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• Define meiosis: cellular division for the production of sex cells.
• Occurs in ovaries (produces ovum) and testes (produces sperm)
• Sex cells are haploid (no homologous chromosomes): they contain half
the number of human chromosomes (DNA) as a regular body cell. They
contain only a single copy of each of the 23 different human
chromosomes.
• There will be some variation amongst the chromosomes in sex cells
• Fertilisation: the result of a haploid sperm fusing with a haploid ovum to
produce a diploid cell, that further develops into a baby
• A brief overview of mitosis (taught in Year 8)
• Compare mitosis and meiosis as follows:
Mitosis Meiosis
Where? In all body cells (except to produce the sex cells)
In ovaries or testes
Why? To replace dead cells To produce ovum (in ovaries) and sperm (in testes)
Number of daughter cells produced from one parent cell?
Two Four
Are there homologous pairs in the daughter cells?
Yes No
Are cells produced diploid or haploid?
Diploid Haploid
Is variation produced? No Yes
Recap - Mitosis A fancy word for asexual cell reproduction
One parent cell divides into two identical daughter cells, both with the same DNA as the parent cell.
DNA replicates (copies itself) before one cell becomes two.
Each cell contains two sets of chromosomes (one from each parent, mum and dad) – DIPLOID CELLS
There are five stages of mitosis, also exist in meiosis (but happen twice)
1 - Interphase
http://www.biology101.org/biologystudyguides/whatismitosis.php
• The cell is doing its normal thing.
• The DNA is in the form of Chromatin, inside the nucleus, working away happily
2 - Prophase
http://www.biology101.org/biologystudyguides/whatismitosis.php
• DNA strands duplicate themselves (replication) and remain connected at the centre
• DNA comes together to form chromosomes
1 - Metaphase
http://www.biology101.org/biologystudyguides/whatismitosis.php
• Chromosomes align in the centre
• Spindles from the centrioles at either side grab hold of each chromosome duplicate
1 - Anaphase
http://www.biology101.org/biologystudyguides/whatismitosis.php
• Duplicates are pulled apart into two separate bunches.
• We now have the material to create two identical cells
1 - Telophase
http://www.biology101.org/biologystudyguides/whatismitosis.php
• Each nucleus reforms
• Cell division (cytokinesis) which produces two independent cells which are identical – yaye!
http://www.biology101.org/biologystudyguides/whatismitosis.php
Crash Course – Mitosis https://www.youtube.com/watch?v=L0k-enzoeOM
Meiosis A fancy word for sexual cell production
Only occurs in testes and ovaries
Like mitosis, but occurs twice.
One parent cell divides into four daughter cells
DNA in each of the four daughter cells is different
Unlike mitosis, only half of the DNA is present in the daughter cells – HAPLOID CELLS
There are more stages in Meiosis.
SummaryMitosis Meiosis
Where? In all body cells (except to produce the sex cells)
In ovaries or testes
Why? To replace dead cells To produce ovum (in ovaries) and sperm (in testes)
Number of daughter cells produced from one parent cell?
Two Four
Are there homologous pairs in the daughter cells?
Yes No
Are cells produced diploid or haploid?
Diploid Haploid
Is variation produced? No Yes
Crash Course – Meiosis https://www.youtube.com/watch?v=qCLmR9-YY7o
