1. Prophase Metaphase Anaphase Telephase Cellular Control Meiosis
Spindle fibers attach to the two sister chromatids of each chromosome contract and separate chromosomes which move to opposite poles of the cell.
Metaphase
Spindle apparatus attaches to sister chromatids of each chromosome. All the chromosomes are line up at the equator of the spindle
Anaphase
DNA and proteins start to condense. The two centrioles move toward the opposite end of the cell to form a spindle. The nuclear envelope and nucleolus also start to break up.
Telephase
the chromosomes become less condensed and reappear as chromatin. New membrane forms nuclear envelopes and the nucleolus is reformed.

2. Can you think of 3 reasons why mitosis is important?

3. Meiosis
Aims: Why is meiosis necessary? What happens during meiosis? How does meiosis create genetic variation?
Starter
Match up

4. Meiosis
Produces 4 daughter cells each with half the amount of DNA as the parent cell.
In sexual reproduction 2 gametes fuse to give rise to new offspring. This requires 2 haploid cells to join together to make 1 diploid cell.
In order to maintain a constant number of chromosomes in the adults of species, the number of chromosomes needs to be halved during meiosis.
SNA 14/12/04

5. Meiosis
Every diploid cell of an organism has 2 sets of chromosomes, one from each parent.
During meiosis, the homologous pairs of chromosomes separate, so that only one chromosome from each parent enters each gamete.
These are know as haploid cells.
SNA 14/12/04

6. Cellular Control
Meiosis 2n 2n
diploid 2n 2n 4n

7. Cellular Control
Meiosis 2n 2n
diploid 2n 1n 1n
haploid
haploid

8. only found in sexual reproduction
Meiosis
only found in sexual reproduction
produces haploid gametes
(egg/sperm, pollen/ovule)
takes place in the sex organs
(ovary/testes, stamens/carpel)
Introduces genetic variation

9. Meiosis - Involves 2 nuclear divisions
During interphase each chromosome replicates  each chromosome is made up of 2 chromatids
Meiosis I
Homologous chromosome form bivalents
Chiasmata form & crossing over occurs
Homologous chromosomes separate
Meiosis II
Chromatids separate

10. Significance of meiosis
Halves the diploid chromosome number
 haploid gametes
Diploid cells are formed on fertilisation
Increases variation
Independent segregation of maternal & paternal chromosomes
crossing over so that genes on the same chromosome are not always inherited together

12. Meiosis I Homologous chromosomes separate Interphase
Thread-like chromosomes
Chromosomes replicate (DNA synthesis)
Centrioles replicate

13. Prophase I
Chromatin condenses and coils  chromosomes become visible
Nuclear membrane breaks down & nucleolus disappears
Spindle starts to form
Homologous pairs of chromosomes form bivalents
Chiasmata form  crossing over
Homologous chromosomes repel but remain attached at chiasmata

14. Metaphase I
Bivalents line up along the equator
attached to the spindle by their centromeres
Anaphase I
Homologous chromosomes separate and are pulled by the spindle fibres towards opposite poles of the cell
Independent segregation (random separation of maternal & paternal chromosomes)

15. Chromosomes reach poles
Telophase I
Chromosomes reach poles
Often the cell goes straight into meiosis II
Spindle disappears
Nuclear membrane starts to reform
Cell divides by cytokinesis

16. Meiosis II chromatids separate
Prophase II
Spindle forms
(at right angles to original spindle)
(nuclear membrane disappears if it had reformed)

17. Metaphase II
Chromosomes line up at equator attached to spindle by their centromere
Anaphase II
Centomeres divide & chromatids separate

18. Telophase II Chromosomes reach poles & uncoil Spindle disappears
Nuclear membrane reforms
Cytoplasm divides (cytokinesis)
Tetrad of 4 haploid cells

20. see http://www. sumanasinc. com/webcontent/anisamples/biology/biology
For animation of meiosis

21. Role of chiasmata
Hold homologous chromosomes together as a bivalent
Separate alleles on same chromosome  increased genetic variation in gametes

22. Genetic Recombination
Cellular Control
Meiosis 2n
1 cell 2n
2 cell
replication
Prophase I
Prophase II 4n
1 cell
Genetic Recombination
Metaphase I
Metaphase II
Anaphase I
Anaphase II
Telephase I
Telephase II 2n
2 cell 1n
4 cell

24. Identify one difference between mitosis and Meiosis
Cellular Control
Cellular Control
Apoptosis
Identify one difference between mitosis and Meiosis

25. 2 Without genetic recombination:
Cellular Control
Meiosis
Without genetic recombination:
How many genetically different gametes could a human make?
23 Chromosomes
2 genetically distinct chromatids
Maternal stays with maternal
Paternal stay with paternal 2

26. gene for a characteristic gene for a characteristic
Cellular Control
Meiosis
gene for a characteristic
(protein)
gene for a characteristic
(protein)
Inherited from male
Inherited from female
Paternal Chromatid
Maternal Chromatid
Genes have a position on a chromosome (in a genome) that is conserved among species
LOCUS (loci)

27. Cellular Control Meiosis
Different versions of a gene, that code for different versions of a characteristic, are called alleles

28. Evolution via natural selection requires variation within a population
Cellular Control
Meiosis 2
Evolution via natural selection requires variation within a population

29. Cellular Control
Meiosis 4
Evolution via natural selection requires variation within a population
Sexual Reproduction
Combining gametes from 2 organisms doubles genetic variation

30. Cellular Control
Meiosis
529
Evolution via natural selection requires variation within a population
Sexual Reproduction
Combining gametes from 2 organisms doubles genetic variation
Independent assortment
Maternal and paternal chromatids distributed to gametes independently from each other (randomly)

31. Cellular Control
Meiosis 8
Evolution via natural selection requires variation within a population
Sexual Reproduction
Combining gametes from 2 organisms doubles genetic variation
Independent assortment
Maternal and paternal chromatids distributed to gametes independently from each other (randomly)
Crossing Over
Alleles on Chromatids are randomly distributed between sister chromatids

32. Cellular Control Cellular Control Apoptosis Homologous pairs
Chromatids
Loci
Alleles
Chiasmata
Crossing over

33. Errors in Meiosis Cellular Control Cellular Control Apoptosis
Multiple copies of genes leads to variability in gene expression and adaptability
Mutations
Polypoidy
Mutation rate of DNA is higher during meiosis and those mutations are passed on to offspring
Increases genetic variability in plants
Genetic Abnormalities in most animals
Multiple copies of genes leads to inbalance of gene products and abnormalities

34. Kleinfelter’s Syndrome
Cellular Control
Cellular Control
Apoptosis
Errors in Meiosis
Kleinfelter’s Syndrome
XXY, XXXY, XXXY
Sterile or low fertility
Hormonal imbalances
Learning difficulties
Increase risk of cancers
Polypoidy
Increases genetic variability in plants
Genetic Abnormalities in most animals
Multiple copies of genes leads to inbalance of gene products and abnormalities

35. Meiosis
Aims: Why is meiosis necessary? What happens during meiosis? How does meiosis create genetic variation?
Plenary
Match up

36. Cellular Control Meiosis Chiasmata Cytokinesis loci Homologous pairs
Crossing over
Centrioles
Gametes
Chromatid
Chromatin
Spindle fibres
Centromeres