Question

The genetic distance between genes A and B is 10 Cm. an organism with Ab combination of the alleles is crossed with the organism with a aB combination of alleles. What will be the percentage of the gametes with AB allele combination produced by an F1 individual?
A.1
B.5
C.10
D.50

Answer 1

Hint: The genetic crossing over is calculated by recombination frequency. Out of their progeny, 10% will be recombinant type and the AB allele represents half of the recombinant type.

Complete answer:
The exchange of DNA between maternal and paternal chromosomes during meiosis, in all multicellular organisms takes place during the process of recombination. When a test cross, between the parental bodies takes place the two recombinant classes always make up 50 percent of the progeny. There is 25 percent of each recombinant type among the progeny. Alleles that are close to each other on the chromosome are likely to be inherited together. The average number of crossovers between two alleles, or their recombination frequency is correlated with the genetic distance from each other. The genetic distance is relative to the locations of other genes on that chromosome.
The genetic distance between genes A and B is 10 cm as given. Therefore, the recombination frequency is 10%. If the cross happens between two parents having genotype Ab and aB, their progeny, 10% will be formed of recombinant type (that is AB and ab) and 90% will be formed parental type (that is aB and Ab). Out of that, 10% AB allele formed, half of the recombination type alleles are formed, that is 5%.

Hence, the correct answer is option (B)

Note: Crossovers during meiosis happen at more or less random positions along the chromosome. The frequency of crossovers between two genes depends on the distance between them. A pair of genes with a larger recombination frequency is far apart, while a pair with a smaller recombination frequency are close to each other.