Explain why a 50 percent recovery of single-crossover products is the upper limit, even when crossing over always occurs between two linked genes?

Key Concepts

Single-Crossover Events

A single-crossover event occurs when two homologous chromosomes exchange genetic material at one specific location. This process results in the formation of recombinant and non-recombinant chromosomes. However, because only one crossover event can occur between two linked genes, the maximum recovery of recombinant products is limited to 50 percent, as half of the gametes will still carry the parental combinations.

Linked Genes

Linked genes are genes that are located close to each other on the same chromosome and tend to be inherited together. The closer the genes are, the less likely they are to be separated by recombination during meiosis. This linkage affects the frequency of crossover events, as the probability of a crossover occurring between two linked genes is lower than between unlinked genes, further contributing to the 50 percent recovery limit.

Recombination Frequency

Recombination frequency is the measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is expressed as a percentage, with a maximum of 50 percent indicating that the genes are either unlinked or very far apart. In the case of linked genes undergoing single crossovers, the recombination frequency cannot exceed 50 percent, as this reflects the maximum possible recovery of recombinant types from a single crossover event.