Dominant

Definition

In genetics, the term 'dominant' refers to an allele that expresses its phenotype even when only one copy is present in a heterozygous individual. This characteristic means that dominant alleles can mask the effects of recessive alleles, resulting in traits that are observable in the organism. Dominance is a fundamental concept in understanding how traits are inherited and can influence genetic linkage and recombination during crossing over.

5 Must Know Facts For Your Next Test

1. Dominant alleles are represented with uppercase letters (e.g., 'A') while recessive alleles are represented with lowercase letters (e.g., 'a').
2. In a dihybrid cross, the presence of dominant alleles can influence the segregation patterns of linked genes during meiosis.
3. The concept of dominance is critical for predicting phenotypic ratios in offspring from parental genotypes, particularly in Mendelian inheritance.
4. Dominance can sometimes be incomplete or co-dominant, leading to varying expressions of traits depending on the combination of alleles present.
5. Understanding dominance is essential for interpreting genetic mapping and identifying gene interactions that can occur during crossing over.

Review Questions

• How do dominant alleles influence the expression of traits in heterozygous individuals?
  • Dominant alleles have the ability to mask the expression of recessive alleles in heterozygous individuals, meaning that only one copy of the dominant allele is needed for the associated phenotype to be expressed. This masking effect can lead to specific observable traits being passed on to offspring, allowing geneticists to predict inheritance patterns using Punnett squares and other tools. As a result, understanding dominance is key to studying how traits are inherited across generations.
• Discuss the role of dominant alleles in genetic linkage and crossing over during meiosis.
  • Dominant alleles play a significant role in genetic linkage because they can influence the inheritance of nearby genes on the same chromosome. During crossing over, when homologous chromosomes exchange segments, dominant alleles may stay together with linked genes due to their proximity. This linkage affects how traits are inherited as a unit, which can impact genetic variation within populations and the expression of certain phenotypes.
• Evaluate how the concept of dominance complicates our understanding of inheritance patterns, especially in cases of incomplete dominance and co-dominance.
  • The concept of dominance complicates inheritance patterns as it does not always apply uniformly across all genes. In cases of incomplete dominance, neither allele is completely dominant, resulting in a blend of phenotypes in heterozygotes. Co-dominance also presents challenges, where both alleles are expressed equally, leading to distinct phenotypic manifestations. These exceptions to simple dominance complicate predictions regarding inheritance and emphasize the need for more nuanced models to understand genetic interactions and expressions.

Related terms

Recessive: An allele that only expresses its phenotype when two copies are present in a homozygous individual, effectively being masked by dominant alleles.

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

Phenotype: The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.