Problem 11 - Biology Concepts and Applications

Question

The phenotype of individuals heterozygous for _____ alleles comprises both homozygous phenotypes. a. epistatic c. pleiotropic b. codominant d. hybrid

Step-by-Step Solution

Answer

Codominant alleles.

Step 1: Understanding the Question

The question is asking which type of alleles result in a mixture of both homozygous phenotypes when an individual is heterozygous for those alleles. We need to identify the correct scientific term that describes this genetic expression.

Step 2: Review Genetic Terms

- **Epistatic** alleles interact such that one allele masks the effect of another allele at a different locus. - **Pleiotropic** alleles affect multiple traits from a single gene. - **Codominant** alleles result in both alleles being fully expressed in the phenotype. - **Hybrid** typically refers to offspring of two different species or varieties but is not used to describe gene interactions.

Step 3: Identify the Correct Term

The question refers to a situation where both alleles are expressed in the phenotype, which is characteristic of **codominant** alleles. In codominance, both alleles contribute equally and separately to the phenotype, displaying traits of both alleles.

Step 4: Conclude the Answer

Based on the descriptions, the term that fits the situation described in the question is 'codominant'. Therefore, for heterozygous individuals, both homozygous phenotypes are expressed when the alleles are codominant.

Key Concepts

Genetic Inheritance

Genetic inheritance is the process by which our traits are passed down from one generation to the next. It involves the transmission of genetic information from parents to offspring through genes, which are found on chromosomes. This is a fundamental principle of biology and helps explain why children often look similar to their parents.

• Each parent contributes half of the offspring's genetic material, thereby creating a unique combination of traits.
• These traits are determined by specific genes, which can exist in different forms known as alleles.

Genetic inheritance is governed by the rules established by Gregor Mendel in the 19th century, famously known as Mendel's laws of inheritance.
Mendel identified the principles of dominance, segregation, and independent assortment, providing the foundational framework for understanding heredity.

Alleles

Alleles are different versions of a gene that determine specific traits. Think of alleles as the alternative forms of one gene that occupy the same position on each pair of chromosomes.

• Each individual inherits two alleles for each gene, one from their mother and another from their father.
• These can be the same (homozygous) or different (heterozygous).

When discussing codominance, both alleles in a heterozygote are fully expressed, rather than one being dominant over the other. This results in a phenotype that clearly exhibits traits from both alleles.

For instance, in some animals, the alleles for coat color are codominant. A heterozygous individual might show patches of one color alongside patches of another, directly displaying both alleles at once.

Phenotype

Phenotype is the observable expression of an individual's genetic makeup. It encompasses physical and biochemical characteristics such as height, eye color, and blood type. Essentially, phenotype is how our genes manifest in real life.

• The phenotype is influenced not only by one's genes but also by environmental factors and interactions between genes.
• In cases of codominance, the phenotype includes characteristics of both alleles, making it a complete expression of both genetic contributions.

An example is human blood type, where both A and B alleles are codominant. Therefore, someone with both alleles shows an AB blood type, demonstrating both the A and B traits equally.