Problem 7 - Biology of Humans: Concepts, Applications, and Issues

Question

How many different gametes could a person with the genotype AaBbCc form? (The genes are on different chromosomes.) a. 2 b. 4 c. 16 d. 64

Step-by-Step Solution

Answer

8 different gametes.

Step 1: Identify Gene Combinations

Each gene has two alleles: A or a, B or b, and C or c. Since the genes are on different chromosomes, they assort independently.

Step 2: Determine Number of Combinations

For each gene, there are 2 possible alleles. The total number of different gametes is the product of the number of alleles per gene.

Step 3: Calculate Total Gametes

Multiply the number of possible alleles for each gene: \[2 \text{ (A/a)} \times 2 \text{ (B/b)} \times 2 \text{ (C/c)} = 8\]

Step 4: Identify the Correct Answer

The number of different gametes a person with genotype AaBbCc can form is 8, which is not directly listed as an option. Ensure the options in the problem are rechecked.

Key Concepts

Independent Assortment

Independent assortment is a key principle of genetics first described by Gregor Mendel. It states that alleles for different genes are distributed to sex cells ("gametes") independently of one another. This is because the genes are located on different chromosomes. During meiosis, the process that forms gametes, chromosomes are randomly segregated into daughter cells, ensuring diverse genetic combinations in the offspring.
For example, in the genotype AaBbCc, each gene pair (A/a, B/b, C/c) can combine independently. Therefore, the formation of gametes involves all possible allele combinations from these genes, contributing to genetic diversity.

Genotype

A genotype is the complete set of genes or alleles an organism carries. It directly influences the organism's traits or phenotype. For example, in the problem's context, the genotype AaBbCc means the organism has two alleles for each gene (A, a for gene 1; B, b for gene 2; C, c for gene 3). These combinations determine which traits will be passed to the offspring. The combination of these alleles through the process of meiosis and independent assortment determines the possible gametes (reproductive cells) that an organism can produce.

Alleles

Alleles are different forms or variations of a gene. Each individual inherits two alleles for each gene, one from each parent. For example, the gene that determines eye color might have an allele for brown eyes and an allele for blue eyes.
In the genotype AaBbCc:

• A and a are alleles for one gene.
• B and b are alleles for another gene.
• C and c are alleles for a third gene.

Different combinations of these alleles result in different traits being expressed in the organism.

Chromosomes

Chromosomes are long strands of DNA containing many genes. Humans have 23 pairs of chromosomes, making a total of 46. Each pair consists of one chromosome from each parent. Genes located on different chromosomes assort independently during meiosis. This means the assortment of alleles is random, contributing to genetic variation.
For example, in the given genotype AaBbCc, the genes responsible for these traits are on different chromosomes. This independent assortment leads to multiple combinations of alleles in the gametes, accounting for the 8 different possible gametes as a result of various allele combinations.