Question

When the phenotypes controlled by two alleles are equally displayed in the heterozygote, the two alleles are said to show a. codominance. b. complete dominance. c. incomplete dominance. d. epistasis.

Short answer

a. codominance

Step-by-step solution

Understand the Definitions

First, identify and understand the definitions of the key terms: codominance, complete dominance, incomplete dominance, and epistasis. Codominance: Both alleles in a heterozygote are fully expressed, leading to a phenotype that shows both traits. Complete Dominance: One allele completely masks the effect of the other in a heterozygote. Incomplete Dominance: The phenotype of a heterozygote is an intermediate blend of the parental traits. Epistasis: One gene's allele affects or masks the expression of another gene's allele.

Analyze the Question

Look at the question again: When the phenotypes controlled by two alleles are equally displayed in the heterozygote, which pattern of inheritance is it describing? The key part here is 'equally displayed in the heterozygote'.

Match the Definition

Based on the definitions from Step 1, match the phrase 'equally displayed in the heterozygote' to the correct term. Codominance fits the description because both alleles are fully and equally expressed in the phenotype of the heterozygote.

Choose the Correct Answer

From the given options: a. Codominance b. Complete Dominance c. Incomplete Dominance d. EpistasisThe correct answer is 'a. codominance'.

Key concepts

genetic inheritance

Genetic inheritance refers to how characteristics or traits are passed from parents to offspring through genes. Genes are made up of DNA and exist in pairs called alleles. These alleles can be either dominant or recessive.
The combination of these alleles determines the observable traits, or phenotypes, of an organism.
When we discuss genetic inheritance, we're looking at:

• Dominant alleles, which mask the effects of recessive alleles in heterozygotes.
• Recessive alleles, which only show their traits when paired with another recessive allele.
• Codominance, where both alleles in a pair are fully expressed.
• Incomplete dominance, where the heterozygote shows a blend of the two traits.
• Epistasis, where one gene's expression can affect or mask another gene's expression.

Understanding these basic principles helps us figure out how traits like eye color, blood type, and even certain diseases are inherited.

alleles

Alleles are different versions of the same gene. Each individual has two alleles for each gene—one inherited from each parent. These alleles can be identical (homozygous) or different (heterozygous).
The way these alleles interact determines the organism's phenotype.
For example:

• In **complete dominance**, a dominant allele will completely mask the presence of a recessive allele.
• In **incomplete dominance**, neither allele is completely dominant, and the resulting phenotype is a blend.
• In **codominance**, both alleles are equally expressed, leading to a phenotype that shows both traits separately.

Epistasis involves interactions between different genes, which can complicate how alleles express themselves.
Knowing how alleles work together helps us understand more about genetics and inheritance patterns.

phenotype expression

Phenotype expression refers to the observable characteristics of an organism that result from the interaction of its genotype (the genetic makeup) with the environment.
This interaction determines traits like skin color, height, and even certain behaviors.
Phenotype expression is influenced by:

• The types of alleles an organism has.
• The dominance relationships between these alleles (complete dominance, incomplete dominance, codominance).
• Environmental factors that can affect gene expression.

For instance: In codominance, both alleles contribute equally and independently to the phenotype. In a flower with codominant red and white alleles, both colors might be present as distinct patches.
Recognizing how these diverse influences converge in phenotype expression allows us to predict certain traits and understand more about genetic diversity within populations.