Question

In a testcross involving F1 ​dihybrid flies, more parental type offsprings were produced than the recombinant type offsprings. This indicates that
A. The two genes are located on two different chromosomes.
B. Chromosomes failed to separate during meiosis.
C. The two genes are linked and present on the same chromosome.
D. Both of the characters are controlled by more than one gene.

Answer 1

Hint:-Test cross is done to identify the genotype of an unknown organism by crossing it with the genotype of the known organisms. It was used to find out whether the dominant phenotype had homozygous alleles or heterozygous alleles. When a cross is done then the offspring obtained belong to the F1 generation.

Complete step-by-step solution:-
Crossing over is the exchange of chromosomes between the non-sister chromatids during meiosis.
Crossing over creates new variations that are different from the parent and hence it leads to genetic diversity.
In linkage, the chromosome tends to remain attached to each other. Hence, showing no crossover or independent assortment. So they produce only parental combinations only.
When genes are located on different chromosomes then they need crossing over to produce offspring. So recombinant type offspring are formed in this condition.
If the chromosome fails to separate during meiosis then it would lead to abnormalities in the offspring formed.
If both the characters are controlled by more than one gene then we can’t say anything about the recombinant formed or the parental offspring formed as they need crossing over or linkage to occur.
So the answer is option c ‘ two genes are linked and present in the same chromosome’.

Note:-
Linkage ensures that genes stay together whereas, crossing over ensures segregation of genes. The strength of linkage is inversely proportional to the distance between genes in the chromosome. In crossing over it is directly proportional. In linkage parental offspring are formed whereas, in crossing over the recombinants are formed.