Raymond Popp studied linkage among genes for pink eye (p),...

Raymond Popp studied linkage among genes for pink eye $(p),$ shaker-1 $(s h-1,$ which causes circling behavior, head tossing, and deafness), and hemoglobin $(H b)$ in mice (R. A. Popp. 1962. Journal of Heredity 53:73-80). He perfor med a series of testcrosses, in which mice heterozygous for pink eye, shaker-1, and hemoglobin 1 and 2 were crossed with mice that were homozygous for pink eye, shaker- $1,$ and hemoglobin 2 $$\frac{P S h-1 H b^{1}}{p s h-1 H b^{2}} \times \frac{p s h-1 H b^{2}}{p s h-1 H b^{2}}$$ The following progeny were produced. (TABLE CANNOT COPY) a. Determine the order of these genes on the chromosome. b. Calculate the map distances between the genes. c. Determine the coefficient of coincidence and the interference among these genes.

Raymond Popp studied linkage among genes for pink eye $(p),$ shaker-1 $(s h-1,$ which causes circling behavior, head tossing, and deafness), and hemoglobin $(H b)$ in mice (R. A. Popp. 1962. Journal of Heredity 53:73-80). He perfor med a series of testcrosses, in which mice heterozygous for pink eye, shaker-1, and hemoglobin 1 and 2 were crossed with mice that were homozygous for pink eye, shaker- $1,$ and hemoglobin 2 $$\frac{P S h-1 H b^{1}}{p s h-1 H b^{2}} \times \frac{p s h-1 H b^{2}}{p s h-1 H b^{2}}$$ The following progeny were produced. (TABLE CANNOT COPY)
a. Determine the order of these genes on the chromosome.
b. Calculate the map distances between the genes.
c. Determine the coefficient of coincidence and the interference among these genes.

Key Concepts

Coefficient of Coincidence

The coefficient of coincidence is a ratio used to compare the observed number of double crossover events to the expected number if crossover events occurred independently. It assists in assessing whether crossover events in one region affect the likelihood of a second crossover in a nearby region.

Genetic Interference

Genetic interference quantifies the extent to which a crossover event in one region of a chromosome inhibits or promotes another crossover nearby. It is calculated as one minus the coefficient of coincidence and reflects the degree to which crossover events are not independent of each other.

Recombination Frequency

Recombination frequency is a measure of how often a crossover event occurs between two genes during meiosis. It is calculated as the percentage of recombinant offspring produced in a cross, and it serves as an estimator of the physical distance between genes on a chromosome.

Map Units (Centimorgans)

Map units, or centimorgans (cM), are the units used to express the distance between genes on a chromosome in a genetic map. One centimorgan represents a 1% chance of a crossover event occurring between two genes, making it a useful metric for quantifying genetic linkage.

Gene Mapping

Gene mapping is the process of determining the ordered positions of genes on a chromosome and their relative or absolute distances. This is typically achieved by analyzing recombination frequencies obtained from genetic crosses, which allows researchers to construct linkage maps that represent these relationships.

Genetic Linkage

Genetic linkage refers to the phenomenon where genes that are located close to each other on the same chromosome tend to be inherited together during meiosis. This occurs because the physical proximity decreases the likelihood of recombination (crossing over) between them, leading to non-independent segregation of alleles.

Testcross

A testcross is a genetic cross performed between an individual with an unknown genotype (usually heterozygous for certain traits) and an individual that is homozygous recessive for those traits. This method is used to determine the genotype of the unknown parent by analyzing the phenotypes of the offspring.

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