Lecture 8 - with hypothesis that white eyes is a sex-linked...

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Biology 313 Lecture 8 Sept 10, 2010
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QUIZ 2: Dihybrid Cross
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4.2 Sex-Linkage Sex-linkage: one reason why a (9:3:3:1) ratio is not obtained in the F2 of some crosses Sex-linked characteristics are determined by genes on the sex chromosomes Genes on the X chromosome determine X- linked characteristics Genes on the Y determine Y-linked characteristics
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Drosophila is a model genetic organism 2n = 8 5% of human DNA content
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TH Morgan A rare white-eyed fly was found in his colony of red-eyed flies. How did it arise? Step one: study inheritance of the eye-color trait.
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To explain the strange skewing of sex in the F2, Morgan hypothesized that white is X-linked recessive (X w )
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DO THE RECIPROCAL CROSS: What genotypes and phenotypes are expected in the F1 and F2? (see Figure 12b) Morgan’s data are consistent
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Unformatted text preview: with hypothesis that white eyes is a sex-linked trait Eye color anomalies in Drosophila crosses Calvin Bridges (Morgan student) found exceptional progeny in crosses of some Dros. strains: red-eyed males and white-eyed females when it was not expected Explanation: nondisjunction These experiments provided definitive evidence that eye color genes are sex-linked and that genes reside on chromosomes. Concept requires knowledge of sex determination in Drosophila: Bridges figured this out Bridges generated flies with different numbers of sex chromosomes and autosomes He discovered that sex is determined by the X: autosome ratio (X: A ratio) Sex determination in Drosophila: genic balance mechanism VEISHEA PARADE 2008 SNOW!...
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This note was uploaded on 10/06/2011 for the course BIO 313 taught by Professor Rodermel during the Spring '11 term at Iowa State.

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Lecture 8 - with hypothesis that white eyes is a sex-linked...

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