Dominant allele

Definition

A dominant allele is a variant of a gene that can mask or override the expression of another allele at the same locus. In Mendelian inheritance, when an organism has two different alleles for a particular trait, the dominant allele is the one that is expressed in the phenotype, while the recessive allele remains hidden unless two copies are present. This concept plays a crucial role in population genetics by influencing how traits are inherited and how they can spread through populations over generations.

5 Must Know Facts For Your Next Test

1. The presence of a dominant allele determines the phenotype in a heterozygous organism, meaning it will display the dominant trait.
2. In Mendelian genetics, dominant alleles are typically represented with uppercase letters, while recessive alleles are shown with lowercase letters.
3. If an individual inherits two different alleles for a trait, the dominant one will be expressed in their physical appearance.
4. Dominant alleles can lead to traits being passed on more frequently within a population, as they can mask the effects of recessive alleles.
5. In cases of incomplete dominance or codominance, the interaction between dominant and recessive alleles can create intermediate phenotypes or result in both traits being expressed.

Review Questions

• How does the presence of a dominant allele affect the phenotype of an organism?
  • The presence of a dominant allele determines the phenotype of an organism when it is heterozygous. This means that if an organism carries one dominant and one recessive allele for a specific trait, the dominant allele will mask the effect of the recessive allele, resulting in the organism displaying the trait associated with the dominant allele. In contrast, the recessive trait will only be observed if both alleles are recessive.
• Discuss the implications of dominant alleles in terms of genetic variation within a population.
  • Dominant alleles can significantly influence genetic variation within a population by allowing certain traits to become more common over generations. Because these alleles express their traits even when paired with recessive alleles, they can quickly establish themselves within a population. As organisms with advantageous dominant traits reproduce, these traits may spread more rapidly, impacting overall genetic diversity and potentially leading to changes in population dynamics.
• Evaluate the role of dominant and recessive alleles in understanding inheritance patterns and predicting genotypic ratios in offspring.
  • Dominant and recessive alleles play crucial roles in understanding inheritance patterns as they provide insight into how traits are passed from parents to offspring. By using tools like Punnett squares, one can predict genotypic ratios based on parental alleles. For instance, if both parents are heterozygous for a trait (one dominant and one recessive), the expected genotypic ratio among offspring would be 1:2:1 for homozygous dominant, heterozygous, and homozygous recessive respectively. Understanding these patterns helps scientists and geneticists assess probabilities of traits appearing in future generations.

Related terms

recessive allele: A recessive allele is a version of a gene that only expresses its trait when two copies are present, masking its effects when paired with a dominant allele.

homozygous: An organism is homozygous for a gene when it has two identical alleles, either both dominant or both recessive.

heterozygous: An organism is heterozygous for a gene when it has two different alleles, one dominant and one recessive.