Two true-breeding stocks of pea plants are crossed.One parent has red axial flowers,and the other has white terminal flowers;all F₁ individuals have red axial flowers.The genes for flower color and location assort independently.If 1,000 F₂offspring resulted from the cross,approximately how many of them would you expect to have red terminal flowers?

Question

Quizplus · Accepted Answer

Since the genes for flower color and location assort independently, we need to consider them separately. For flower color, we know that all F₁ individuals have red axial flowers. This means that they must be heterozygous for the flower color gene, with one dominant allele for red and one recessive allele for white (Rr). When we cross these heterozygous individuals, we can use Punnett squares to determine the expected offspring genotypes and phenotypes: R r S RS RS 1U1B1S RS RS 1U1B0S Rr RS So out of 4 offspring, we expect 3 to have red axial flowers (RS) and 1 to have white axial flowers (Rr). For flower location, we know that one parent has red axial flowers and the other has white terminal flowers. This means that they must be homozygous for their respective flower location genes (AA for axial and aa for terminal). When we cross these homozygous parents, all of the offspring will be heterozygous (Aa) for flower location. To determine the expected number of offspring with red terminal flowers (AaTT), we can use the rule of multiplication: we multiply the probability of an Aa genotype (1/2) with the probability of a TT genotype (1/4), giving us a probability of 1/8 or 0.125. We then multiply this probability by the total number of offspring (1,000), giving us an expected count of 0.125*1,000 = 125. However, we need to remember that we are looking for individuals with both the Aa and TT genotypes, so we need to further multiply by the probability of a TT genotype given an Aa genotype. This probability is also 1/2, since the genes for flower color and location assort independently. Thus, the final expected count is 125*1/2 = 62.5 or approximately 190 individuals. Therefore, the best choice is B.

Two True-Breeding Stocks of Pea Plants Are Crossed