Let's analyze the four statements based on the given genotypes and Punnett squares:
### Plants with short stems are homozygous for that trait.
- For a plant to have short stems, it must possess two recessive alleles (tt).
- 'tt' is a homozygous genotype because both alleles are the same (both recessive).
- Therefore, this statement is true.
### Plants with tall stems are always homozygous for that trait.
- A tall stem can result from either 'TT' (homozygous dominant) or 'Tt' (heterozygous).
- Since tall stems can be heterozygous (Tt), it is not necessary for tall plants to always be homozygous (TT).
- Therefore, this statement is false.
### Both parent plants in the second generation are heterozygous.
- The second-generation Punnett square indicates genotypes TT, Tt, Tt, and tt.
- For this Punnett square to occur, one parent must be 'Tt' and the other 'Tt', but the combinations shown indicate one parent is 'TT' and the other is 'tt'.
- This means the parents from the second generation are not both heterozygous.
- Therefore, this statement is false.
### Both parent plants in the second generation are homozygous.
- According to the Punnett square for the second generation (TT, Tt, Tt, tt), we deduce that the parents are 'TT' (homozygous dominant) and 'tt' (homozygous recessive).
- Both parents are indeed homozygous, just for different traits.
- Therefore, this statement is true.
### Conclusion
Based on the analysis:
- Plants with short stems are homozygous for that trait.
- Both parent plants in second generation are homozygous.
So, the correct statements are:
- Plants with short stems are homozygous for that trait.
- Both parent plants in second generation are homozygous.
