Question

In garden pea plants, the allele for inflated pod (i) is dominant to the allele for constricted pod (i). A cross between ii and ii produces:

Options:
Option 1: all constricted pods
Option 2: all inflated pods
Option 3: 3/4 inflated pods and 1/4 constricted pods
Option 4: 1/2 inflated pods and 1/2 constricted pods

Answer 1

A cross between two homozygous recessive (ii) pea plants for pod shape results in all offspring with constricted pods. In a dihybrid cross of heterozygous tall/inflated (TtIi) pea plants, 650 inflated-pod plants in the F2 generation would suggest approximately 217 constricted-pod plants, according to a 3:1 phenotypic ratio.

Step-by-step explanation:

In the scenario described, where a cross between two homozygous recessive (ii) pea plants for pod shape is being considered, the correct answer is that such a cross would produce all constricted pods. This is because both parents can only pass on the i allele, and since there are no dominant alleles present, all offspring will have the genotype ii, expressing the recessive constricted pod trait.

Now, considering a dihybrid cross between heterozygous tall/inflated (TtIi) pea plants, based on Mendelian genetics, we would expect offspring to exhibit a phenotypic ratio of 9 tall/inflated : 3 tall/constricted : 3 dwarf/inflated : 1 dwarf/constricted. As inflated pods are dominant (I), if there are 650 inflated-pod plants, we would expect approximately 1/3 of that number to have constricted pods, since the phenotypic ratio for pod shape in the F2 generation is 3 inflated to 1 constricted. Hence, the number of constricted-pod plants can be calculated as 650 / 3, which is approximately 217 constricted-pod plants.

The crosses should be carefully controlled to prevent self-fertilization, ensuring the traits are inherited according to Mendelian principles of genetics. In this case, TtIi x TtIi cross illustrates independent assortment as depicted by the figure showing the 16 possible offspring genotypes.