Linked genes
Genes close together on the same chromosome tend to be inherited together. Crossing over can separate them. The further apart two genes are, the more often they recombine, so recombination frequency gives a map distance.
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Analogy
Two houses on the same street move together; a long street can split them.
Example
Offspring: 1,000.Recombinants: 80.80 / 1,000 = 8%.Genes are 8 map units apart.
In practice
1 percent recombination equals 1 map unit (centimorgan).
Practice
Flashcards
- What does a recombination frequency of 12% mean?The two genes are about 12 map units apart on the chromosome.
Interview questions
- Describe how recombination frequency is used to map genes and why linked genes break Mendel's second law.
- Linked genes on same chromosome
- Do not assort independently
- Crossing over separates them
- Frequency proportional to distance
Questions people ask
What is a map unit or centimorgan?
A map unit is a measure of distance between genes on a chromosome. One map unit means a 1 percent chance that crossing over separates the two genes in a gamete. The measure is based on how often recombination happens, not on a physical length in base pairs.
Why can recombination frequency never be more than 50 percent?
If genes are far apart, many crossovers occur between them. Multiple crossovers cancel each other out, so recombinants and parental types appear equally, 50 percent each. This is the same as if the genes were on different chromosomes, so the frequency levels off at 50 percent.