A pea plant is heterozygous for seed colour and homozygous for seed shape. Yellow seed colour (Y) is dominant to green seed colour (y). Round seed shape (R) is dominant to wrinkled seed shape (r).
Using the information provided, which of the following statements, taken independently, could be correct?
1 This plant contains the alleles Y, y, R and r.
2 This plant contains only the alleles Y, y and R.
3 This plant contains only the alleles Y, R and r.
4 The genotype of this plant for seed colour is Yy.
5 The genotype of this plant for seed colour is YY.
6 The genotype of this plant for seed shape is Rr.
7 The genotype of this plant for seed shape is rr.

Answer:

17) D

We know the pea plant is heterozygous for seed colour. The alleles for seed colour are Y and y. Therefore, the pea plant definitely has alleles Y and y.

We are only told that the pea plant is homozygous for seed shape. We are not given any information about whether it is homozygous dominant or homozygous recessive. It can either be ‘RR’ or ‘rr’ and NOT ‘Rr’

Statement 1 is wrong because the pea plant cannot have both ‘R’ and ‘r’.
Statement 2 could be correct. We know it has alleles ‘Y’ and ‘y’. It could also have ‘R’.

Statement 3 could not be correct. It cannot contain both alleles for seed shape ‘R’ and ‘r’.

Statement 4 is correct. We know it is heterozygous for seed colour, so it’s genotype for seed colour has to be ‘Yy’.

Statement 5 cannot be correct. The genotype for seed colour has to be ‘Yy’ and not ‘YY’.

Statement 6 cannot be correct. The plant is homozygous for seed shape. So it cannot be ‘Rr’.

Statement 7 could be correct. Its genotype for seed shape could be ‘rr’.

So D is correct.