Which of the following correctly describes the relationship between the distance between genes on a chromosome, crossing over, and recombination frequency?
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A The closer together two genes are, the more likely a crossover between them will happen, and recombination frequency approaches 1.0.
B The closer together two genes are, the less likely a crossover between them will happen, and recombination frequency approaches 0.
C The closer together two genes are, the less likely a crossover between them will happen, and recombination frequency approaches 1.0.
D The closer together two genes are, the more likely a crossover between them will happen, and recombination frequency approaches
The correct answer and explanation is :
The correct answer is B: The closer together two genes are, the less likely a crossover between them will happen, and recombination frequency approaches 0.
Explanation:
The relationship between gene distance, crossing over, and recombination frequency is a fundamental concept in genetics, especially in the study of genetic mapping.
- Crossing Over and Recombination:
- Crossing over occurs during meiosis, when homologous chromosomes exchange segments of DNA. This results in the creation of recombinant chromosomes, which have a combination of genetic material from both parents.
- The frequency of recombinant chromosomes is called the recombination frequency. This frequency reflects how often crossing over occurs between two genes. A higher recombination frequency means that the genes are more likely to be separated by crossing over, and a lower recombination frequency means that crossing over happens less frequently between those genes.
- Gene Distance and Crossing Over:
- When genes are located far apart on a chromosome, there is a greater chance that a crossover will occur between them. This is because there is more chromosomal material between them that can undergo recombination.
- When genes are located close to each other on the chromosome, the likelihood of a crossover happening between them decreases because they are physically close together. The probability of crossover is lower, and thus the recombination frequency approaches 0.
- Recombination Frequency:
- Recombination frequency is proportional to the distance between two genes on a chromosome. It is typically expressed as a percentage, where a recombination frequency of 1% equals 1 centimorgan (cM), a unit of genetic distance.
- If two genes are very close to each other, the recombination frequency will be low (approaching 0), meaning they are less likely to be separated by crossing over.
- On the other hand, if two genes are far apart, their recombination frequency will be higher (approaching 50%), which is the theoretical maximum frequency for genes that are located on different chromosomes or far apart on the same chromosome.
In summary, the closer two genes are, the less likely a crossover will occur between them, and the recombination frequency approaches 0. This is because crossing over is less likely to happen when genes are in close proximity on the chromosome.