Using a Punnett Square, workout the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
Let us consider a cross between a homozygous recessive female (vv) and a heterozygous male (Vv) for a single locus, where V (violet flower) is dominant over v (white flower).
The homozygous female (vv) produces gametes carrying only the recessive allele 'v'. The heterozygous male (Vv) produces two types of gametes in equal proportion - 50% carrying 'V' and 50% carrying 'v'.
Using the Punnett Square:
| V | v | |
|---|---|---|
| v | Vv | vv |
| v | Vv | vv |
The F₁ generation shows a phenotypic ratio of 1:1 - 50% offspring with dominant phenotype (violet flowers, Vv) and 50% with recessive phenotype (white flowers, vv).
Explanation
This question tests the student's understanding of Punnett Square application. The context describes Punnett Square as 'a graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross.' When crossing homozygous recessive (vv) with heterozygous (Vv), the result is a 1:1 phenotypic ratio, which the context connects to test cross analysis.
Solution Steps
Step 1: Identify parental genotypes - Homozygous female (vv) × Heterozygous male (Vv)
Step 2: Determine gametes - Female produces 'v' only; Male produces 'V' and 'v' in equal proportion
Step 3: Construct Punnett Square with female gametes on one axis and male gametes on the other
Step 4: Fill in all possible combinations - Vv and vv each appearing twice
Step 5: Calculate phenotypic ratio - 1 dominant (Vv) : 1 recessive (vv)