Question

In a testcross involving F1 dihybrid flies, more parental-type offspring were produced than recombinant-type offspring. This indicates

• A. Chromosomes failed to separate during meiosis
• B. Both of the characters are controlled by more than one gene
• C. The two genes are linked and present on the same chromosome
• D. The two genes are located on two different chromosomes

Answer 1

The correct option is C

The two genes are linked and present on the same chromosome

The correct option is C.

Explanation of the correct option:

1. Morgan proposed that flies with recombinant features develop as a result of the separation of genes.
2. Morgan postulated that the separation of linked genes occurs due to the formation of chiasmata which represents the point of genetic exchange.
3. He used the term crossing over to describe the physical exchange leading to recombination.
4. Morgan also proposed that two genes located relatively close to each other along a chromosome are less likely to have a chiasma between them as compared to the genes which are located at a greater distance on the chromosome.

Explanation of the incorrect options:

Option A:

1. If the chromosome fails to separate during meiosis, the resulting progeny will be abnormal.

Option B:

1. If both traits are controlled by more than one gene, we can't say anything about the resulting recombinant or parental offspring because they require crossing over or linking to occur.

Option D:

1. When genes are on different chromosomes, they must cross over to make offspring.
2. In this circumstance, recombinant offspring are created.

Final answer: More parental-type offsprings are produced as the two genes are linked and present on the same chromosome.