Question

A gene that affects three traits is _____. a. epistatic c. pleiotropic b. a multiple allele system d. dominant

Short answer

The gene is pleiotropic.

Step-by-step solution

Understand the Definitions

Let's begin by understanding the definitions of each option given in the question: a. Epistatic: This refers to a gene that can mask or suppress the expression of another gene. b. A multiple allele system: This refers to a situation where there are more than two alleles for a genetic locus within a population. c. Pleiotropic: This refers to a single gene that influences multiple phenotypic traits. d. Dominant: This refers to an allele that masks the expression of the other allele in a heterozygous individual.

Identify the Correct Term

The question asks for a term describing a gene that affects three traits. Considering the definitions checked in Step 1, a pleiotropic gene affects multiple phenotypic traits, fitting the description perfectly. Therefore, the correct term that refers to a gene affecting three traits is a pleiotropic gene.

Key concepts

Epistasis

In genetics, "epistasis" is an interesting concept where one gene's expression can interfere with or mask the effect of another gene. It is as if a gene can "turn off" another gene, causing a change in expression outcomes. This is different from dominance, where an allele can mask another allele within the same gene.

• Epistatic interactions often occur in genes that are part of the same biological pathway.
• Essentially, if Gene A is functioning properly, it may hide the effect of Gene B, unless a mutation or variation disrupts Gene A's expression.
• This concept helps explain complex traits and is crucial when studying how certain traits are inherited together.

The effect of epistasis can complicate genetic predictions, making it difficult to analyze traits just based on individual gene analysis. Understanding epistasis provides deeper insights into genetic complexities and can aid in fields like plant breeding and medical research.

Multiple Allele System

A "multiple allele system" involves more than two alleles for a genetic locus within a population. Unlike simple Mendelian genetics where each gene is represented by two alleles, multiple allele systems allow for greater genetic diversity.

• For example, the ABO blood type system is controlled by three alleles: I_A, I_B, and i.
• Each person can only have two of these alleles at a time, but the different combinations allow for blood types A, B, AB, or O.
• These systems play a significant role in genetic variation and adaptability in populations.

Multiple allele systems can deeply influence evolutionary processes by providing various possible phenotypes, giving species an adaptive advantage in changing environments.

Dominance in Genetics

"Dominance in genetics" refers to the relationship between alleles, where one allele can mask the expression of another allele within the same gene. When an individual has two different alleles of a gene (heterozygous), the dominant allele's trait is the one that gets expressed.

• Dominance does not mean one allele is better, more common, or more "powerful"; it's simply about which trait appears.
• Classic examples are found in Mendelian traits like eye color, where brown alleles can be dominant over blue.
• Co-dominance and incomplete dominance are variations where alleles may produce a blended phenotype or both traits expressed equally.

Understanding dominance helps predict traits passed from parents to offspring, especially in simple Mendelian inheritance. It forms a fundamental basis of classical genetics.