Question

4. In shorthorn cattle, when a red bull (RR) is crossed with a white cow (R'R'), all the offspring are roan a spotted red and white (milky red) color.

What are the genotypic and phenotypic ratios of the F1 cross (RR x WW)

What are the genotypes and phenotypic ratios of the F2 cross (Cross 2 F1 offspring)

Answer 1

In Shorthorn cattle, the alleles for color are represented as follows:
- **R:** Red allele
- **R' (or W):** White allele

When a red bull (genotype RR) is crossed with a white cow (genotype R' R'), all the resulting offspring (F1 generation) will be roan (phenotype) with the genotype R R'.

### F1 Cross (RR x R'R')

**Genotypic Ratio:**
- All offspring have the genotype R R' (1:0 for RR and R'R').

**Phenotypic Ratio:**
- All offspring exhibit the roan phenotype (milky red) (1:0 for roan and any other phenotype).

#### Summary for F1 Generation:
- Genotypic Ratio: 1 (R R')
- Phenotypic Ratio: 1 (roan)

### F2 Cross (Crossing F1 Offspring, R R' x R R')

To find the genotypic and phenotypic ratios of the F2 generation, we need to cross two F1 individuals (both R R').

When we set up a Punnett square for the cross R R' x R R':

| | R | R' |
|------|--------|--------|
| R | RR | R R' |
| R' | R R' | R'R' |

**Genotypes from the F2 cross:**
1. RR (homozygous red)
2. R R' (heterozygous which is roan)
3. R'R' (homozygous white)

### Genotypic Ratio of F2:
- 1 RR : 2 R R' : 1 R'R'

### Phenotypic Ratio of F2:
- The phenotypes will be:
- Red (RR): 1
- Roan (R R'): 2
- White (R'R'): 1

Thus, the phenotypic ratio is:
- 1 Red : 2 Roan : 1 White

#### Summary for F2 Generation:
- Genotypic Ratio: 1 RR : 2 R R' : 1 R'R'
- Phenotypic Ratio: 1 Red : 2 Roan : 1 White