Question

According to Alfred Sturtevant, what is the relationship between the distance of two genes on a chromosome and the likelihood of a crossover event occurring?

1) The farther apart two genes are on a chromosome, the more likely it is that a crossover event will occur
2) The closer two genes are on a chromosome, the more likely it is that a crossover event will occur
3) The distance between two genes on a chromosome has no effect on the likelihood of a crossover event occurring
4) The relationship between the distance of two genes on a chromosome and the likelihood of a crossover event occurring cannot be determined

Answer 1

Alfred Sturtevant discovered that the greater the distance between two genes on a chromosome, the more likely a crossover event is to occur, with this likelihood quantified by the recombination frequency. This principle is used to construct genetic maps of chromosomes.

Step-by-step explanation:

According to Alfred Sturtevant, the relationship between the distance of two genes on a chromosome and the likelihood of a crossover event occurring is that the farther apart two genes are on a chromosome, the more likely it is that a crossover event will occur.

Sturtevant's work on constructing chromosome maps assumed that genes were ordered serially on chromosomes and that the incidence of recombination could occur anywhere along the chromosome's length with equal likelihood. He noted that alleles that were far apart were more likely to dissociate during meiosis due to the larger region over which recombination could occur. Conversely, alleles that were close to each other on the chromosome were likely to be inherited together. He quantified this relationship using recombination frequency, which correlates with genetic distance, measuring the average number of crossovers between two alleles. This frequency is used to predict distances between genes, resulting in the construction of genetic maps measured in centimorgans (cM).

Answer 2

Sturtevant's work shows the farther apart two genes are on a chromosome, the more likely a crossover event is, quantified by centimorgans, making the correct answer option 1.

Step-by-step explanation:

According to Alfred Sturtevant, the relationship between the distance of two genes on a chromosome and the likelihood of a crossover event occurring is that the farther apart two genes are on a chromosome, the more likely it is that a crossover event will occur.

Sturtevant postulated that genes which are far apart have a higher recombination frequency because there is more space along the chromosome where crossing over could happen. This concept is quantified in units called centimorgans (cM), where a recombination frequency of 0.01 corresponds to 1 cM distance. Therefore, the correct option is 1) The farther apart two genes are on a chromosome, the more likely it is that a crossover event will occur.

Genetic linkage maps created using this information show the relative distances between genes, allowing us to predict how often crossing over may separate them. As the distance between two genes increases, the probability of one or more crossovers between them increases, making them behave as if they were on separate chromosomes.