Biology Forums - Study Force

1) In mice, black fur (B) is dominant over brown fur (b). Two black mice had only black offspring.
Which of the following offspring genotypes could result from the parental cross? Select all that apply.

Select one or more:

a.
BB

b.
Bb

c.
bb







2) In mice, black fur (B) is dominant over white fur (b).

A testcross was performed to determine the genotype of a black mouse. What is the genotype of the mouse that was testcrossed with the unknown black mouse?

#1

BB , Bb and bb

Black spur - B (dominant)

Brown spur - b (recessive)

BB - Black spur

Bb - Black spur

bb - Brown spur

Given that, 2 black mice have brown offspring.

Offspring has definitely genotype bb

This is possible only if both parent mice have genotype Bb.

Bb X Bb -----> BB , Bb and bb

#2

Black fur - B (dominant)

White Fur - b (recessive)

BB - Black fur

Bb - Black fur

bb - White fur

a)If any of the offspring have white fur, the parental black mouse genotype is homozygous

- Offspring with white fur has genotype bb

- It is possible only if there is b allele coming from both parents.

- If any of the offspring is white, parents with black fur should be genotype Bb. They can't be homozygous.

b) If all of the offspring have white fur, the parental black mouse genotype is homozygous

- Offspring with white fur has genotype bb

- Parents with black fur should be genotype Bb

- Option b is wrong

c) If all of the offspring have black fur, the parental white mouse genotype is heterozygous

- Offspring with black fur can have genotype BB or Bb

- White mouse genotype is always bb. It cannot be heterozygous. Option c is false.

d) If all of the offspring have black fur, the parental black mouse genotype is homozygous

- Offspring with black fur can have genotype BB or Bb.

- parental black mouse can be BB or Bb.

- If all offsprings are black, parents with black fur should have genotype BB. So they are homozygous.

Otherwise there is probability of having white offsprings.

thanks but can you help with this one as well thanks

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