In strawberries, plants with whiskers dominate over plants without whiskers, and with round fruits over plants with oblong ones. Crossing two plants yields 521-with mustaches and round fruits, 56-without mustaches and round fruits, 59-with mustaches and oblong fruits, 519-without mustaches and with oblong fruits. What are the genotypes and phenotypes of the parents and the distance between genes?
Let’s designate the gene that determines the development of mustaches in strawberries as C, then the gene that causes their absence will be c.
Let’s designate the gene that causes the development of round berries in strawberries as D, then the gene that causes the development of oblong berries will be d.
The splitting of the 10: 10: 1: 1 type obtained in the strawberry progeny is not characteristic of independent inheritance; it indicates the linkage of the C and D genes within the chromosomes of the parent plant. Since a small percentage of offspring still show cleavage of traits, it should be assumed that strawberries form a certain percentage of crossover germ cells.
Let’s find the conditional distance between C and D:
521 + 56 + 59 + 519 = 1155 – the total number of strawberry plants obtained
56 + 59 = 115 – the total number of plants formed by crossover gametes
(115 * 100%) / 1155 = 9.9567 – approximately 1% of all offspring are formed as a result of crossing over.
The distance between C and D is 1 morganida.
Since all traits are observed in the offspring, a conclusion should be drawn about heterozygosity for both traits of both parental plants – СсDd. This strawberry forms a whisker and has round-shaped berries. 99% of the germ cells formed by it are CD and CD.
1% are sex cells formed as a result of crossing – Cd and cD.
Strawberries with whiskers and round fruits (CCDD) – 49.5%;
strawberries without whiskers with oblong berries (ccdd) - 49.5%;
strawberry without a mustache with a round fruit (ccDD) – 0.5%;
strawberries with mustaches and oblong berries (СCdd) – 0.5%.