I C S E – Biology
Chromosomes
Chromosome :
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each
chromosome is made of histone proteins and a single molecule of deoxyribonucleic acid (DNA).
DNA contains the specific instructions on their genes that make each type of living creature
unique. Chromosomes pass hereditary information from parents to offspring;
Karyotype :
A karyotype is an individual’s collection of chromosomes and is arranged in pairs based on their
banding pattern and size.
Human Karyotype :
Humans have a total of 46 chromosomes i.e. 23 pairs in each cell, except in
gametes.
 Autosomes :
Each pair of chromosomes other than sex-chromosomes are called
autosomes (chromosome pairs 1-22 are called autosomes) as these are
identical in shape and size. They aid in the growth and repairing of cells.
 Sex-Chromosomes : [ Allosomes ]
a type of chromosome that helps in sex determination are called sexchromosomes. Humans and most other mammals have two sex-chromosomes
(23rd pair). Females have two X-chromosomes in their cells, while males have
both X and Y chromosomes in their cells. Egg cell contains one X chromosome,
while sperm cell contains one X or one Y chromosome. This arrangement
means that it is the male that determines the sex of the offspring when
fertilization occurs.
Centromere
The constricted region of linear chromosomes is known as the centromere. It is located at some
point on the chromosome. The regions on either side of the centromere are referred to as the
chromosome's arms.
Function :
Centromeres help to keep chromatids align properly to spindle fibres during the
process of cell division.
Centromere serves as an attachment site for the two halves of each replicated
chromosome, known as sister chromatids.
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