Question

There are ………. pairs of chromosomes in human beings.

Answer 1

Hint: A chromosome is a long chain of DNA that is highly condensed and coiled around histone proteins to form 3D structures. Chromosomes can be easily seen under a light microscope during the metaphase of cell division when they are most coiled.

Complete Answer:
There are 23 pairs of chromosomes in human beings out of which 22 pairs of chromosomes are autosomes and one pair of chromosomes are sex chromosomes or allosomes consisting of X and Y chromosomes. So, in total there are 46 chromosomes in humans which are arranged in homologous pairs.

During gamete formation, the chromosome number becomes half due to meiosis (equational division) but the ploidy is regained back during fertilization of ovum and sperm. Hence, every human has 46 chromosomes, out of which 23 came from the mother (ovum) and the other 23 from the father (sperm).

Additional information: Let us look at some more details about chromosomes.
- A karyotype is known as an individual’s collection of chromosomes. The image of all the chromosomes is produced in order to look for abnormal numbers or structures.
- Ideogram is the diagrammatic representation of karyotype showing all the morphological features of chromosomes and arranged in the decreasing order of size.
- If there is any abnormality in the number of chromosomes it is known as aneuploidy and can cause serious disorders like Down’s syndrome, Turner’s syndrome, and Klinefelter’s syndrome.
- The first chromosome placed in an idiogram is chromosome 1 as it is the largest chromosome with almost 3000 genes on it.
- The smallest chromosome is chromosome 21.

Note:
- Down’s syndrome is caused by the trisomy of chromosome number 21 which means there are 3 copies of its present.
- Turner’s syndrome is caused by the absence of one of the X chromosomes resulting in the karyotype of 45 chromosomes with XO.
- Klinefelter’s syndrome occurs to the presence of an additional copy of the X chromosome resulting in the karyotype of 47 chromosomes with XXY.