Question

Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?

1) All round seeds
2) All wrinkled seeds
3)¼ RR, ½ Rr,¼ rr
4) 3 round seeds, 1 wrinkled seed

Answer 1

In the F2 generation of a cross between an RR and rr pea plant, the frequency of phenotypes is 3 round seeds to 1 wrinkled seed, which is a standard Mendelian 3:1 ratio for a monohybrid cross involving a dominant and recessive allele.

Step-by-step explanation:

The student's question is about genetics and specifically Mendelian inheritance in pea plants. The dominant trait is round seed shape (R), and the recessive trait is wrinkled seed shape (r). When an RR plant (homozygous dominant) is crossed with an rr plant (homozygous recessive), the F1 generation will be all heterozygous (Rr) showing the dominant round seed phenotype. Now, when F1 plants self-pollinate or are crossed among each other, the F2 generation will exhibit a phenotypic ratio of 3 round seeds to 1 wrinkled seed, due to Mendel's principles of segregation and independent assortment.

To find the frequency of the phenotypes in the F2 generation, we use a Punnett square, displaying the possible genotypes of the offspring. The F1 generation (Rr) will produce gametes with R and r alleles in equal frequencies. When crossed, the offspring (F2 generation) genotypes will be 1 RR (round), 2 Rr (round), and 1 rr (wrinkled). Therefore, the phenotypic ratio is indeed 3 round to 1 wrinkled seed.