Question

Red hair is dominant over yellow hair in some cattle. Which of the following shows a 50% probability that cattle offspring will have red hair? A. rr, rr, rr, rr. B. Rr, rr, Rr, rr. C. RR, Rr, RR, Rr. D. RR, RR, RR, RR

Answer 1

To determine which option shows a 50% probability that cattle offspring will have red hair, let's first define the alleles involved:

- **R** = red hair (dominant)
- **r** = yellow hair (recessive)

In the offspring, red hair will be expressed when at least one **R** allele is present.

Now, let's analyze each option:

A. **rr, rr, rr, rr.**
- All offspring are **rr** (yellow hair). No **R** alleles present.
- Probability of red hair = 0%.

B. **Rr, rr, Rr, rr.**
- Offspring genotypes: 2 are **Rr** (red hair) and 2 are **rr** (yellow hair).
- Probability of red hair = 50% (2 out of 4).

C. **RR, Rr, RR, Rr.**
- Offspring genotypes: 2 are **RR** (red hair) and 2 are **Rr** (red hair).
- Probability of red hair = 100% (all are red hair).

D. **RR, RR, RR, RR.**
- All offspring are **RR** (red hair). No **r** alleles present.
- Probability of red hair = 100% (all are red hair).

The only option with a 50% probability of the offspring having red hair is:

**B. Rr, rr, Rr, rr.**