Waxy endosperm (w x), shrunken endosperm (s h), and yellow...

Waxy endosperm $(w x),$ shrunken endosperm $(s h),$ and yellow seedling $(v)$ are encoded by three recessive genes in corn that are linked on chromosome $5 .$ A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting $\mathrm{F}_{1}$ are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are: (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.

Waxy endosperm $(w x),$ shrunken endosperm $(s h),$ and yellow seedling $(v)$ are encoded by three recessive genes in corn that are linked on chromosome $5 .$ A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting $\mathrm{F}_{1}$ are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are: (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

Gene Linkage

Gene linkage refers to the phenomenon where genes located close to one another on the same chromosome tend to be inherited together rather than assorting independently. This non-independent assortment is due to the physical proximity of the genes and the relative infrequency of recombination events occurring between them during meiosis.

Three-Point Cross

A three-point cross is a genetic experiment involving three genes that allows scientists to determine not only the order of genes on a chromosome but also the distances between them. By analyzing the phenotypes of the offspring, one can deduce which gene is in the middle and estimate the recombination frequencies between adjacent genes.

Recombination Frequency and Map Distances

Recombination frequency is the proportion of recombinant offspring produced in a genetic cross and is directly related to the physical distance between genes on a chromosome. These distances, often measured in centiMorgans (cM), provide a genetic map that estimates how far apart genes are based on the likelihood of crossover events during meiosis.

Coefficient of Coincidence and Genetic Interference

The coefficient of coincidence is calculated by comparing the observed frequency of double crossovers to the expected frequency if crossovers occurred independently. Genetic interference is the impact that one crossover event has on the occurrence of another nearby, often expressed as one minus the coefficient of coincidence. These concepts help in understanding how the occurrence of new genetic combinations is affected by the proximity of genes along a chromosome.

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