Question

What is meant by ploidy, aneuploidy, euploidy?

How do aneuploidies occur?

What are polyploidies?

What are the different types of variations in composition and arrangements of chromosomes?

What are deletions, duplications, inversions and translocations?

Answer 1

1) Ploidy is the number of sets of chromosomes in a cell, therefore the number of possible alleles for autosomal and pseudoautosomal genes.

Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell has 45 or 47 chromosomes in its place of the 46. It does not include a difference of one or more complete sets of chromosomes.

Euploidy is a condition when a cell and an organism has one or more than one complete set of chromosomes. For example, when a human cell has an extra set of 23 chromosomes, then it is called euploid. It occurs whenever a cell has a multiple of the haploid number of chromosomes. For example, a normal diploid human cell contains 46 chromosomes (2n). on the other hand, if it happens to contain 69 chromosomes (3n), then it would be euploid.

2) An extra or missing chromosome is a cause of genetic disorders, which includes some human birth defects. Aneuploidies originates during the process of cell division when the chromosomes do not separate properly between the two cells.

3) Polyploid cells and organisms contain more than two paired homologous sets of chromosomes. Most species Eukaryotes are diploid. They have two sets of chromosomes—one set inherited from each parent.

4) Genetic variation shows differences between members of the same species or those of different species – Allelic variations are due to mutations in particular genes and Chromosomal aberrations are significant changes in chromosome structure. They affect more than one gene. They are also called chromosomal mutations chromosomal mutations.

The different types of variations in composition and arrangements of chromosomes are Deletion, duplication, inversion, and translocation, which show chromosomal structural changes.

5) Deletion occurs when an end of chromosome breaks off. It occurs, when genetic material on the chromosome is lost. It happens anywhere on the chromosome.

Duplication is a particular kind of change, which involve the production of one or more copies of any piece of DNA, including a gene or even an entire chromosome. They arise from an event known as unequal crossing-over, which occurs between misaligned homologous chromosomes during the process of meiosis. Duplications have essential in the evolution of the human genome

An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. It occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric. Paracentric inversions do not include the centromere and both breaks occur in one arm of the chromosome. Pericentric inversions include the centromere and there is a break point in each arm.

Translocation is the movement of chromosome segment from one chromosome to another non homologous chromosome. It occurs when a piece of one chromosome breaks off and is transferred to a new region on another chromosome.