If the cross described in Problem 18 were made, and if Sb and cu are 8.2 map units apart on chromosome III, and if 1000 offspring were recovered, what would be the outcome of the cross, assuming that equal numbers of males and females were observed?

Key Concepts

Genetic Mapping

Genetic mapping is a method used to determine the location of genes on a chromosome and the distance between them. The distance is often measured in map units, where 1 map unit corresponds to a 1% chance of recombination occurring between two genes during meiosis. In this case, the distance of 8.2 map units between the Sb and cu genes indicates a relatively low frequency of recombination, which affects the expected offspring ratios.

Recombination Frequency

Recombination frequency refers to the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated as the number of recombinant offspring divided by the total number of offspring. In the context of the question, a recombination frequency of 8.2% suggests that 8.2% of the offspring will exhibit recombinant phenotypes, while the remaining 91.8% will show parental phenotypes.

Offspring Ratios in Genetic Crosses

In genetic crosses, the expected ratios of offspring phenotypes can be predicted based on the principles of inheritance and recombination. For a cross involving linked genes, the expected outcome can be calculated by considering both parental and recombinant types. Given the recombination frequency and the total number of offspring (1000), one can determine the expected number of each phenotype, which helps in analyzing the results of the cross.