Codominance and Incomplete Dominance Practice Worksheet

Understanding Codominance and Incomplete Dominance

In genetics, the relationship between alleles can be described as dominant, recessive, codominant, or incompletely dominant. While dominant and recessive relationships are relatively straightforward, codominance and incomplete dominance require a closer look. In this article, we will delve into the concepts of codominance and incomplete dominance, and provide a practice worksheet to help reinforce understanding.

Codominance

Codominance occurs when two different alleles have an equal effect on the phenotype of an individual. This means that neither allele is dominant or recessive, and both alleles are expressed equally. A classic example of codominance is the ABO blood type system in humans.

In the ABO blood type system, the A and B alleles are codominant, while the O allele is recessive. Individuals with the genotype AA or AO have type A blood, those with the genotype BB or BO have type B blood, and those with the genotype AB have type AB blood. In the case of the AB genotype, both the A and B alleles are expressed equally, resulting in the production of both A and B antigens on the surface of red blood cells.

Incomplete Dominance

Incomplete dominance occurs when one allele has a greater effect on the phenotype than the other allele, but not complete dominance. This means that the dominant allele does not completely mask the effect of the recessive allele. A classic example of incomplete dominance is the relationship between the red and white flower alleles in snapdragons.

In snapdragons, the red flower allele (R) is incompletely dominant over the white flower allele (r). Individuals with the genotype RR or Rr have pink flowers, while those with the genotype rr have white flowers. The red flower allele does not completely mask the effect of the white flower allele, resulting in the production of pink flowers in individuals with the Rr genotype.

Practice Worksheet

Now that we have covered the concepts of codominance and incomplete dominance, let's practice with some exercises.

Exercise 1: What is the genotype and phenotype of an individual with type AB blood?

Genotype: _______________________ Phenotype: _______________________

Exercise 2: A cross is made between two snapdragon plants, one with red flowers (RR) and the other with white flowers (rr). What is the genotype and phenotype of the offspring?

Genotype: _______________________ Phenotype: _______________________

Exercise 3: A couple has a child with type A blood. What are the possible genotypes of the parents?

Parent 1: _______________________ Parent 2: _______________________

Exercise 4: A plant with pink flowers (Rr) is crossed with a plant with white flowers (rr). What is the genotype and phenotype of the offspring?

Genotype: _______________________ Phenotype: _______________________

Answers

Exercise 1: Genotype: AB, Phenotype: Type AB blood

Exercise 2: Genotype: Rr, Phenotype: Pink flowers

Exercise 3: Parent 1: AA or AO, Parent 2: AA or AO

Exercise 4: Genotype: Rr or rr, Phenotype: Pink flowers or white flowers

📝 Note: The answers to the exercises are based on the assumption that the alleles are codominant or incompletely dominant, as described in the examples.

In conclusion, understanding codominance and incomplete dominance is essential for predicting the outcomes of genetic crosses and understanding the relationship between genotype and phenotype. By practicing with exercises like the ones provided above, you can reinforce your understanding of these concepts and become more proficient in genetics.