Question

A plant of 8 feet height is crossed with a plant of 4ft height, in $F_1$ we got a 6 ft height plant. Selfing of this plant gives 1/64 4ft. plants and 1/64 are 8ft. How many pairs of polygenes are controlling this trait?
(a) 4
(b) 3
(c) 2
(d) 6

Answer 1

Hint: The polygenes are the genes that control the polygenic inheritance. Polygenic inheritance is the inheritance in which one single trait is controlled by two or more genes. The genes in this type of inheritance are generally larger.

Complete answer
The height of the plant is included in a monohybrid cross. The monohybrid cross is the cross where the two parents are crossed with each other having a single trait. To study the inheritance of a single allelic pair, the crossing of two organisms having a pure line is done. It includes two types of gametes. Four offsprings are produced. In the first filial generation, all the offsprings obtained will have a similar trait. In the second filial generation, the offsprings obtained will be having different traits.
In a monohybrid cross, the number of polygenes that controls the trait can be done by this formula:
Here 2 parents are taken and are selfed together, the 4 gametes will be obtained.
Similarly, if the selfing is done between the 4 parents then the number of gametes obtained will be 16, and this continues.
To get the total number of gametes obtained, the ${ 2 }^{ n }$ formula is used, where n = the number of parents taken for selfing.
So, for 64 gametes we have to take 4 parents first then we have to undergo the process of selfing.
So, for 4 parents, ${ 2 }^{ n }$ = 4
Therefore, n = 2

So, the correct answer is ‘2’.

Note:
The traits are usually inherited when they are having different traits. For example in the case of humans, the height is the inheritable trait having various genes generally 3 and having 6 alleles. For the person to be tall, he/she must be having all the dominant alleles of height.