Biology benchmark 2 semester exam fall 24

Question

A student is investigating patterns in inheritance by crossing 2P plants.She creates the puninett square shown below
Which explanation of the inheritance of shape in peplants is supported by the punnett square
The alleles for shape show a pattern of codominace
The alleles for shape show a pattern of incomplete dominance
The allele for round shape (R) is dominant to the allele for wrinkled shape (r)
The allele for wrinkled shape (r) is dominant to the allele for round shape (R)

Answer 1

To determine which explanation of the inheritance of shape in pea plants is supported by the Punnett square, we need to consider the different patterns of inheritance and what the Punnett square typically displays.

1. Codominance: This occurs when both alleles in a heterozygote are fully expressed, leading to a phenotype that shows both traits simultaneously. For example, if R (round) and r (wrinkled) are co-dominant, the phenotype for Rr would display both round and wrinkled characteristics.

2. Incomplete Dominance: This occurs when the heterozygous phenotype is a blend of the two alleles. For example, if R (round) and r (wrinkled) exhibit incomplete dominance, a homozygous round (RR) would produce a round phenotype, while the homozygous wrinkled (rr) would produce a wrinkled phenotype, and Rr could give rise to an intermediate phenotype (a blend).

3. Dominance Relationships: Here, we usually note that one allele completely masks the effect of the other. If R is dominant over r, then Rr (heterozygous) would appear round, while only rr would be wrinkled. Conversely, if r is dominant, then only rr would be wrinkled, while any presence of R (RR or Rr) would lead to a round appearance.

Since we lack the specific Punnett square results, we can talk through these options in general terms:

• If the Punnett square shows a phenotypic ratio of 3:1 for round to wrinkled, it suggests that round (R) is dominant over wrinkled (r).
• If the ratio were 1:2:1, where one phenotype is distinctly intermediate, it would suggest incomplete dominance.
• To support codominance, we would expect to see cases where both traits are expressed equally in the phenotype (for example, speckled or a combination of both shapes).

Without the actual results plotted in the Punnett square, the most common scenario for pea plant shape inheritance—which relies on the classical Mendelian dominance—is that the allele for round shape (R) is dominant to the allele for wrinkled shape (r).

Thus, the correct answer based on typical pea plant genetics would likely be:

The allele for round shape (R) is dominant to the allele for wrinkled shape (r).