Meiosis involves TWO
divisions. In humans it
only happens in the
ovaries and the testes.
Produces cells which have half the
normal number of chromosomes
<--- Before the cells starts to
divide, the DNA is duplicated- one
arm of each chromosome is the
exact copy of the other arm.
First Division #1: The chromosome pairs
line up at the center of the cell
First Division #2: The pairs are then pulled apart, so
each new cell has only one copy of each chromosome.
Second Division #1: The chromosomes line up again at
the center of the cell. The arms of the chromosomes are
pulled apart. Like Meiosis, membranes form around each
sets of chromosomes.
You get 4 gametes each with only a single set of
chromosomes in it. From each side of chromosomes, new
nuclei are formed. There is 4 in total
After 2 gametes join at fertilisation, the
zygotes grows by repeatedly dividing by
MITOSIS.
Basic Principles
Gametes have half the usual
number of chromosomes
During Sexual reproduction, the egg
and the sperm combine to form a new
cell called a zygote
All human body cells have 2 copies of the 23
chromosomes (46 total). But gametes only have
one copy of each chromosome (23)
So when the egg and sperm
combine, the zygote will
contain 46 chromosomes- one
set of 23 from each parent