Question

in mice, the ability to run normally requires a particular protein. if either of the mouses alleles for that gene is the normal allele (r) then the mouse can run normally and is called “running”. if both alleles are mutant (r), so that the mouse lacks the particular protein, it causes mice to run in circles. mice with this phenotype are called waltzing mice. albinism is also inherited. brown hair (b) is dominant over albino (b). for each of the following crosses, draw a punnett square and answer the questions. 1. cross a heterozygous running, heterozygous brown mouse with a heterozygous running, albino mouse. a. what is the probability that an offspring will be running brown? b. what is the probability that a mouse will be running albino? c. what is the probability that a mouse will be waltzing brown? d. what is the probability that a mouse will be waltzing albino?

Explanation:

Step1: Determine the genotypes of the parents

The first parent is heterozygous running (Rr) and heterozygous brown (Bb), so its genotype is RrBb. The second parent is heterozygous running (Rr) and albino (bb), so its genotype is Rrbb.

Step2: Determine the possible gametes

For the RrBb parent, the possible gametes are RB, Rb, rB, rb. For the Rrbb parent, the possible gametes are Rb, rb.

Step3: Create the Punnett - square

	RB	Rb	rB	rb
rb	RrBb	Rrbb	rrBb	rrbb

Step4: Calculate probabilities for each phenotype

a. Probability of running brown

Running requires at least one R allele (RR or Rr) and brown requires at least one B allele (BB or Bb). There are 6 out of 16 offspring with the genotypes RRBb, RrBb, so the probability is $\frac{6}{16}=\frac{3}{8}$.

b. Probability of running albino

Running requires at least one R allele (RR or Rr) and albino is bb. There are 6 out of 16 offspring with the genotypes RRbb, Rrbb, so the probability is $\frac{6}{16}=\frac{3}{8}$.

c. Probability of waltzing brown

Waltzing is rr and brown requires at least one B allele (BB or Bb). There are 2 out of 16 offspring with the genotype rrBb, so the probability is $\frac{2}{16}=\frac{1}{8}$.

d. Probability of waltzing albino

Waltzing is rr and albino is bb. There are 2 out of 16 offspring with the genotype rrbb, so the probability is $\frac{2}{16}=\frac{1}{8}$.

Answer:

a. $\frac{3}{8}$
b. $\frac{3}{8}$
c. $\frac{1}{8}$
d. $\frac{1}{8}$