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Transcript
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. • Genetic traits depend on dominant and recessive alleles • Other factors affect Phenotypes – Which chromosome allele is located on – Sex chromosome – Autosomal chromosome • Mendel studied autosomal gene traits, like hair texture. 7.1 Chromosomes and Phenotype • Sexually reproducing organisms have 2 copies of each gene, one from each parent – Both chromosomes have same gene, different alleles Ex. Purple flower vs White flower 7.1 Chromosomes and Phenotype • Mendel’s rules of inheritance apply to autosomal genetic disorders. – They are either recessive or dominant • One recessive disorder is Cystic Fibrosis – Is a disease that causes excessive production of mucus that causes blockage of pancreatic ducts, intestines, and bronchi, it is fatal – A heterozygote for a recessive disorder is a carrier. (dominant) 7.1 Chromosomes and Phenotype • Dominant disorders are less common – Huntingtons disease affects the nervous system, specifically causing brain cells to break down. It occurs in adulthood, and is fatal. • Since it occurs in adulthood someone can pass it on to there children, even before they show symptoms. 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.
