Question

1. smooth pod shape is dominant over constricted in pea plants. fill in the punnett square and determine the expected genotypic and phenotypic ratios from crossing homozygous recessive and homozygous dominant parents.

genotypes: ____________
genotypic ratio: ____________

Explanation:

Let's denote the dominant allele for smooth pod shape as \( S \) and the recessive allele for constricted pod shape as \( s \). The homozygous dominant parent will have the genotype \( SS \), and the homozygous recessive parent will have the genotype \( ss \).

Step 1: Determine the gametes

The homozygous dominant parent (\( SS \)) can only produce gametes with the \( S \) allele. The homozygous recessive parent (\( ss \)) can only produce gametes with the \( s \) allele.

Step 2: Fill in the Punnett square

	\( S \)	\( S \)
\( s \)	\( Ss \)	\( Ss \)

Step 3: Determine the genotypes

From the Punnett square, all the offspring have the genotype \( Ss \).

Step 4: Determine the genotypic ratio

Since all four offspring have the same genotype (\( Ss \)), the genotypic ratio is \( 4:0 \) for \( Ss:SS \) and \( Ss:ss \), but more accurately, since all are \( Ss \), the ratio of \( Ss \) to others is \( 4:0 \), or simply all \( Ss \), so the genotypic ratio is \( 1:0:0 \) (for \( SS:Ss:ss \)) but in terms of the possible genotypes here, since only \( Ss \) is present, the ratio is \( 4 \) \( Ss \) to \( 0 \) others, or simplified as \( 1 \) (for \( Ss \)) in a ratio context where we consider the types. But more precisely, when crossing \( SS \times ss \), the genotypic ratio of the offspring is \( 0:4:0 \) for \( SS:Ss:ss \), which can be simplified to \( 0:1:0 \) per type, but usually expressed as all heterozygous, so the genotypic ratio is \( 1 \) (for \( Ss \)) in the sense that all offspring are \( Ss \), so the ratio of \( Ss \) to non - \( Ss \) is \( 4:0 \), or when considering the three possible genotypes, \( SS:Ss:ss = 0:4:0=0:1:0 \) (dividing each by 4).

Answer:

Genotypes: All offspring have the genotype \( Ss \) (or writing the four genotypes as \( Ss, Ss, Ss, Ss \))
Genotypic Ratio: \( SS:Ss:ss = 0:4:0 \) (or simplified as \( 0:1:0 \) when considering the ratio per type, or \( 4:0 \) for \( Ss \) to non - \( Ss \) genotypes)