Transcript Document
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 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 Work the following problem: • Two parents, who both know their genotype, are carriers for albinism. They are both heterozygous. What is the chance that their children have albinism? 7.1 Chromosomes and Phenotype Work the following problem: • Huntington’s disease is a rare, but not uncommon, disease that is caused by a dominant allele. Suppose that two parents are crossed one that is heterozygous for Huntington’s and one that is homozygous recessive. What is the chance that their offspring will have Huntington’s disease? 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 • A male (XX) and a female (XY) mate – what is the chance that they have a male offspring? 7.1 Chromosomes and Phenotype Weird combinations have happened….. • Any combination (up to XXXXY) produces maleness. Males with more than one X are usually underdeveloped and sterile. • XXX and XO women are known, although in most cases they are sterile. 7.1 Chromosomes and Phenotype 7.1 Chromosomes and Phenotype 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.