Dominant

Definition

In genetics, the term dominant refers to an allele that expresses its trait or phenotype even when only one copy is present in the organism. This means that if an individual carries at least one dominant allele, the characteristic associated with that allele will be observed, regardless of the presence of a recessive allele. Dominance can affect how traits are passed down through generations and can influence genetic variation within populations.

5 Must Know Facts For Your Next Test

1. Dominant alleles are represented by uppercase letters (e.g., 'A'), while recessive alleles are usually represented by lowercase letters (e.g., 'a').
2. In a heterozygous individual (one dominant and one recessive allele), the phenotype will reflect the dominant trait.
3. Dominance does not imply that the dominant allele is better or more common; it simply indicates how traits are expressed.
4. Some traits can exhibit incomplete dominance or codominance, where neither allele is completely dominant over the other.
5. Punnett squares are often used to predict the inheritance patterns of dominant and recessive alleles in offspring.

Review Questions

• How does the concept of dominance influence the expression of traits in heterozygous individuals?
  • Dominance influences trait expression in heterozygous individuals because the presence of one dominant allele is enough for the dominant phenotype to be expressed. For example, if an individual has one dominant allele (A) and one recessive allele (a), they will display the trait associated with allele A. This characteristic shows how certain traits can mask others when different alleles are present together.
• Discuss how understanding dominance can help predict inheritance patterns in genetic crosses.
  • Understanding dominance allows for more accurate predictions of inheritance patterns in genetic crosses. By using tools like Punnett squares, one can determine the likelihood of offspring inheriting certain traits based on the parental genotypes. For instance, knowing which alleles are dominant helps predict whether a trait will be visible in the offspring and how it may combine with other traits through generations.
• Evaluate the implications of dominant and recessive inheritance on genetic counseling and disease prediction.
  • The implications of dominant and recessive inheritance are significant in genetic counseling and disease prediction. Understanding whether a condition is caused by a dominant or recessive allele allows genetic counselors to provide informed risk assessments to families considering having children. For instance, if a disease is linked to a dominant allele, there is a 50% chance that an affected parent will pass it to their child. This knowledge helps families make informed decisions about their health and reproductive options.

Related terms

Allele: A variant form of a gene that can exist at a specific locus on a chromosome, which may result in different traits.

Recessive:

An allele that only expresses its trait when two copies are present, as it is masked by the presence of a dominant allele.

Homozygous: A genetic condition where an individual has two identical alleles for a specific gene, which can be either dominant or recessive.