Complete dominance

Definition

Complete dominance is a genetic scenario where one allele completely masks the expression of another allele for a specific trait, resulting in a phenotype that is solely reflective of the dominant allele. This phenomenon ensures that the dominant trait is expressed in the phenotype of heterozygous individuals, overshadowing the recessive trait. Understanding complete dominance is crucial in predicting offspring traits and analyzing genetic crosses, which involve gene interactions and probabilities.

5 Must Know Facts For Your Next Test

1. In complete dominance, only the dominant allele's trait will appear in the phenotype when at least one dominant allele is present in the genotype.
2. A classic example of complete dominance can be seen in Mendelian traits like pea plant flower color, where purple is dominant over white.
3. Heterozygous individuals will display the same phenotype as homozygous dominant individuals due to the complete masking of the recessive allele.
4. Complete dominance can significantly impact inheritance patterns and ratios seen in offspring during genetic crosses.
5. This concept is foundational in genetics and helps simplify the understanding of more complex inheritance patterns involving multiple alleles or interactions.

Review Questions

• How does complete dominance affect the phenotypic ratios observed in offspring from a monohybrid cross?
  • In a monohybrid cross involving complete dominance, offspring typically display a phenotypic ratio of 3:1 for dominant to recessive traits when two heterozygous parents are crossed. This occurs because the dominant allele masks the effect of the recessive allele in heterozygous individuals, leading to three showing the dominant trait and one displaying the recessive trait. This ratio illustrates how complete dominance shapes observable traits in subsequent generations.
• Discuss how understanding complete dominance can influence predictions made using Punnett squares in genetic crosses.
  • Understanding complete dominance allows for accurate predictions when using Punnett squares by clarifying which alleles will be expressed in offspring. When constructing a Punnett square, knowing that only the dominant allele will influence phenotype simplifies calculations. For instance, when crossing two heterozygous plants, the resulting square reveals three offspring with the dominant trait for every one with the recessive trait, showcasing the effects of complete dominance on inheritance patterns.
• Evaluate the implications of complete dominance in the context of three-point crosses and gene order determination.
  • Complete dominance plays a crucial role in interpreting results from three-point crosses as it helps clarify how different alleles contribute to observable traits. When analyzing gene order and recombination frequencies, understanding which traits exhibit complete dominance allows researchers to discern patterns in inheritance more effectively. This knowledge can lead to more accurate mapping of genes on chromosomes, as knowing whether an allele is dominant can influence interpretations of gene linkage and distances based on phenotypic outcomes.

Related terms

Dominant Allele: An allele that expresses its phenotype even in the presence of a recessive allele, overpowering its effect.

Recessive Allele: An allele that only expresses its phenotype when paired with another recessive allele; it is masked by a dominant allele.

Punnett Square: A diagram used to predict the genetic outcome of a cross between two individuals, illustrating how alleles combine in offspring.