Recombination and Genetic Mapping

Question 1

Recombination frequency

Answer 1

% of recombinant chromosomes

rf = recombinant genotypes
———————————– x 100%
parental + recombinant

• With independent assortment, rf is expected to equal 50%
• Max. value of rf = 50%

Question 2

Where does recombination occur?

Answer 2

In meiosis - during independent assortment
when crossing over

Question 3

What determines recombination frequency between genes?

Answer 3

The distance between genes
The more distance the more likely

Question 4

What could recombination frequency measure?

Answer 4

Distance between genes
- Reflects the frequency of crossover between genes as we can’t detect them directly

Estimate chiasma freq. from recombination freq
Can build up a map to show order of genes on a chromosome + distance between them

Question 5

What does the overall RF depend on?

Answer 5

In a population of meiocytes - depends on the relative proportion of 2 possibilities

Question 6

Chances of recombination

Answer 6

Less than 50% when genes are linked on the same chromosome

• Except for genes very far apart on the same chromosome (rf can be 50%)

Question 7

what is ‘m’?

Answer 7

The average number of cross overs in a interval in a single mitosis

Alfred Sturtevant defined a length of chromosome with m=1 to be map units (50 mu) called centiMorgans

Over short intervals 1% rf = 1 cM