In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.

Do you expect any of these gene pair(s) to assort independently? Explain your reasoning.

Verified step by step guidance

1. <span>Step 1: Understand the concept of genetic linkage and independent assortment. Genes that are located close to each other on the same chromosome tend to be inherited together, a phenomenon known as genetic linkage. Independent assortment occurs when genes are located on different chromosomes or are far apart on the same chromosome.</span>
2. <span>Step 2: Identify the map positions of the genes on the X chromosome. The gene for body color is at 0.0 m.u., the gene for eye color is at 1.5 m.u., and the gene for bristle form is at 56.7 m.u.</span>
3. <span>Step 3: Calculate the distance between each pair of genes. The distance between the body color and eye color genes is 1.5 m.u. The distance between the eye color and bristle form genes is 55.2 m.u. The distance between the body color and bristle form genes is 56.7 m.u.</span>
4. <span>Step 4: Determine if the genes are likely to assort independently. Genes that are less than 50 m.u. apart are generally considered linked and do not assort independently. Genes that are 50 m.u. or more apart are likely to assort independently.</span>
5. <span>Step 5: Conclude which gene pairs, if any, are expected to assort independently based on their map distances. Consider the threshold of 50 m.u. for independent assortment.</span>

Key Concepts

Gene Linkage

Gene linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. This occurs because linked genes are less likely to be separated by recombination events. In the context of Drosophila, the proximity of the body color gene (0.0 m.u.) and the eye color gene (1.5 m.u.) suggests they are linked, while the bristle form gene (56.7 m.u.) is farther away, indicating a potential for independent assortment.

Independent Assortment

Independent assortment is a principle of genetics that states that alleles of different genes segregate independently of one another during gamete formation. This principle applies to genes located on different chromosomes or those that are far apart on the same chromosome. In the case of the Drosophila genes mentioned, the body color and eye color genes are close together, suggesting they may not assort independently, while the bristle form gene, being much farther away, may assort independently.

Map Units (m.u.)

Map units (m.u.) are a unit of measurement used in genetics to describe the distance between genes on a chromosome, with one map unit equivalent to a 1% chance of recombination occurring between two genes. In the Drosophila example, the distances between the body color and eye color genes (1.5 m.u.) and the bristle form gene (56.7 m.u.) indicate their relative positions and likelihood of being inherited together. Smaller distances suggest a higher likelihood of linkage and lower chances of independent assortment.