Dominance

Definition

Dominance is a genetic concept where one allele masks the expression of another allele for a given trait in a heterozygous individual. This masking effect means that the dominant allele's phenotype will be expressed, while the recessive allele's phenotype remains hidden. Understanding dominance is essential for predicting inheritance patterns and phenotypic ratios in offspring based on parental genotypes.

5 Must Know Facts For Your Next Test

1. Dominance can be classified into different types, including complete dominance, incomplete dominance, and co-dominance, each describing how alleles interact.
2. In complete dominance, the phenotype of the heterozygote is indistinguishable from that of the homozygous dominant individual.
3. In incomplete dominance, the phenotype of the heterozygote is an intermediate blend between the two homozygous phenotypes.
4. Co-dominance occurs when both alleles in a heterozygote are fully expressed, resulting in offspring with distinct traits from both parents.
5. The principles of dominance play a crucial role in Mendelian genetics and are foundational for understanding more complex patterns of inheritance.

Review Questions

• How does dominance influence the phenotypic expression of traits in heterozygous individuals?
  • Dominance influences phenotypic expression by determining which allele will be visible in an organism with two different alleles for a trait. In heterozygous individuals, the dominant allele masks the effect of the recessive allele, leading to the expression of only the dominant trait. This means that when examining offspring, one can predict phenotypic ratios based on which alleles are inherited from each parent.
• Compare and contrast complete dominance, incomplete dominance, and co-dominance in terms of their impact on phenotypic ratios in offspring.
  • Complete dominance results in offspring that exhibit the dominant phenotype whenever at least one dominant allele is present, leading to phenotypic ratios such as 3:1 in a monohybrid cross. Incomplete dominance creates an intermediate phenotype, resulting in a ratio of 1:2:1 among offspring showing the three phenotypes (two homozygous and one heterozygous). Co-dominance results in both alleles being expressed distinctly, producing offspring with a mixture of traits from both parents without blending, which can also create unique phenotypes depending on how those alleles interact.
• Evaluate how understanding dominance is essential for predicting genetic outcomes in breeding experiments and its implications for agriculture and medicine.
  • Understanding dominance is crucial for predicting genetic outcomes as it allows breeders to anticipate which traits will be expressed in future generations based on parental genotypes. This knowledge enables more effective breeding strategies to enhance desirable traits in crops or livestock. In medicine, it can inform genetic counseling by helping individuals understand how certain inherited disorders may manifest based on dominant or recessive alleles. Ultimately, grasping the concept of dominance helps in making informed decisions that can impact agricultural yields and health outcomes.

Related terms

Allele: Different forms of a gene that can exist at a specific locus on a chromosome, which contribute to variations in traits.

Homozygous: An organism with two identical alleles for a specific gene, resulting in a consistent expression of that trait.

Phenotype: The observable characteristics or traits of an organism that result from the interaction of its genotype with the environment.