The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides (mitosis, or M, stage)

1. subject: Human Genetics
By
Muhammad Jawad Ullah
Lecturer (MLT)
CUSIT

2. Meiosis
 Formation of Gametes (Eggs & Sperm)
 Called Reduction- division.
 Preceded by interphase which includes :
 chromosome replication
 Two meiotic divisions
 Meiosis I and Meiosis II
 Original cell is diploid (2n)
 Four daughter cells produced that are haploid (n)

3. MEIOSIS I: PROPHASE I
 Prophase I is further subdivided into periods known
as:
 Leptotena
 Zygotena
 Pachytena
 Diplotena
 Diakinesis

5. Metaphase-I
 Homologous pairs of chromosomes align along the
equator of the cell

6. Anaphase-I
 Homologs separate and move to opposite poles.
 Sister chromatids remain attached at their
centromeres.

7. Telophase-I
 Nuclear envelopes reassemble.
 Spindle disappears.
 Cytokinesis divides cell into two.

9. Prophase-II
 Nuclear envelope fragments.
 Spindle forms

10. Metaphase-II
 Chromosomes align along equator of cell.

11. Anaphase-II
 Sister chromatids:
 separates
 Move to opposite poles.

12. Telophase-II
 Nuclear envelope assembles.
 Chromosomes decondense.
 Spindle disappears.
 Cytokinesis divides cell
 Four haploid cells with one copy of each chromosome

14. Significance of meiosis
 Two haploid (1n) gametes are brought together
through fertilization to form a diploid (2n) zygote
 Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number.