Question

in the following test cross, genes 'a' and 'b' are 20 cm apart, and genes 'b' and 'c' are 10 cm apart: a + c / + b + x a b c / a b c. if the coefficient of coincidence is 0.5 over this interval on the linkage map, how many triply homozygous recessive individuals are expected among 1000 progeny​

Answer 1

Answer:

When genes are linked, new combinations of alleles arise by crossing over between homologous chromosomes during prophase I of meiosis. The frequency of crossover is proportional to the physlcal distance between the loci on the chromosome. The closer two genes (loci) are on the chromosome, the less likely it is that a crossover will occur between them, whereas the farther apart they are, the more likely that a crossover will occur between them. When one crossover has already occurred in a particular region of a chromosome, another crossover in the same region may be inhibited. This inhibition of a second crossover is called interference (I). A related value is called the coefficient of coincidence (C.C.), the proportion of actual double crossovers out of the expected number of double crossovers. The relationship between I and C.C is expressed as I = 1 - C.C.