Answer and Explanation:
Crossing-over between two genes that are very close to each other in the chromosome is not that common. Crossing-over during meiosis occurs random positions all along the chromosome. Then, crossing-over frequency between two genes depends on the distance between them. A short distance between genes is a very little target for crossing-over to occur, which means that only a few of them will happen, compared with the number of events between genes that are more separated between each other.
- Two genes that are very close will have a few recombination events and are strongly bounded.
- Two separated genes will have more chances of recombination and are not bound.
To calculate the recombination frequency, we have to know that 1% of recombinations = 1 map unit = 1cm. And that the maximum recombination frequency is always 50%.
The map unit is the distance between the pair of genes for which the recombination frequency is 1 in 100 meiotic products.
So, en the exposed example:
a.
Identify the gametes for a plant with the genotype DR/dr and label parental and recombinants
Gametes DR parental type
Dr recombinant type
dr parental type
dR recombinant type
Give the frequency of each gamete type.
18 map units = 18 % of recombination in total
= % Dr + % dR
= 9% + 9%
100% - 18% = 82% of parental in total =
= % of DR + % dr
= 41% + 41%
The frequency for each gamete is:
DR 41%
dr 41%
Dr 9%
dR 9%
b.
Identify the gametes for a plant with the genotype Dr/dR
Gametes Dr parental type
DR recombinant type
dR parental type
dr recombinant type
Give the frequency of each gamete type.
18 map units = 18 % of recombination in total
= % DR + % dr
= 9% + 9%
100% - 18% = 82% of parental in total =
= % of Dr + % dR
= 41% + 41%
The frequency for each gamete is:
Dr 41%
dR 41%
dr 9%
DR 9%
