Human chromosomes, consisting of DNA and histones, are primarily located in the nucleus and number 46 (23 pairs) in total. They play a crucial role in cell division, ensuring DNA integrity and proper distribution; any abnormalities can lead to serious conditions like cancer or genetic disorders. Reproductive cells contain a single set of chromosomes, which combine during reproduction to form a complete set in the offspring.

1. Human Molecular Genetics-
Understanding Chromosome Structure
and Function
Summary:
• Chromosomes have unique thread-like structure, made of protein,
called histones and a single
• molecule of deoxyribonucleic acid (DNA). These are mainly located
inside the nucleus but
• can also be found outside the nucleus, as in mitochondria. There are
23 pairs of chromosomes
• found in human body, so the total number of chromosomes is 46.

2. • Chromosomes have unique thread-like structure, made of protein,
called histones and a single molecule of deoxyribonucleic acid (DNA).
These are mainly located inside the nucleus but can also be found
outside the nucleus, as in mitochondria. There are 23 pairs of
chromosomes found in human body, so the total number of
chromosomes is 46.
• Chromosomes in human, other animals and plants are linear in
structure, which is arranged in pairs inside the cell-nucleus. Only
human reproductive cells or gametes have just one copy of each
chromosome that during the reproduction unites with another
reproductive cell and become a single cell, which have two copies of
each chromosome.

3. • Located inside the nucleus of plant and animal cells, chromosomes
have unique thread-like structure, made of protein, called histones
and a single molecule of deoxyribonucleic acid (DNA). The name
chromosome comes from two Greek words – chroma (colour) and
soma (body).
• For a living organism to develop and function the right way, cells
constantly divide into new cells and replace the old ones. During this
process, it is indispensable for DNAs to remain intact to be evenly
distributed among cells. Chromosomes ensure that DNA is properly
copied and distributed during this vast range of cell divisions.

4. Pic 1: Structure of Chromosome

5. • Pic 1: Structure of Chromosome
• Even minor changes in structure and number of chromosomes during the formation of new cells
can lead to serious issues. For example, in human body, cancer is caused by faulty chromosomes,
which are made up of broken chromosomes. The same is for the reproductive cells, like eggs or
sperms to have the right number and structure of chromosomes. Otherwise, the offspring will not
grow properly. For example, children with Down syndrome have 3 copies of chromosome 21
instead of 2 copies found in normal babies.
• Chromosomes in human, other animals and plants are linear in structure, which is arranged in
pairs inside the cell-nucleus. Only human reproductive cells or gametes have just one copy of
each chromosome that during the reproduction unite with another reproductive cell and become
a single cell, which have two copies of each chromosome.
• Besides the liner structure of chromosomes, human or other organisms also have much smaller
type of chromosome. In mitochondria, there is circular chromosome, found outside the nucleus
and serve as the powerhouse of cells.

6. • There are 23 pairs of chromosomes found in human body, so the total
number of chromosomes is 46.
• In human body, one copy of each chromosome is inherited from the
male parent and female parent and is joined into one pair in the
child’s cell. The single cell then divides gradually for numerous times
until the production of a mature individual with a full set of 23 paired
chromosomes. As DNA is passed from the parents, children inherit
some traits of their parents.
• The study of gene and chromosomes has gained much better
understanding since 1990s through the pioneering researches of
Thomas Hunt Morgan. In recent past, with the advent of genetic
engineering, biotechnology, and other genomic studies, this has
gained far better momentum.

7. KEY POINTS:
• 1.Chromosomes have unique thread-like structure, made of protein, called
histones and a single molecule of deoxyribonucleic acid (DNA).
• 2.These are mainly located inside the nucleus but can also be found outside
the nucleus, as in mitochondria.
• 3.There are 23 pairs of chromosomes found in human body, so the total
number of chromosomes is 46.
• 4.Chromosomes in human, other animals and plants are linear in structure,
which is arranged in pairs inside the cell-nucleus.
• 5.Only human reproductive cells or gametes have just one copy of each
chromosome.
• 6.Even minor changes in structure and number of chromosomes during the
formation of new cells can lead to serious issues.