Question

In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental type as experimentally shown by Morgan and his group?

Answer 1

When two different lines of jeans are featured with their variances into observed rates as setting a cross among themselves it is called a dihybrid cross. Mendel has stated that during a dihybrid cross between two parents, a relationship of completely dominant recessive traits can be observed. In the name of Dihybrid cross, by the name of ‘di’ it is shown that two traits are involved in the cross while each of those traits has two different alleles.

Complete answer:

Morgan chose Drosophila also known as house fly or fruit fly for the experiment. The female Drosophila had a yellow colour body with red coloured eyes. And the male Drosophila had a brown coloured body with red coloured eyes.
In the first-generation ${F_1}$ obtained, it is observed that brown body and red eyes were dominant traits (Bb and Rr). Hence, in ${F_1}$ generation, the genotype was BbRr, which is the traits of the male parent.
Now when two members of ${F_1}$ generation crossed among themselves, the result was 9:3:3:1, that is, out of the 16 phenotypes, 9 had brown body and red eyes, 3 had yellow body and red eyes and other 3 had brown body and white eye. Only one out the 16 phenotypes, got the recessive traits of the female Drosophila.
Hence, Morgan concluded from this experiment that the genes for these character traits (body colour and eye colour) were located in the same chromosome. These genes were claimed to be so close to each other that they have a force of attraction among themselves known as linkage, which means that at the time of segregation, the crossing percentage of these genes decreased considerably. Therefore, during the dihybrid cross between these two categories the ${F_2}$ generation formed the phenotype ratio as 9:3:3:1.

Note: When it is found that the genes are on different loci on a chromosome, the distance between them is less. That is why, in those cases the chances of recombination of genes get higher. It thus flourishes with more varieties of mixed type or utmost non-parental features in the offspring.