When two heterozygous squash plants are crossed, each parent has the genotype Yy, where 'Y' represents the dominant allele for yellow fruit and 'y' represents the recessive allele for white fruit. Let's explore the possible genotypes of the offspring through this cross using a Punnett square:
1. Prepare the gametes: Each parent can contribute either a 'Y' allele or a 'y' allele.
- Parent 1 (Yy) can produce gametes: Y or y.
- Parent 2 (Yy) can produce gametes: Y or y.
2. Cross the gametes to see all possible combinations of the offspring:
```
Y y
----------------
Y | YY | Yy |
----------------
y | yY | yy |
----------------
```
3. Determine the genotypes:
- YY: The offspring receives a 'Y' allele from both parents.
- Yy: The offspring receives a 'Y' allele from Parent 1 and a 'y' allele from Parent 2.
- yY: The offspring receives a 'y' allele from Parent 1 and a 'Y' allele from Parent 2. Note that 'Yy' and 'yY' are functionally the same because 'Y' is dominant.
- yy: The offspring receives a 'y' allele from both parents.
4. Identify unique genotypes:
Considering “Yy” and “yY” are equivalent because the dominant allele 'Y' will mask the recessive allele 'y', the unique genotypes among the offspring are:
- YY
- Yy
- yy
Thus, the correct answer to the question regarding the possible genotypes of the offspring when two heterozygous yellow-fruit squash plants are crossed is:
- YY, Yy, yy only
