Question

Two pea plants produce the following offspring:225 tall with purple flowers250 short with white flowers237 tall with white flowers241 short with purple flowersWhich of the following parental pairs is more likely - two plants heterozygous for both genes, or one heterozygous for both genes and one homozygous recessive for both genes? Explain your answer.

Answer 1

Even without knowing which allele is dominant or recessive, we can understand the likely ancestors by analyzing the proportion among the offspring.

A crossing between two heterozygous will result in a 9/3/3/1 proportion (among 16 possible results), as follows:

- 9 will be dominant for both traits

- 3 will be dominant for the size and recessive for the color

- 3 will be recessive for the size and dominant for the color

- 1 will be recessive for both traits

But in a crossing between one heterozygous and one recessive, it will result in a 4/4/4/4 proportion (among 16 possible results), as follows:

- 4 will be dominant for both traits

- 4 will be dominant for the size and recessive for the color

- 4 will be recessive for the size and dominant for the color

- 4 will be recessive for both traits

Therefore, the option that fits better is the second option, as the result we see is closer to the 4/4/4/4 proportion. The correct answer is one heterozygous for both genes and one homozygous recessive for both genes.