Question

Crossing-over is more likely to occur between genes that are a. close together on a chromosome. b. on different chromosomes. c. far apart on a chromosome. d. loeated on the \(Y\) chromosome.

Short answer

c. far apart on a chromosome.

Step-by-step solution

Understand the concept of crossing-over

Crossing-over is the process where homologous chromosomes exchange segments during meiosis. This increases genetic diversity by producing new combinations of alleles.

Analyze gene placement for crossing-over likelihood

The likelihood of crossing-over between two genes depends on the distance between them on the chromosome. Genes that are farther apart have a higher chance of crossing-over because there is a greater opportunity for breaks to occur between them.

Evaluate option a: close together on a chromosome

Genes that are close together on a chromosome are less likely to be separated by crossing-over events because there is less distance for a break to occur between them.

Evaluate option b: on different chromosomes

Crossing-over only occurs between homologous chromosomes, so it cannot happen between genes located on different chromosomes.

Evaluate option c: far apart on a chromosome

Genes that are far apart on the same chromosome have a higher probability of crossing-over because the larger distance increases the chance of a break occurring.

Evaluate option d: located on the Y chromosome

Crossing-over can occur on any chromosome, but the question isn’t about the likelihood on a specific chromosome like the Y chromosome.

Determine the correct answer

Based on the analysis, the correct answer is that crossing-over is more likely to occur between genes that are far apart on a chromosome.

Key concepts

homologous chromosomes

Homologous chromosomes are pairs of chromosomes that have the same structure and carry the same genes, although they might have different versions of these genes, called alleles. These pairs of chromosomes come from both parents: one chromosome of the pair from the mother and the other from the father. During meiosis, homologous chromosomes line up together, allowing them to exchange genetic material in a process called crossing-over. The alignment and exchange of genetic material ensure that each gamete (sperm or egg cell) has a unique set of genes, contributing to genetic diversity in offspring.

genetic diversity

Genetic diversity refers to the variety of genetic material in a population. It's crucial for the survival and adaptability of species. One key way genetic diversity is achieved is through crossing-over during meiosis. Crossing-over involves the exchange of chromosome segments between homologous chromosomes, creating new combinations of alleles. These new combinations mean that each offspring has a unique genetic makeup, which can be beneficial for adapting to changing environments. Additionally, genetic diversity reduces the chances of inherited diseases spreading through a population.

meiosis

Meiosis is a special type of cell division that reduces the chromosome number by half, creating four gamete cells. Each gamete has half the genetic information of the original cell. It consists of two rounds of division: meiosis I and meiosis II.
During meiosis I, homologous chromosomes pair up and exchange segments in a process known as crossing-over. This generates genetic diversity by mixing up genetic material.
After meiosis I, the cell divides again in meiosis II, separating the sister chromatids into individual cells.

• Meiosis I: Separation of homologous chromosomes and crossing-over.
• Meiosis II: Separation of sister chromatids.

The result is four unique gametes, each with a different combination of genes.

gene location

Gene location on a chromosome plays a significant role in the likelihood of crossing-over. The principle to understand here is that the distance between genes on a chromosome affects how often crossing-over occurs between them.
Genes positioned far apart from each other on the same chromosome have a higher probability of crossing-over. This is because there is more opportunity for the chromosomes to break and exchange segments in the larger space between them.
Conversely, genes that are close together have a lower chance of crossing-over as there is less distance for breaks to occur. Therefore, geneticists often map gene locations by analyzing how frequently crossing-over occurs, which helps them understand gene linkage and inheritance patterns.