CHROMOSOMES
The
nucleus is a solid ball in the centre of the cell.
It contains rodlike structures called chromosomes.
Each cell has 46 chromosomes or 23 pairs. For each
pair one set of chromosomes are inherited from the
father and the other set from the mother. The set
of chromosomes derived from the mother are known as
the X chromosomes and those from the father are known
as the Y chromosomes. The X chromosome is much bigger
than the Y chromosome. Chromosomes are made of a chemical
known as DNA and certain stretches of it contain heredity
information about us known as genes. DNA and genes
will be explained in the next section.
Sex
cells i.e. the female egg and the male sperm however
contain only 1 set (or 23 chromosomes). Females produce
only eggs with X chromosomes and males produce sperm
with either an X or a Y chromosome. During sexual
reproduction, the egg will combine with the sperm
to form a complete set of chromosomes like our other
cells. A female is born when the X chromosome from
a female is paired with an X chromosome from the male
sperm. This is denoted as XX. A male is born when
the X chromosome from a female is paired with an Y
chromosome from the male sperm. This is denoted as
XY.
