GENTICS - Huang1 Genetic Linkage and Mapping in Eukaryotes

- Chi-Square Analysis, Calculating Genetic Map Distance, Calculating Interference

What is the difference in meaning between the terms genetic recombination and crossing over?

Genetic recombination refers to the process by which offspring inherit a combination of genes different from that of either parent, resulting in genetic diversity. Crossing over is a specific mechanism of genetic recombination where homologous chromosomes exchange segments during meiosis, creating new combinations of alleles on each chromosome.

When a chi square test is applied to solve a linkage problem, explain why an independent assortment hypothesis is proposed.

An independent assortment hypothesis is proposed in a chi-square test for linkage to serve as a null hypothesis. It assumes that genes assort independently, meaning no linkage exists. By comparing observed results to this hypothesis, we can determine if deviations are significant, indicating that genes are likely linked.

A diploid organism has a total of 14 chromosomes and about 20,000 genes per haploid genome. Approximately how many genes are in each linkage group?

• Given that the organism has a total of 14 chromosomes, its haploid number is 7.

• There are about 20,000 genes per haploid genome.

To find the approximate number of genes in each linkage group:

Genes per linkage group = (20,000 genes)/(7 linkage groups) = 2,857 genes.

Approximately 2,857 genes are in each linkage group.

A heterozygous individual (Bb) with brown eyes has one eye with a small patch of blue. Provide two or more explanations for how the blue patch may have occurred

The individual might exhibit a patch of blue eye color in an otherwise brown eye color. The bb cells produce blue color, creating a visible sector due to genetic mosaicism caused by mitotic recombination.

If genes X and Y are 25 map units apart on a chromosome, what is the probability that a crossover will occur between them in a single meiosis?

The probability of a crossover occurring between genes X and Y is 25%. In genetic mapping, the map distance in units is equivalent to the percentage chance of a crossover occurring between the genes in a single meiosis.

In a three-point test cross with genes A, B, and C, you observe the following recombinant frequencies: A-B = 10%, B-C = 8%, and A-C = 18%. Based on these distances, what is the most likely order of the genes?

The most likely gene order is A-B-C. The distances add up in this order (A-B = 10%, B-C = 8%, A-C = 18%), fitting the observed recombination frequencies.

Define crossover interference and explain its effect on double crossovers in a given region.

Crossover interference is the phenomenon where the occurrence of one crossover reduces the likelihood of a second crossover occurring nearby. This results in fewer double crossovers than expected based on the recombination frequencies alone.

You observe fewer double crossovers in a region of a chromosome than expected. What does this indicate about the level of interference

This indicates positive interference, meaning that one crossover event is inhibiting the formation of another crossover nearby, reducing the expected number of double crossovers.

In a mapping experiment, the coefficient of coincidence (CoC) is calculated as 0.6 for a specific region. What is the interference value, and what does it suggest about crossover events in this region?

The interference value is calculated as 1 - CoC. So, 1 - 0.6 = 0.4. This positive interference value of 0.4 suggests that there is a 40% reduction in double crossover events in this region compared to the expected number if crossovers were independent.