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Ch. 5 - Chromosome Mapping in Eukaryotes
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 5 - Chromosome Mapping in EukaryotesProblem 34b
Chapter 5, Problem 34b

Because of the relatively high frequency of meiotic errors that lead to developmental abnormalities in humans, many research efforts have focused on identifying correlations between error frequency and chromosome morphology and behavior. Tease et al. (2002) studied human fetal oocytes of chromosomes 21, 18, and 13 using an immunocytological approach that allowed a direct estimate of the frequency and position of meiotic recombination. Below is a summary of information [modified from Tease et al. (2002)] that compares recombination frequency with the frequency of trisomy for chromosomes 21, 18, and 13. (Note: You may want to read appropriate portions of Chapter 8 for descriptions of these trisomic conditions.)
Table comparing trisomic chromosomes 21, 18, and 13 with their mean recombination frequencies and live-born frequencies.
Other studies indicate that the number of crossovers per oocyte is somewhat constant, and it has been suggested that positive chromosomal interference acts to spread out a limited number of crossovers among as many chromosomes as possible. Considering information in part (a), speculate on the selective advantage positive chromosomal interference might confer.

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1
Understand the concept of positive chromosomal interference: Positive chromosomal interference refers to the phenomenon where the occurrence of one crossover event reduces the likelihood of another crossover occurring nearby on the same chromosome. This ensures that crossovers are distributed more evenly across the chromosome.
Analyze the data provided: The table shows the mean recombination frequency and the frequency of live-born trisomic individuals for chromosomes 21, 18, and 13. Note that chromosomes with lower recombination frequencies (e.g., chromosome 21) are associated with higher frequencies of live-born trisomic individuals.
Relate recombination frequency to trisomy: Recombination during meiosis helps ensure proper segregation of homologous chromosomes. A lower recombination frequency may increase the likelihood of nondisjunction, leading to trisomy. This suggests that recombination plays a role in reducing meiotic errors.
Speculate on the selective advantage of positive chromosomal interference: By spreading out crossovers more evenly across chromosomes, positive chromosomal interference may reduce the likelihood of nondisjunction. This would enhance the fidelity of chromosome segregation during meiosis, reducing the risk of developmental abnormalities such as trisomy.
Conclude the evolutionary significance: The selective advantage of positive chromosomal interference likely lies in its ability to promote genetic stability and reduce the occurrence of meiotic errors, thereby increasing the likelihood of producing viable offspring with normal chromosomal complements.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Meiotic Errors

Meiotic errors occur during the process of meiosis, where chromosomes are segregated into gametes. These errors can lead to aneuploidy, such as trisomy, where an individual has an extra chromosome. Understanding the frequency and types of meiotic errors is crucial for analyzing their impact on human development and the correlation with chromosomal abnormalities.
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Recombination Frequency

Recombination frequency refers to the rate at which genetic recombination occurs during meiosis, resulting in new allele combinations. It is influenced by factors such as chromosome morphology and the number of crossovers. Higher recombination frequencies can be associated with increased genetic diversity, but also with a higher likelihood of errors, which can lead to conditions like trisomy.
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Positive Chromosomal Interference

Positive chromosomal interference is a phenomenon where the occurrence of a crossover in one region of a chromosome reduces the likelihood of another crossover occurring nearby. This mechanism helps to distribute crossovers more evenly across chromosomes, potentially minimizing the risk of meiotic errors and enhancing genetic stability, which may confer a selective advantage in maintaining healthy offspring.
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Related Practice
Textbook Question

The gene controlling the Xg blood group alleles (Xg⁺ and Xg⁻) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness (EMWX) (Ryan et al., 1999) are closely linked on the X chromosome in humans at position Xp22.3 (the tip of the short arm). A male with EMWX who is Xg⁻ marries a woman who is Xg⁺ and they have eight daughters and one son, all of whom are normal for muscle function, the male being Xg⁺ and all the daughters being heterozygous at both the EMWX and Xg loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children. Create a pedigree that represents all data stated above and in the following table.


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Textbook Question

The gene controlling the Xg blood group alleles (Xg⁺ and Xg⁻) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness (EMWX) are closely linked on the X chromosome in humans at position Xp22.3 (the tip of the short arm). A male with EMWX who is Xg⁻ marries a woman who is Xg⁺ and they have eight daughters and one son, all of whom are normal for muscle function, the male being Xg⁺ and all the daughters being heterozygous at both the EMWX and Xg loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children.

For each of the offspring, indicate whether or not a crossover was required to produce the phenotypes that are given.

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Textbook Question

Because of the relatively high frequency of meiotic errors that lead to developmental abnormalities in humans, many research efforts have focused on identifying correlations between error frequency and chromosome morphology and behavior. Tease et al. (2002) studied human fetal oocytes of chromosomes 21, 18, and 13 using an immunocytological approach that allowed a direct estimate of the frequency and position of meiotic recombination. Below is a summary of information that compares recombination frequency with the frequency of trisomy for chromosomes 21, 18, and 13.

What conclusions can be drawn from these data in terms of recombination and nondisjunction frequencies? How might recombination frequencies influence trisomic frequencies?

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