Question

The change of chromosomal parts between non homologous pairs of chromosome is
A) Crossing over
B) Translocation
C) Inversion
D) Transition

Answer 1

Hint: Chromosomes are structures that carry genes, our units of heredity. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).

Complete answer:
Chromosomal crossover was described by Thomas Hunt Morgan. It is the exchange of genetic material during sexual reproduction between two homologous chromosomes of the non-sister chromatids, which results in recombinant chromosomes. It occurs in the pachytene stage of prophase I of meiosis during a process called synapsis.
>Translocation occurs when part of a chromosome is transferred to a non-homologous chromosome. It differs from crossing over as it involves non-homologous chromosomes whereas cross over occurs between two homologous chromosomes.
>An inversion is a chromosomal rearrangement in which a part of a chromosome is reversed end to end. This mutation occurs when a single chromosome undergoes breakage, rotates 180 degree and then rejoins with itself.
>Transition is a type of point mutation that changes a purine nucleotide to another purine (A ↔ G), or a pyrimidine nucleotide to another pyrimidine (C ↔ T).
>There are three types of translocations: Reciprocal, non-reciprocal and Robertsonian.
>Reciprocal translocations are exchanges of genetic material between non-homologous chromosomes and are usually harmless and may be found through prenatal diagnosis. Translocation during gametogenesis can result in a chromosomal abnormality that will be present in all cells of the offspring. However, somatic translocation only shows abnormality in the affected cell-line.
>Nonreciprocal translocation is a one-way transfer of genes from one chromosome to another non-homologous chromosome.
>Robertsonian translocation is the most common type of chromosomal translocation in humans. It occurs when two chromosomes join together in an abnormal way. It involves both homologous and non-homologous chromosomes. This type can result in a large arm with a vast majority of its genes, and a short arm with a much lesser proportion of genes.

Thus the correct option is B, ‘Translocation’. This mutation can cause serious disorders like leukemia.

Note:This mutation can result in a lot of diseases like cancer, infertility, Down syndrome (in case of Robertsonian translocation). Translocation is detected during karyotype of the affected cells. Radiations can result in genetic changes due to translocation.