Question

What is chromatin and how can it be remodelled?

What information does chromosome banding provide us?

What is repetitive DNA and how are they organized in the genome?

What is meant by ploidy, aneuploidy, euploidy?

How do aneuploidies occur?

What are polyploidies?

What happens when meiosis does not go according to plan.

Please answer ALL questions

Answer 1

• Chromatins

If the DNA strand in a single human cell were stretched out, it would measure several meters in length. Thus, this strand must coil many times over in order to fit into the cell's nucleus,  To achieve this highly condensed form, the DNA winds itself around proteins called histones, thereby forming a complex known as Chromatin.

Chromatin Remodelling can be done by the following two modifications:

a) ATP- Dependant: i.e. by adding and removing certain organic chemical groups to or from the histones which is ATP dependant. The pattern of binding of theses chemical groups determines whether the DNA wrapped around the histones are transcribed or not.

The chemical groups includes acetyl, Phosphate or methyl groups

b) Covalent histone modifications by specific enzymes, e.g., histone acetyltransferases.

• Chromosome banding

The treatment of chromosomes by different staining procedures to reveal characteristic patterns of horizontal bands like bar codes is called as Chromosome banding.

Each chromosome has a unique banding pattern, a distinctive pattern of dark bands (stained regions) and light bands (unstained regions).

The chromosome Banding provides us with the following Information:

a) The banding patterns lend each chromosome a distinctive appearance so the 22 pairs of human non-sex chromosomes and the X and Y chromosomes can be identified and distinguished without ambiguity.

b) Banding also permits the recognition of chromosome deletions, chromosome duplications and other types of structural rearrangements of chromosomes.

• Repetitive DNA:

A DNA sequences that are repeated in the genome. These sequences do not code for protein.

There are two classes of Repetitive DNA:

a) One class termed highly repetitive DNA consists of short sequences, 5-100 nucleotides, repeated thousands of times in a single stretch and includes satellite DNA.

b) Another class termed moderately repetitive DNA consists of longer sequences, about 150-300 nucleotides, dispersed evenly throughout the genome, and includes what are called Alu sequences and transposons.

• Ploidy

It is the number of sets of chromosomes a species may contain.

For e.g. We as humans we are considered diploid as w have carry two sets of Chromosomes.

Aneuploidy: Changes in chromosome number that occurs by the addition of all or part of a chromosome is called Aneuploidy

Euploidy: The gain of one or more complete sets of chromosomes is called Euploidy.
it usually occurs frequently in plants, rarely in animals can lead to formation of new species.

• Aneuploidy usually occurs as trisomy (2n + 1), monosomy (2n - 1).

• Polyploidy refers to a numerical change in a whole set of chromosomes. They are cells and organisms that contain more than two paired (homologous) sets of chromosomes.

• Meiosis is a type of cell division that makes sex cells or gametes.

Errors during meiosis i.e. if it does not go according to plan, can lead to mutations in gametes. Defective gametes that undergo fertilization may result in miscarriages or ultimately lead to genetic disorders.

One of the most common errors during meiosis is Non-disjunction. Non-disjunction occurs when the chromosomes fail to separate properly as the cell divides. A sperm or egg cell may contain an extra chromosome (for a total of 24) or may be missing a chromosome (totalling 22). In humans, this would lead to a person with 47 chromosomes or 45 chromosomes. A pregnancy occurring after non-disjunction could also result in a miscarriage or stillbirth.