A woman with Turner syndrome is found to be colorblind (X-linked recessive pheno

Question

A woman with Turner syndrome is found to be colorblind (X-linked recessive phenotype). Both her mother and her father have normal vision. a. Explain the simultaneous origin of Turner syndrome and colorblindness by the abnormal behavior of chromosomes at meiosis. b. Can your explanation distinguish whether the abnormal chromosome behavior occurred in the father or the mother? c. Can your explanation distinguish whether the abnormal chromosome behavior occurred at the first or second division of meiosis? d. Now assume that a colorblind Klinefelter man has parents with normal vision, and answer parts a, b, and c.

Explanation / Answer

In Turner syndrome, half of sex cromosomes are missing ( known as monosomy x) while normaly the other cromosome has same locus and possibly Dominating gene. With out the other cromosome, the possibility of colorblindness ( X linked resessive) becomes much greater ( 50,50) b) No, both parents have haploid genome and the error might have hapened in eiter one c) in meiosis II anaphase II when the strands are pulled to different sides of cell d) a)double XX +Y , the colorblind gene is resessive in XX and Y. or resessive in XX but domining Y only rules out the other resessive. d-b) no , same explanation as in I-b) d-c)X chromosome is retained because of a nondisjunction event during meiosis I (gametogenesis) or meiosis II in the female

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