Question

In: Biology

A black haired mouse was crossed to a hairless mouse. Since it lacked hair, it was...

A black haired mouse was crossed to a hairless mouse. Since it lacked hair, it was impossible to tell if its hair was black or brown. All the F1 progeny had black hair. When these F1 progeny were mated among themselves (to obtain the F2 generation), 96 were black, 43 were hairless, and 30 were brown

(a) What is the approximate observed phenotypic ratio of these offspring? (1 points)

(b) Explain the pattern of inheritance observed here (what are the genotypes that correspond to the observed phenotypes). Assume that the two genes involved are called A and B. (4 points)

(c) What are the actual genotypes of the original parents? (2 points)

(d) What are the actual genotypes of the F1 black haired mice? (1 point)

(e) What are the actual genotypes and phenotypes of the F2 black, hairless, and brown mice, respectively (list all genotypes and phenotypes)? (5 points)

Expert Solution

a) 96 were black, 43 were hairless, and 30 were brown.

total number of progeny= 96+43+30=169

in a dihybrid cross, there are 16 possibilities.

so divide the total number of progenies with 16

169/16=10.5625

the observed ratio is

Black: brown: hairless= 96:30:43=9.1:2.84:4.1

( to simplify the ratio divide with 10.5625)

Black: brown: hairless= 9.1:2.84:4.1

b) all the F1 progenies are black-haired, so black hair colour and presence of hair are dominant traits, but if the mice is homozygous for the absence of hair ( absence of hair is homozygous recessive), thephenotype at the hair colour locus is not expressed so this shows recessive epistasis, epistatic gene is responsible for the presence of hair.

c) let the alleles be B-black, b- brown, H- hairs, h- hairless

all the F1 progenies are black, haired so black and hairs are dominant alleles, in the F2 there are brown progenies so the genotype of the black, haired parent is BBHH and genotype of the hairless parent is bbhh

d) BBHH * bbhh

BbHh

Genotype of the F1 is BbHh.

e) BbHh * BbHh

	BH	Bh	bH	bh
BH	BBHH (black, haired)	BBHh(black, haired)	BbHH(black, haired)	BbHh(black, haired)
Bh	BBHh (black, haired)	BBhh (hairless)	BbHh(black, haired)	Bbhh (hairless)
bH	BbHH(black, haired)	BbHh(black, haired)	bbHH (brown, haired)	bbHh (brown, haired)
bh	BbHh(black, haired)	Bbhh(hairless)	bbHh (brown, haired)	bbhh(hairless)

genotype of black, haired are

BBHH, BbHH, BBHh, BbHh

genotype of hairless are

Bbhh, BBhh, bbhh.

genotype of brown haired are

bbHh, bbHH

gladiator answered 9 months ago

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