1. Most images/information from click4biology.com
4.2 Meiosis
Most images/information from click4biology.com

2. Meiosis
Is a relatively rare type of cell division that produces haploid gamete cells (sperm, pollen nuclei, ovules and eggs). Meiosis can be view as two consecutive rounds of cell division:
Meiosis 1 separates the homologous pairs of chromosomes
2) Meiosis 2 separates the sister chromatids.

3. Meiosis is a reduction division of a diploid nucleus(2n) to form a haploid nucleus (n).

4. Meiosis is a reduction division of a diploid nucleus(2n) to form a haploid nucleus (n).
(a) The cell is in G1 of the interphase and has a total of 2 chromosomes, 2n=2.

5. (b) The S phase of the interphase is DNA replication.
Meiosis is a reduction division of a diploid nucleus(2n) to form a haploid nucleus (n).
(a) The cell is in G1 of the interphase and has a total of 2 chromosomes, 2n=2.
(b) The S phase of the interphase is DNA replication.

6. (b) The S phase of the interphase is DNA replication.
Meiosis is a reduction division of a diploid nucleus(2n) to form a haploid nucleus (n).
(a) The cell is in G1 of the interphase and has a total of 2 chromosomes, 2n=2.
(b) The S phase of the interphase is DNA replication.
(c) In G2 of the interphase the cell has two daughter chromatids per chromosome, the cell mass of DNA has doubled.

7. (e) The diploid cell has divided to form haploid gamete cells (n=1).
Meiosis is a reduction division of a diploid nucleus(2n) to form a haploid nucleus (n).
(d) Meiosis occurs in a series of phases similar to mitosis but with significant differences.
(e) The diploid cell has divided to form haploid gamete cells (n=1).
(f) The homologous pair of chromosomes has been separated (red from blue).
***One diploid cell which undergoes meiosis produces four haploid gametic cells.***

8. HOMOLOGOUS CHROMOSOMES

9. HOMOLOGOUS CHROMOSOMES
Homologous chromosomes form
pairs within the nucleus and during cell division.

10. HOMOLOGOUS CHROMOSOMES
Homologous chromosomes form
pairs within the nucleus and during cell division.
The name suggest that both members of the pair share
certain structural characteristics. Such as…
same length.
same shape.
same genes in the same gene loci.
**Note that for every gene there are normally two alleles in the individual.

12. MEIOSIS FACTs Type of cell division Produces gametes
Takes place in the reproductive organs ONLY
Time?....varies
Produces millions of gametes in short amount of time
Still considered rare
AAAAqQ/euHqORTen7o/P Sperm_cell,_SEM-SPL.jpg

13. FOR THE FOLLOWING EXAMPLE
The stages of meiosis will be shown but first we will begin with some diagrams about Interphase as a reminder.
In the diagrams homologous pairs are shown in different colors
((red with blue)
((purple with green))
The organism shown is an animal cell with a diploid number (2n)= 4.
Therefore we expect to see four gametes each with a haploid number _____?

14. FOR THE FOLLOWING EXAMPLE
The stages of meiosis will be shown but first we will begin with some diagrams about Interphase as a reminder.
In the diagrams homologous pairs are shown in different colors
((red with blue)
((purple with green))
The organism shown is an animal cell with a diploid number (2n)= 4.
Therefore we expect to see four gametes each with a haploid number n = 2

15. -first of two sets of divisions. -PMAT will divide the cell into two
Meiosis I: 
-first of two sets of divisions.
-PMAT will divide the cell into two
-separate the homologous pairs.
This is perhaps the most significant
step in terms of genetics.

17. chromosome homologous pair duplicated

18. Early G1
Late G1
S phase

19. Early prophase
Spindle fiber attachment
Migrate towards middle

20. ALL sister chromatids at middle of cell.
CROSSING OVER

21. *Occurs during P but most visible in M
Crossing Over: the exchange of genetic material between non-sister chromatids
*Occurs during P but most visible in M
The point at which the chromosomes exchange genetic information is called the chiasma.

22. HOW MANY CHIASMA ARE THERE???

23. HOW MANY CHIASMA ARE THERE???

24. Early anaphase
spindle fibers contract
Late anaphase
sister chromatids pulled to opposite poles

25. -Chromosomes are now in two sets at
opposite ends of the cell.
Each set contains one from each of the homologous pairs.
In some species a nuclear membrane may form, in
others there is a progression straight into Prophase II.
End of mitosis I

26. -involves the separation of the sister chromatids
Meiosis II:
-involves the separation of the sister chromatids
-looks very like mitosis.

31. TETRAD of haploid cells

32. MEIOSIS
VIDEO

33. http://sciencevideos. wordpress

34. NONDISJUNCTION

35. http://sciencevideos. wordpress

36. http://sciencevideos. wordpress

37. NONDISJUNCTION VIDEO

38. -result of non-disjunction - 3 copies of the same chromosome
TRISOMY
-result of non-disjunction
- 3 copies of the same chromosome

39. Individuals can experience learning and
TRISOMY 21
down syndrome
Individuals can experience learning and
social problems along with additional physiological
abnormalities.
Symptoms vary…

40. in karyotyping, chromosomes are
arranged in pairs according to their size and structure.

41. -Pictures can be taken of the human chromosomes during the metaphase.
-arranged into pairs on the basis of size and structure.