Why do females show an intermediate phenotype? What are the expected phenotypic

Question

Why do females show an intermediate phenotype? What are the expected phenotypic ratios in F1 generation? What are the expected results in F2 generation?

2. Bar eye in Drosophila is X-linked and exhibits incomplete dominance. Wild-type females have an s have an average of 59 facets. average of 810 facets in the eye, while homozygous Bar female . Males have either wild- Heterozygous females have a kidney-shaped eye with an average of 447 facets type shaped eyes with about 810 facets or Bar eyes with about 60 facets. a. Why do An autosomal recessive a red eyes is mated to a male wth normal-shaped but purple eyes. b. Wh C. if one of the Fi males is mated to an F, female, what are the expected results in the Fz generation? Show your work. 13 pts) show an intermediate phenotype? (1 pt) llele, purple, results in purple eyes when homozygous. A female with Bar but at are the expected phenotypic ratios in the Fi generation? Show your work/reasoning. (3 pts) a. The Manx breed of cat has no tail or a very short tail. the litter size is reduced, some of the kit manyanx cats have been found, despite more than a century of interest by cat breeders. When two Manx cats are bred to each oth tens have no tails, and some have a full-length tail. Among es, tailless offspring are about twice as common as kittens with a full tail. No true- such crosses, e ecovide an explanation consistent with these data that explains why no true-breeding tailless Manx a n addition to being talilless, the Manx breed is often prone to skalotl have been found. (1 pt) r noorly formed soinal col

Explanation / Answer

As mentioned in the question itself, bar linked eyes show incomplete dominance. Incomplete dominance is when the dominant allele is not able to completely mask the effect of the recessive allele. Thus in the case of heterozygous females, it results in an intermediate phenotype. A female with bar eyes and red coloured will have bar eye allele on both it’s X chromosome due to homozygous condition and either dominant homozygous colour allele or heterozygous colour alleles. As bar eye allele is X-linked, for males to have normal eyes, the gene should be absent in them. Also as the male has purple eyes, it will have homozygous recessive colour allele. Now in F1 generation, from female, an allele for bar eyes and a dominant allele of colour can be inherited. And from male, no allele for bar eye and a recessive allele for colour will be inherited, resulting in male offspring having bar eyes (due to hemizygous condition) and red eyes and female offspring being heterozygous with kidney-shaped eyes and red coloured. If a recessive colour gene was inherited from female, male offspring would have bar-eyes (due to hemizygous condition) and purple eye whereas female shall have kidney-shaped eyes due to heterozygous condition and purple eyes due to the homozygous condition. The ratio of phenotypes can be stated as follows – Male offspring with bar eyes and red eyes – the probability of inheriting dominant colour eye allele from mother * probability of inheriting Y chromosome from father = 3/4 * 1/2 = 3/8 Female offspring with kidney-shaped eyes and red eyes - probability of inheriting dominant colour eye allele from mother * probability of inheriting X chromosome from father = 3/4 * 1/2 = 3/8 Male offspring with bar eyes and purple eyes - – the probability of inheriting recessive colour eye allele from mother * probability of inheriting Y chromosome from father = 1/4 * 1/2 = 1/8 Female offspring with kidney-shaped eyes and purple eyes - the probability of inheriting recessive colour eye allele from mother * probability of inheriting X chromosome from father = 1/4 * 1/2 = 1/8 If one of the males of F1 generation is crossed with one the females in F1 generation, the offspring, if male, will inherit either recessive colour allele from father or dominant colour allele from father and dominant colour allele from mother or recessive colour allele. Also, the X-chromosome from mother may or may not contain bar eye allele. Therefore, the possible phenotypes will be bar eye + purple or bar eye + red. Offspring if female, will receive X chromosome from father with bar eye gene linked and recessive/dominant colour gene. And from mother, it will inherit either dominant/recessive colour allele. Also, the X-chromosome from mother may or may not contain bar eye allele. Hence, the possible phenotypes for female offspring would be – bar eye + red, bar eye + purple, kidney eye + red, kidney eye + purple.

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