Question

Dimples result from a dominant gene, and a lack of dimples results from a recessive gene. Based on the information in the passage, which of the following will be true for an individual who is a hybrid? A. That individual will have dimples. B. That individual has an equal chance of either having or not having dimples. C. That individual will have a dimple on one side of his or her face, but not on the other. D. That individual will have no dimples

Short answer

A. That individual will have dimples.

Step-by-step solution

Understanding dominant and recessive genes

A dominant gene is the one that will always be expressed when present in an individual, while a recessive gene is the one that is expressed only when there is no dominant gene present. In this case, dimples are a result of a dominant gene, and the lack of dimples results from a recessive gene.

Defining hybrid

A hybrid refers to an individual possessing one dominant gene and one recessive gene, denoted by different letters. In this case, we can denote the dominant gene (dimples) by D and the recessive gene (no dimples) by d. A hybrid individual would have the genes Dd.

Determining the phenotype of a hybrid

Since D (dimples) is the dominant gene and the hybrid individual has one dominant gene (D) and one recessive gene (d), the dominant gene (D) will always be expressed in the individual. This means that the individual will have dimples. Solution: Based on our understanding of dominant and recessive genes and the concept of hybrid, the correct answer is: A. That individual will have dimples.

Key concepts

Dominant and Recessive Traits

In genetics, traits that we can observe in an organism are often dictated by dominant and recessive genes. Genes come in pairs, and each half of the pair is called an allele. When we refer to dominant and recessive traits, we're talking about how these alleles interact.

• Dominant genes: These are always expressed if present, even if only one of the alleles is dominant. Think of them as the stronger partner in the genetic duo.
• Recessive genes: These only show their effects if both alleles in the gene pair are recessive. If a dominant allele is present, the recessive trait will not be expressed.

For example, consider the trait for dimples. Having dimples is a dominant trait, represented by the dominant allele (D), while lacking dimples is a recessive trait, marked by the recessive allele (d). This means that any individual with at least one "D" allele will have dimples.

Hybrid Genetics

Hybrid genetics focuses on organisms that have two different alleles for a specific trait—one dominant and one recessive. In the world of genetics, these are called heterozygous organisms. Recall that a dominant allele masks the effect of a recessive one, leading the organism to exhibit the dominant trait. In hybrid situations, here's what happens:

• When one allele is dominant (D) and the other recessive (d), the genotype of the organism is written as Dd.
• Since the dominant allele overshadows the recessive allele, the resulting phenotype—how the organism looks or behaves—will align with the dominant trait.

Applying this to our dimples example, a hybrid individual with one allele for dimples (D) and one for no dimples (d) will, due to the presence of the dominant gene, have dimples.

Phenotype Expression

Phenotype expression refers to the observable characteristics or traits of an organism. This is a great way to understand how genes influence what we see in living beings. Phenotypes are the result of the interaction between an organism's genetic makeup (genotype) and the environment. When examining phenotype expression in the context of dominant and recessive genes:

• Dominant alleles are always expressed in the phenotype if present. So, in a hybrid genotype (e.g., Dd), the phenotype will directly reflect the dominant gene's trait—in this case, the presence of dimples.
• Recessive alleles are only visible in the phenotype when both alleles in the genotype are recessive (e.g., dd).

Therefore, the phenotype provides a window into an organism's genetics, showing us which traits are handed down through generations, influenced by the ruling power of dominant genes.