How Many Pairs of Chromosomes are Found in the Human Cell

Introduction

A chromosome is a long DNA molecule that contains part or all of the genetic material of an organism. A chromosome is made up of DNA and coiled with proteins. Chromosomes are found in the nucleus of each cell and carry genomic information from cell to cell. Chromosomes are also made up of proteins along with DNA that is organised into genes.

DNA

Deoxyribonucleic acid is a long polymeric structure of deoxyribonucleotides. The number of nucleotides present in it mainly defines its length. DNA in structural appearance looks like a helix (right-handed) coiled by two strands having anti-polarity. These two strands are complementary to each other and always follow A-T, C-G base pairing, and vice versa, where "A" stands for Adenine, "T" for thymine, "C" for cytosine, and "G" for guanine.

The coding segment of DNA, called exons and introns, is composed of intervening sequences that do not appear in mature or processed RNA.

DNA is associated with various types of proteins that bind to the phosphate group of DNA.

Pairs of chromosomes in the human body

In humans, among the 23 pairs of chromosomes present, 22 pairs of chromosomes are the same in both males and females, known as autosomes (responsible for somatic characteristics), while the 23rd pair is known as the sex chromosomes (responsible for sex determination).

Pairs of ’X’ and ‘Y’ chromosomes govern the sexes.

Males have only one X chromosome and one Y chromosome with autosomes, whereas females have two X chromosomes with autosomes, and no Y chromosome.

When sperm-bearing X chromosomes fertilise an egg, the resultant offspring become females, and if the sperm fertilises the egg without bearing X chromosomes, it produces male offspring.

Sex determination

The establishment of sex through differential development in an individual at the time of zygote formation is known as "sex determination." The sex-determining mechanism in humans is the XX-YY type.

In many insects, sex determination follows the XO type, just as all eggs have an additional X chromosome besides autosomes.

Chromosomal theory of inheritance

Mendel's result on the inheritance of characters also observed thread-like structures in the nucleus and named their chromosomes.

Chromosomes and genes occur in pairs.

The two alleles of a gene pair are on homologous chromosome sites. Pairing and separation of a pair of chromosomes would lead to the segregation of the pairs that they carry, as stated by two scientists named Sutton and Boveri. This theory was also experimentally verified by Thomas Hunt.

How many genes does a human have?

There are around 20,000 to 25,000 that code for human proteins, but their number varies a lot over a few decades. It has now been established that multiple genes regulate the same bodily characteristic.

Chromosomes play a crucial role in the copying process. Sometimes, while copying chromosomes, they either lose or gain a chromosome, known as monosomy and trisomy, respectively.

What if a person doesn't have 23 pairs of chromosomes?

Having fewer chromosomes causes Down syndrome. An unusual number of chromosomes is rare, and it is common to have one more chromosome than to have less. A person might also have some other problems and diseases.