Complete question:
The R and S loci are 35 m.u. apart. If a plant of genotype RS/rs is selfed, what progeny phenotypes will be seen and in what proportions
Answer:
- R-/S- = 0.6052
- R-/ss = 0.1443
- rr/S- = 0.1443
- rr/ss = 0.1056
Explanation:
<u>Available data:</u>
- R-S are 35 mu apart
- Cross: RS/rs x RS/rs
First, we need to recognize the parental gametes and the recombinant ones.
Cross:
Parentals) RS/rs x RS/rs
Gametes) RS Parental ⇒ Equal to the parental genotype
rs Parental ⇒ Equal to the parental genotype
Rs Recombinant ⇒ Product of recombination
rS Recombinant ⇒ Product of recombination
We know that genes are 35 MU apart from each other. The map unit is the distance between the pair of genes for which every 100 meiotic products, one of them results in a recombinant one.
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%.
According to this information, if 1 MU = 1% recombination frequency, then
35MU --------- 35% recombination frequency = 0.35
Now, let us calculate the frequency of each gamete type.
35 map units = 35 % of recombination in total
= % Rs + % rS
= 17.5% Rs + 17.5% rS
Now, if the recombination frequency equals 35% then the parental frequency is 100% - 35% = 65%
65 % parental frequency = % of RS + % rs
= 32.5% RS + 32.5% rs
The frequency of each gamete is
- RS ⇒ Parental ⇒ 32.5% (65% / 2) = 0.325
- rs ⇒ Parental ⇒ 32.5% (65% / 2) = 0.325
- Rs ⇒ Recombinant ⇒ 17.5% (35% / 2) = 0.175
- rS ⇒ Recombinant ⇒ 17.5% (35% / 2) = 0.175
F1 Genotypes and Proportions
- RS/RS = 0.325 x 0.325 = 0.1056
- RS/Rs = 2x 0.325 x 0.175 = 0.1137
- RS/rS = 2x 0.325 x 0.175 =0.1137
- rs/rs = 0.325 x 0.325 = 0.10562
- rs/RS = 2x 0.325 x 0.325 = 0.2112
- rs/Rs = 2x 0.325 x 0.175 = 0.1137
- rs/rS = 2x 0.325 x 0.175 = 0.1137
- Rs/rS = 2x 0.175 x 0.175 = 0.061
- Rs/Rs = 0.175 x 0.175 = 0.0306
- rS/rS = 0.175 x 0.175 = 0.0306
F1 Phenotypes and Proportions
- R-/S- = 0.1056 + 0.1137 + 0.1137 + 0.2112 + 0.061 = 0.6052
- R-/ss = 0.1137 + 0.0306 = 0.1443
- rr/S- = 0.1137 + 0.0306 = 0.1443
- rr/ss = 0.1056
