Which best describes a recessive allele?
a)always inherited from a parent when a dominant allele is inherited from the other parent
b)never inherited from a parent when a dominant allele is inherited from the other parent
c)only determines phenotype when a dominant allele for the same trait is present
d)does not determine phenotype when a dominant allele for the same trait is present
The Correct Answer and Explanation is :
The best description of a recessive allele is:
d) does not determine phenotype when a dominant allele for the same trait is present.
Explanation
Alleles are different versions of a gene that contribute to an organism’s traits. In the context of genetics, alleles can be classified as dominant or recessive. A dominant allele is one that expresses its trait even when only one copy is present (heterozygous condition), whereas a recessive allele only expresses its trait when two copies are present (homozygous condition).
When an individual inherits two different alleles for a trait—one dominant and one recessive—the dominant allele will mask the expression of the recessive allele in the phenotype. For example, in pea plants, the allele for purple flowers (P) is dominant over the allele for white flowers (p). If a plant has one allele for purple flowers and one for white flowers (genotype Pp), the plant will display purple flowers, as the presence of the dominant allele P prevents the expression of the recessive allele p.
This characteristic of recessive alleles is essential for understanding Mendelian inheritance. For a recessive trait to manifest phenotypically, an individual must inherit two copies of the recessive allele—one from each parent. If an individual has only one dominant allele, the dominant phenotype will be expressed, and the recessive allele will remain unexpressed, influencing the phenotype only when two recessive alleles are present.
In summary, recessive alleles do not determine phenotype when a dominant allele is also present, as the dominant allele’s expression takes precedence. This principle underlies much of classical genetics and helps explain the inheritance patterns observed in various organisms.