4. In roses, long stem is dominant over short stems. A Homozygous long-stemmed plant is crossed
with a homozygous short-stemmed plant. What percentage of the resultant rose plants will have long stems?

100%

Explanation:

This question involves a single gene coding for stem length in the rose plant. The allele for long stem (L) is dominant over the allele for short stem (l). This means that allele L will mask the phenotypic expression of allele l in a heterozygous state.

According to the question, a homozygous long-stemmed rose i.e. a rose plant that has same alleles for long stem, LL and a homozygous short-stemmed plant i.e. a rose plant that has same alleles for short stem, ll is crossed. Using a punnet square, all the F1 offsprings of this cross will have a genotype: Ll

Since (L) is dominant over (l), offsprings (Ll) will have a long-stemmed phenotype. Since all offsprings are long-stemmed, this means that 100% of the offsprings are long-stemmed.