Question

Genetic mapping assumes that recombination can occur at any point along a chromosome with equal probability. True or False?

Answer 1

The statement that genetic mapping assumes recombination occurs with equal probability along a chromosome is false. Recombination hotspots and varying propensities for recombination across the genome's different regions lead to unequal probabilities for recombination events.

Step-by-step explanation:

The statement that genetic mapping assumes recombination can occur at any point along a chromosome with equal probability is False. In the construction of a chromosome map, while Sturtevant initially assumed that recombination could occur with equal likelihood anywhere along the chromosome, subsequent research has shown that certain regions known as recombination hotspots have a higher frequency of recombination, whereas other regions show less propensity for recombination. Thus, the probability of recombination is not uniform along the length of a chromosome.

Sturtevant's genetic maps utilized the concept of recombination frequency to estimate genetic distances between genes on a chromosome. The recombination frequency reflects the average number of crossovers between two alleles and correlates with their genetic distance from each other. With map units or centimorgans (cM) as the measurement, a recombination frequency of 0.01 corresponds to a 1cM distance, with a recombination frequency between 0% and 50% indicating genes linked on the same chromosome. But accuracy diminishes as genetic distances approach a recombination frequency of 0.5, as it becomes difficult to discern if genes are very far apart on the same chromosome or on different chromosomes, since it reaches the threshold where genes are considered essentially unlinked.

Therefore, while genetic mapping is based on the frequencies of recombination, it's crucial to consider multiple methods for developing mapping information to account for natural variances in recombination rates across the genome.

Answer 2

The statement that genetic mapping assumes recombination can occur at any point along a chromosome with equal probability is false. While this assumption was foundational for early chromosome mapping, in reality, recombination rates can vary due to hotspots and genomic regions less prone to recombination. False is the correct answer.

Step-by-step explanation:

Genetic mapping indeed assumes that recombination can occur at any point along a chromosome with equal probability; however, this is not entirely accurate in reality. Alfred Sturtevant, in constructing chromosome maps, postulated that recombination frequency—the average number of crossovers between two alleles—correlated with their genetic distance from each other.

This meant that more distant alleles had a higher chance of recombining since there was a larger region over which recombination could occur. Nearby alleles, on the other hand, were likely to be inherited together.

Sturtevant represented alleles in a linear map and defined genetic distances in map units or centimorgans (cM). A recombination frequency of 0.01 would correspond to a distance of 1 cM. While genes could range from being perfectly linked (recombination frequency = 0) to perfectly unlinked (recombination frequency = 0.5), this model assumes uniform recombination along the chromosome.

However, real-world observations have shown that some parts of the genome are recombination hotspots, while others are less prone to recombination, which challenges the equal probability assumption.

In summary, the initial statement is False because although genetic mapping assumes an equal likelihood of recombination along chromosomes, practical evidence reveals that this is not the case due to the presence of recombination hotspots and regions with low recombination activity.