Question

How many pairs of chromosomes do a human body cell have?

Answer 1

The genetic material of humans- DNA, is packed into thread-like structures called chromosomes. They are located inside the nucleus of cells and carry genetic information about the organisms.

Complete answer:
DNA is a molecule that contains two polynucleotide chains that run anti-parallel to each other and contains the genetic code of an organism. A sequence of nucleotides on DNA forms a gene- the functional unit of heredity and inheritance. The information of DNA is stored in genes. The long-stranded DNA molecules are twisted, condensed, and packed to form chromosomes in a cell. Chromosomes are thread-like structures made up of DNA and proteins that are present inside the nucleus of a cell and carry genetic information from one generation to another. They also play an important role in heredity and variation, mutation, cell division, etc. The DNA is packed many times around the histone to form chromosomes. The residues of amino acids- lysine and arginine form the basic protein- Histone. The negatively charged DNA coils around eight positively charged histone proteins to form a nucleosome. The strand of nucleosomes folds up to form chromatin fiber. Chromatin fibers are tightly packed to form chromosomes.

Humans are diploid organisms that have 46 chromosomes. These chromosomes are paired into 23 pairs of homologous chromosomes that are identical to each other in shape and size and are called homologues of each other. These homologous chromosomes have the same pattern of light and dark bands. The human gametes are haploid and contain only 23 chromosomes. During sexual reproduction, the male and female gametes combine to form the diploid zygote. Thus, in a pair of a homologous chromosome, one copy comes from the paternal side and the other from the maternal side.

Among these 23 pairs of chromosomes, 22 pairs of chromosomes are autosomes and are responsible for the inheritance of all characteristics except the sex-linked. The last pair of these 23 chromosomes is the allosomes or sex chromosomes that provide sex-linked characteristics and are responsible for the biological sex of an individual. X and Y are the two sex chromosomes. XX pair is found in the females, while XY is found in the males. X and Y chromosomes are not homologues of each other and differ in shape, size, and genes. Therefore, human chromosomes can be written as- 44+XX or 44+XY.
An individual’s collection of chromosomes to study chromosome structure and study its abnormalities is called a karyotype.

Note: Chromosomal abnormalities occur in individuals when they have an extra copy of a chromosome or a missing copy of a chromosome, or when a part of the chromosome is broken, deleted, or duplicated. Example- Klinefelter syndrome- 44+XXY, Turner Syndrome- 44+XO, Down syndrome- trisomy of 21st chromosome, etc.