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.

Question

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