My_Ch15_lecture(2009030423481120)

My_Ch15_lecture(2009030423481120) - Chapter 15Chromosomes...

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Chapter 15—Chromosomes & Inheritance Purpose —to understand the chromosomal basis of inheritance, linkage, x-linked inheritance, and errors in chromosomal inheritance. What you MUST know in Ch 15: Linkage Inheritance of sex-linked genes X-inactivation Nondisjunction Aneuploidy Chromosome theory of inheritance—Mendelian genes have specific loci on chromosomes, chromosomes undergo segregation and independent assortment Thomas Morgan discovered that there were genes located on the X chromosome = sex-linked genes (different than “linked genes” above). (pgs 261-264) Fruit flies (Drosophila melanogaster) o Only 4 pairs of chromosomes o Females are XX, Males are XY o Mutant phenotype of white eyes only showed up in males (wild type “normal” = red eyes) o Gene for eye color is on X chromosome o Males have one X chromosome; if it has the mutant allele, it will have white eyes o Females must have 2 X chromosomes, both with the mutant allele to have white eyes (not possible in his experiment) Punnett square for sex-linked inheritance (= X-linked):
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(pages 269-270; Fig 15.9 for various possibilities of sex- linked inheritance) Carrier female & normal male: X * X X Y X * = X chromosome with abnormal gene X * X = carrier female X * Y = affected male, with the disorder XX, XY = normal offspring If a carrier female mates with a male with the trait, there is a 50% chance that each child will have the trait, regardless of sex (Fig. 15.9) A carrier male (even if mother is normal) will pass the abnormal allele to all of his daughters (X * ) so they will be carriers, but not to his sons (Y).
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