Question

When both a dominant and recessive allele for a particular gene are present together in the same plant, what happens?

1) the recessive allele is always expressed
2) both the dominant and recessive alleles are expressed
3) the dominant allele is always expressed
4) the dominant allele is masked by the recessive allele
5) a and d

Answer 1

When a plant has both a dominant and recessive allele for a gene, the dominant allele is always expressed, masking the recessive allele.

Step-by-step explanation:

When both a dominant and recessive allele for a particular gene are present together in the same plant, the dominant allele is always expressed. This is a fundamental concept in genetics known as Mendel's law of dominance. It states that the presence of a dominant allele will mask the expression of a recessive allele in a heterozygote; therefore, the plant will exhibit the characteristic associated with the dominant allele.

Using the example of Mendel's pea plants, a plant with a heterozygous genotype for height (Tt), with 'T' being the dominant tall allele and 't' the recessive dwarf allele, will be tall. This is because the dominant 'T' allele will mask the expression of the recessive 't' allele. Therefore, option 3) the dominant allele is always expressed, is the correct answer to the student's question.