Question

Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to

• A. linkage
• B. repulsion
• C. crossing over
• D. recombination

Hint:

Mendel's law of independent assortment states that the segregation of a trait is independent of the other.

Answer 1

The Correct Option is A

Linkage is the tendency of alleles (belonging to different genes) to be passed together from one generation to another. Genes on the same chromosome can only show linkage. Gene on a non-homologous chromosome is unlinked and always displays linkage. 

William Bateson, ER Saunders and RC Pennett worked with Lathyrus odoratus (sweet pea) in 1905. They were the first to discover linkage, an exception to the law of independent assortment.

Answer 2

Correct option (A) linkage

Explanation: TH Morgan in 1910 explained the lack of independent assortment in Drosophila as a result of linkage. 

• When genes present closely link together in a group and are transmitted as a single unit, the phenomenon is known as linkage.
• Linkage stops the independent assortment process. 
• The incomplete linkage is broken down as a result of crossing over.

Answer 3

Correct option: (A) linkage

Mendel's law of independent assortment states that the segregation of a trait is independent of the other.

1. At the time of the formation of gamete, two alleles belonging to different genes assort independently.
2. Morgan established that genes found on the same chromosome exhibit linkage or physical association.
3. This is why they are inherited together leading to more parental combinations.

Linkage is the phenomenon in which closely located alleles on a chromosome have a tendency to be inherited together during the process of meiosis.

Explanation of the incorrect options:

Option B) Repulsion

Repulsion refers to the tendency of genes on different chromosomes to stay separate.

Option C) Crossing Over 

Crossing over, also referred to as Chromosomal crossover, refers to the exchange of genetic material between non-sister chromatids of two homologous chromosomes during sexual reproduction.

Option D) Recombination

Recombination is the process through which DNA pieces are broken and then recombined to form new allele combinations.

Hence, the lack of independent assortment of two genes A and B in the fruit fly Drosophila is due to linkage.