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Chapter 5: Problem 4

If the phenotype trait of an \(A a\) heterozygous individual is the same as that of an \(A A\) homozygous individual, which allele is recessive?

Short Answer

Expert verified
Answer: The recessive allele is "a."

Step by step solution

01

Understanding Dominant and Recessive Alleles

Dominant alleles are those that always express their traits in the presence of another allele, which is recessive. Recessive alleles are those that require two copies, or both present alleles, to be the same for their traits to be expressed in an organism's phenotype.
02

Analyzing the Homozygous Individual Genotype

The homozygous individual in the given exercise has an \(AA\) genotype. When an individual is homozygous, it means that both of their alleles for a particular gene are the same. In this case, we focus on the phenotype of the \(AA\) genotype to draw a comparison with the heterozygous genotype.
03

Analyzing the Heterozygous Individual Genotype

The heterozygous individual in the given exercise has an \(Aa\) genotype. This means that the individual has two different alleles for the gene. Here we'll investigate whether the phenotype of the \(Aa\) genotype is the same as the \(AA\) genotype.
04

Comparing Phenotype Traits

The exercise states that the phenotype trait of an \(Aa\) heterozygous individual is the same as that of an \(AA\) homozygous individual. This means that the \(A\) allele in the \(Aa\) heterozygous individual is responsible for the expressed phenotype.
05

Identifying the Recessive Allele

Based on the information provided, the recessive allele must be one that does not affect the phenotype in the presence of the dominant allele. Since the \(Aa\) heterozygous individual has the same phenotype as the \(AA\) homozygous individual, the \(A\) allele must be dominant. The allele not affecting the phenotype in the presence of the \(A\) allele is the \(a\) allele. Therefore, the \(a\) allele is the recessive allele.

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Most popular questions from this chapter

David Reznick, an ecologist at the University of California at Riverside, studied the process of natural selection in populations of guppies (small freshwater fish) on the island of Trinidad. Reznick found that populations at lower elevations face the assault of predatory fish, whereas the populations at higher elevations live in peace because few predators can move upstream past the waterfalls. The average size of individuals in the higher-elevation waters is larger than the average size of guppies in the lower-elevation populations. Reznick hypothesized that the smaller size of individuals in the lower-elevation populations was a result of increased rates of predation on larger individuals; in effect, predation was selecting for smaller individuals in the population. To test this hypothesis, Reznick moved individuals from the lower elevations to unoccupied pools upstream, where predation was not a factor. Eleven years in these conditions produced a population of individuals that were on average larger than the individuals of the downstream populations. Is the study by Reznick an example of natural selection (does it meet the necessary conditions)? If so, what type of selection does it represent (directional, stabilizing, or disruptive)? Can you think of any alternative hypotheses to explain why the average size of individuals may have shifted through time as a result of moving the population to the upstream (higher-elevation) environment?

Why is natural selection the only process that can result in adaptation?

What is the relationship between an individual's genotype and a phenotype?

What is phenotypic plasticity?

What is natural selection? What conditions are necessary for natural selection to occur?
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