Question

In the rat, the allele for red eye colour is dominant over the alleles for brown colour. Consider a cross between a rat that is an Hozygote dominant for eye colour and a rat that is an Hozygote recessive for eye colour.
1. Show the parental genetic cross between the two rats.
2. Use a Punnett square to show the F1 (filial generation).
3. Indicate the genotype and phenotype of the F1 generation.
4. With the results of the F1 generation, construct a Punnett square showing the results of an F2 (generation).
5. Indicate the genotype and phenotype of the F2 generation

Answer 1

Answer:

1) RR x rr

2) Shown below

3) 100% Rr with red eyes

4) Punnett square shown (Rr x Rr)

5) 25% of the offspring are h0m0zygous dominant with red eyes (RR), 50% are heterozygous with red eyes (Rr), and 25% are h0m0zygous with brown eyes (rr)

Explanation:

Let's say the allele for red eyes is R and the allele for brown eyes is r.

1. A cross between a h0m0zygous dominant (two copies of the dominant allele, R) and h0m0zygous recessive (two copies of the recessive allele, r) is: RR x rr

2.                            R                  R

                  r          Rr                Rr

                 

                  r          Rr                Rr

The F1 generation is shown in the Punnett square above.

3. The F1 generation are 100% Rr. They are heterozygous. Since red (R)                     is dominant, the rats all have red eyes

4. A cross between the F1 generation (Rr x Rr) gives the F2 generation

                              R                  r

                  R         RR              Rr

                 

                  r          Rr                rr

5. 25% of the offspring are h0m0zygous dominant with red eyes (RR), 50% are heterozygous with red eyes (Rr), and 25% are h0m0zygous with brown eyes (rr)