5. In mouse, the tail shape gene is located on the X chromosome and has two alle

ID: 199419 • Letter: 5

Question

5. In mouse, the tail shape gene is located on the X chromosome and has two alleles Bent tail is completely dominant to straight tail. a. A straight-tailed female is mated with a bent-tailed male. i. Using any letter of your choosing, define your alleles and then state the genotypes of each of the parent mice? 1. straight-tailed female: 2. bent-tailed male: ii. What genotypes, corresponding phenotypes and phenotypic proportions will occur in the F1 generation? Hair color in mice is due to an autosomal gene with two alleles. Black hair (H) is dominant to brown hair (h). If two heterozygous mice are crossed, what are the phenotypes and phenotypic proportions of the progeny? b. The straight-tailed female and bent-tailed male (from part a) are both heterozygous for the coat color gene. c. What is the probability they have a progeny that is a bent-tailed female with brown hair? i. ii. What is/are the genotype(s) of the progeny? d. In mammals, which sex is more likely to suffer from X-linked recessive diseases and why?

Explanation / Answer

Bent tail = Dominant = XBXB or XBXb or XBY

Straight tail = Recessive = XbXb or XbY

Straight tailed female = XbXb

Bent tailed male = XBY

Black hair = Dominant = HH or Hh

Brown hair = Recessive = hh

Parental cross: Hh X Hh

Progeny = HH Hh Hh hh

Phenotypic ratio = 3 (Black) : 1 (Brown)

Straight tailed female with heterozygous black hair = XbXb Hh

Bent tailed male with heterozygous black hair = XBY Hh

Parental cross: XbXb Hh X XBY Hh

Gametes: (XbH)(Xbh) X (XBH)(XBh)(YH)(Yh)

Progeny: XBXbHH XBXbHh XbYHH XbYHh XBXbHh XBXbhh XbYHh XbYhh

Bent tailed female with brown hair = XBXBhh or XBXbhh

Probability = 1/8

In animals, male sex is more likely to suffer from an X-linked disorder. this is because males are heterozygous for X-chromosome. So, they exhibit mutant phenotype even if they contain a single recessive allele. Females are homozygous of X chromosome. So, they must contain two recessive alleles in order to exhibit mutant phenotype.

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5. In mouse, the tail shape gene is located on the X chromosome and has two alle

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