In pea plants, flower color is determined by gene P (allele P for purple and allele p for red), while pollen shape is determined by gene L (allele L for long pollen and allele l for round pollen). A plant heterozygous for both the dominant purple allele (P) and the dominant long pollen allele (L) was crossed with a plant homozygous recessive for both traits. The phenotypic distribution among the offspring is as follows: 47 purple with long pollen, 47 red with round pollen, 3 purple with round pollen, and 3 red with long pollen. 1) Genes P and L assort independently. 2) Genes P and L are linked and located close together on the same chromosome. 3) Genes P and L are linked but located far apart on the same chromosome.

Question

In pea plants, flower color is determined by gene P (allele P for purple and allele p for red), while pollen shape is determined by gene L (allele L for long pollen and allele l for round pollen). A plant heterozygous for both the dominant purple allele (P) and the dominant long pollen allele (L) was crossed with a plant homozygous recessive for both traits. The phenotypic distribution among the offspring is as follows: 47 purple with long pollen, 47 red with round pollen, 3 purple with round pollen, and 3 red with long pollen. 1) Genes P and L assort independently. 2) Genes P and L are linked and located close together on the same chromosome. 3) Genes P and L are linked but located far apart on the same chromosome.

Biology · College · Mon Jan 18 2021

llm

Answered on Wed Nov 29 2023

The pattern observed for the offspring in this cross suggests that option 2, "genes P and L are linked and located close together on the same chromosome," is the correct interpretation.

In the scenario, the plant that is heterozygous for both traits (PpLl) is crossed with a plant that is homozygous recessive (ppll). Under independent assortment, we would expect to see a 1:1:1:1 phenotypic ratio because each gene assortment would occur independently during gamete formation, leading to four equally probable combinations of alleles.

However, the observed phenotypic distribution is:

- 47 purple with long pollen (P-L-) - 3 purple with round pollen (P-ll) - 3 red with long pollen (ppL-) - 47 red with round pollen (ppll)

These results indicate that the parental types (purple with long pollen and red with round pollen) are much more common than the recombinant types (purple with round pollen and red with long pollen), which is a strong indication of genetic linkage. Genetic linkage occurs when two genes are close together on the same chromosome and do not assort independently due to being physically connected. The small number of recombinant phenotypes suggests that while there was some crossing over between the P and L genes during gamete formation, it was not frequent, meaning they are likely located close to each other.

Thus, the most likely scenario is that genes P and L are linked and located close together on the same chromosome, leading to the observed non-Mendelian phenotypic distribution among the offspring.

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