Dominant

Definition

In genetics, the term dominant refers to an allele that expresses its trait even when paired with a recessive allele. This characteristic means that when an organism carries one dominant allele and one recessive allele for a specific gene, the dominant trait will be the one observed in the phenotype. Dominant alleles can mask the presence of recessive alleles, leading to variations in inherited traits and characteristics.

5 Must Know Facts For Your Next Test

1. Dominant alleles are often represented by uppercase letters, while recessive alleles are represented by lowercase letters.
2. When a dominant allele is present in an organism's genotype, the corresponding dominant trait will always be expressed in the phenotype.
3. In a heterozygous individual, only one copy of the dominant allele is needed to produce the dominant phenotype.
4. Dominance does not imply that the dominant allele is more common in the population; it simply refers to the expression of traits.
5. In cases of incomplete dominance or co-dominance, the interaction between dominant and recessive alleles can result in unique phenotypic expressions.

Review Questions

• How does the presence of a dominant allele affect phenotypic expression in an organism?
  • The presence of a dominant allele ensures that its corresponding trait is expressed in the organism's phenotype, even if paired with a recessive allele. This means that if an organism has at least one dominant allele for a specific gene, the trait associated with that allele will be visible. For example, if 'A' is a dominant allele and 'a' is recessive, an organism with genotypes 'AA' or 'Aa' will exhibit the 'A' trait.
• Compare and contrast homozygous and heterozygous genotypes in relation to dominant alleles.
  • Homozygous genotypes consist of two identical alleles, which can be either both dominant or both recessive. In contrast, heterozygous genotypes contain one dominant and one recessive allele. In terms of phenotypic expression, individuals with a homozygous dominant genotype will express the dominant trait fully, while heterozygous individuals will also express this trait due to the presence of at least one dominant allele. Therefore, both types will display the dominant phenotype, but only homozygous individuals carry two copies of that dominant allele.
• Evaluate the implications of dominance on genetic variation within populations and how it influences evolutionary processes.
  • Dominance plays a crucial role in genetic variation within populations by determining which traits are expressed and passed on to future generations. When dominant alleles prevail, they can overshadow recessive traits, potentially reducing genetic diversity. However, the interplay between dominant and recessive alleles contributes to evolutionary processes by enabling natural selection to favor certain traits over others. Over time, this can lead to shifts in allele frequencies within a population, influencing its adaptability and resilience to environmental changes.

Related terms

Recessive:

An allele that only expresses its trait when two copies are present; it is masked by dominant alleles.

Homozygous: A genetic condition where an individual has two identical alleles for a particular trait, either both dominant or both recessive.

Heterozygous: A genetic condition where an individual has two different alleles for a particular trait, one dominant and one recessive.