Download cell division

CELLS MAKE COPIES OF THEMSELVES
A NEW LIFE STARTS WHEN GAMETES (SPERM AND EGG CELLS) FUSE.
PRODUCING GAMETES INVOLVES A TYPE OF CELL DIVISION CALLED
MEIOSIS.
IN HUMANS, THIS TAKES PLACE IN REPRODUCTIVE ORGANS.
CELLS IN THE TESTES DIVIDE BY MEIOSIS TO FORM SPERM CELLS.
CELLS IN THE OVARIES DIVIDE BY MEIOSIS TO FORM EGG CELLS.
DURING MEIOSIS, CHROMOSOMES DOUBLE BY COPYING THEMSELVES.
THE CELL THEN SPLITS TWICE TO MAKE 4 NEW CELLS.
Sperm cell
23 chromosomes
Human cell
in testes
46
chromosomes
Sperm cell
23 chromosomes
MEIOSIS
Sperm cell
23 chromosomes
Sperm cell
23 chromosomes
THE GAMETES THAT ARE FORMED CONTAIN ONLY 23 SINGLE
CHROMOSOMES.
A closer look:
What happens to one pair of chromosomes during meiosis?
eg. Forming egg cells:
One of the 23
pairs of
chromosomes
just before cell
division.
Each
chromosome
makes an
identical copy of
itself.
The cell starts to
divide into four.
One chromosome
from each pair
goes into each of
the four sex cells
which are made.
Four eggs each
with 23 single
chromosomes.
THE FIRST CELL OF A NEW BABY IS FORMED WHEN MALE AND
FEMALE GAMETES FUSE AT FERTILISATION. THIS CELL CONTAINS
CHROMOSOMES FROM BOTH GAMETES.
An egg cell with chromosomes
from the mother fuses with a
sperm cell with chromosomes
from the father
A single cell is formed
with pairs of
chromosomes. This
develops into a baby.
THE FERTILISED EGG NOW CONTAINS THE FULL NUMBER OF
CHROMOSOMES.
THERE ARE 46 CHROMOSOMES IN A HUMAN BEING.
YOUR LIFE STARTED STARTED FROM A SINGLE CELL, FORMED BY THE
FUSION OF A SPERM AND EGG.
THIS SINGLE CELL CONTAINED ALL THE GENETIC INFORMATION
NEEDED TO MAKE YOU.
ALL THE THOUSANDS OF CELLS THAT MAKE UP YOUR BODY DEVELOPED
FROM THIS SINGLE CELL BY CELL DIVISION.
DURING CELL DIVISION, ALL THE GENES ARE COPIED INTO NEW CELLS.
The egg has just been
fertilised by a sperm
It copies itself and
divides
It has made 4 new cells
It has become an
embryo
ALL THE CELLS OF YOUR BODY CONTAIN AN EXACT COPY OF THE GENES
THAT WERE IN THE CELL FORMED AT FERTILISATION.
WHEN A CELL DIVIDES A CHROMOSOMES DOUBLE BY COPYING
THEMSELVES. THEN THE CELL SPLITS ONCE TO MAKE 2 NEW CELLS.
Normal human cell
46
chromosomes
Normal human cell
46
chromosomes
MITOSIS
Normal human cell
46
chromosomes
THIS MEANS THAT EACH NEW CELL HAS EXACTLY THE SAME
CHROMOSOMES. THIS TYPE OF CELL DIVISION IS CALLED MITOSIS.
A closer look:
What happens to one pair of chromosomes during mitosis?
eg. Forming egg cells:
One of the 23
pairs of
chromosomes
just before cell
division.
Each
chromosome
makes an
identical copy of
itself.
The cell starts to
divide into two.
One complete set
of chromosomes
goes into each of
the two new
daughter cells.
Two new daughter
cells, each
identical to the
cell they came
from.
CELL DIVISION IS HAPPENING IN YOUR BODY ALL THE TIME TO
REPLACE DAMAGED CELLS AND MAKE NEW ONES SO YOU CAN GROW.
QUESTIONS
1. WHICH TYPE OF CELL DIVISION IS INVOLVED IN MAKING GAMETES?
2. WHICH TYPE OF CELL DIVISION ALLOWS AN EMBRYO TO GROW?
3. HOW MANY CHROMOSOMES DO SPERM AND EGGS CELL CONTAIN?
4. HOW MANY CHROMOSOMES DO BODY CELLS CONTAIN?
5. COMPLETE THE VENN DIAGRAM TO SHOW THE DIFFERENCES AND
SIMILARITIES OF MITOSIS AND MEIOSIS:
MITOSIS
BOTH
MEIOSIS