Question

What is the original source of variation among the different alleles of a gene?

Short answer

The genetic variability is mainly caused because of the different kinds of alleles on the genes. Organisms having more chromosomes will have a higher number of genes as well as alleles.

Grasshopper has more chromosomes and so will have more genes and alleles; the greater number of genes and alleles will bring more variation in an organism.

Therefore, grasshopper (diploid number of chromosomes are 46) will have higher genetic variability when compared with the fruit fly (diploid chromosome number is 8).

Step-by-step solution

Independent assortment

Independent assortment of chromosomes is one of the aspects of sexual reproduction that produces genetic variations. The genetic variation is caused due to random arrangement of homologous chromosomes at the equatorial plate in meiosis I.

The homologous pairs include one paternal chromosome, and the other is a maternal chromosome. The meiotic division leads to the formation of maternal and paternal homologs into the offspring cells independently.

Random fertilization

Random fertilization also brings variations in animals and plants. When there is a fusion of gametes, and at the time of fertilization, the zygote with a higher number of combinations is produced, which will bring variability in living beings.

Number of combinations in fruit fly and grasshopper

The number of possible arrangements of the chromosomes depends on a haploid number of chromosomes. The fruit fly has four haploid chromosomes; the possible number of chromosomes found in the fruit fly is 2⁴, that is, 16 chromosomal arrangements.

A grasshopper with 23 haploid chromosomes will give a number of possible chromosome arrangements, that is, 2²³or 8.4 million possible combinations.