How would the results in cross (a) of Problem 20 vary if...

How would the results in cross (a) of Problem 20 vary if genes $A$ and $B$ were linked with no crossing over between them? How would the results of cross (a) vary if genes $A$ and $B$ were linked and 20 map units apart?

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Key Concepts

Crossing Over

Crossing over is a process during meiosis in which homologous chromosomes exchange segments of genetic material. This recombination event can produce new combinations of alleles. In the context of linked genes, the absence or presence of crossing over directly affects whether the genes are passed on together as a parental type or as recombinant types.

Recombination Frequency and Map Units

Recombination frequency is the measure of how often crossing over occurs between two linked genes, expressed as a percentage. Map units (or centimorgans) are units for the genetic distance between genes, where one map unit corresponds to a 1% recombination frequency. Thus, if genes are 20 map units apart, the recombination frequency is 20%, which alters the expected distribution of allele combinations compared to the situation with no crossing over.

Genetic Linkage

Genetic linkage refers to the tendency of genes that are located close together on the same chromosome to be inherited together, rather than assorting independently as described by Mendel’s law of independent assortment. This concept is crucial because when genes are linked, their inheritance patterns are altered compared to genes on different chromosomes or far apart on the same chromosome.

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