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7.1 Chromosomes and Phenotype KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. 7.1 Chromosomes and Phenotype 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. 7.1 Chromosomes and Phenotype Two copies of each autosomal gene affect phenotype. • Mendel studied autosomal gene traits, like hair texture. 7.1 Chromosomes and Phenotype • 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. (dominant) 7.1 Chromosomes and Phenotype 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. 7.1 Chromosomes and Phenotype • Male mammals have an XY genotype. – All of a male’s sexlinked genes are expressed. – Males have no second copies of sex-linked genes. 7.1 Chromosomes and Phenotype • 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. 7.1 Chromosomes and Phenotype • 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.