendel’s observations related to genes on autosomes? • Why are males more likely than females to have sex-linked genetic disorders? • How are autosomal traits, including recessive genetic disorders that are carried in a population, related to Mendel’s observations of heredity? • Describe how sex-linked genes are expressed differently in males and in females. • How might a scientist determine whether a trait is sex-linked by observing the offspring of several genetic crosses? • How is the expression of sex-linked genes both similar to and different from the expression of autosomal genes? • Scientists hypothesize that over millions of years, the Y chromosome has lost genes to the X chromosome. During what stages of meiosis might the Y chromosome have transferred genes to the X chromosome? Explain.