1. Cell division in sexual reproduction
Learning objectives: understand that cells undergo meiosis to produce gametes and describe the process describe how the behviour of the chromosomes in meiosis results in gametes with a single set of genetic information fertilisation of gametes during sexual reproduction results in variation in a species

2. Cell division in sexual reproduction
How many chromosomes are there in new human body cells produced by mitosis?
46 chromosomes
(23 matching pairs)
How many chromosomes are there in human sex cells?
23 unpaired chromosomes
23 unpaired chromosomes

3. Cell division in sexual reproduction
Human sex cells have a set of 23 unpaired chromosomes - that’s half the usual number.
Sex cells in animals and plants follow the same rules.
They have half the usual number of chromosomes.
They have a complete set of single chromosomes.
Why is this important for fertilisation and reproduction?

4. Cell division in sexual reproduction
Sex cells have half the usual number of chromosomes.
Sex cells have to be produced by a special type of cell division.
Sex cells are produced by meiosis.
In which organs does meiosis take place?

5. Cell division in sexual reproduction
Production of male gametes
Did you know…
Around 400 million sperm are produced every 24hrs!
Only one sperm fertilises an egg but it must travel times its own body length to reach it!

6. Cell division in sexual reproduction
Meiosis in cat ovaries
Production of female gametes
Meiosis in plant ovary (lilies)

7. Cell division in sexual reproduction
Meiosis begins with a single cell.
original
cell
First the cell makes a copy
of each chromosome.
first
division
Now, there are two stages of cell division…
second
division
How many chromosomes do the new cells have compared to the original?
4 new cells

8. Cell division in sexual reproduction
meiosis video
...and another one just for fun! (start at 1 min 20 sec)
Meiosis produces four new sex cells with half the original number of chromosomes.
In animals, meiosis produces ova in females and sperm cells in males.
In plants the gametes produced by meiosis are pollen grains (male) and ovules (female).
Meiosis is also called reduction division.
What does this mean?

9. Cell division in sexual reproduction
Comparing mitosis and meiosis:
Complete the table to show the differences:
Mitosis
Meiosis

10. Cell division in sexual reproduction
Comparing mitosis and meiosis:
Complete the table to show the differences:
Mitosis
Meiosis
daughter cells genetically identical
daughter cells genetically different
two cells produced
four cells produced
one cell division
two divisions
cells have full chromosome number
cells have half the chromosome number
body cells for growth, repair, replacement
gametes for sexual reproduction

11. Cell division in sexual reproduction
The importance of meiosis:
Introduces variation by the production of gametes that have half the number of chromosomes than body cells.
Allows mixing of genetic information during fertilisation.

12. û ü ü û û ü û û ü ü True or false?
All cells in the body have 2 sets of chromosomes
Meiosis happens in the reproductive organs only
DNA is copied before cell division starts
In meiosis there is only one cell division
Mitosis introduces genetic variation to a species that reproduces sexually
Variation occurs when gametes from two parents are combined during fertilisation
Gametes have the full number of chromosomes
Mitosis occurs in the testes of animals to produce sperm cells
The male gamete of a sexually reproducing plant is a pollen grain
Meiosis in human females produces ova (eggs) with 23 chromosomes inside û ü ü û û ü û û ü ü

13. Cell division in sexual reproduction
Learning objectives – review: understand that cells undergo meiosis to produce gametes and describe the process describe how the behviour of the chromosomes in meiosis results in gametes with a single set of genetic information fertilisation of gametes during sexual reproduction results in variation in a species