1. Meiosis:

2. Most reproduction occurs through sexual reproduction
Most reproduction occurs through sexual reproduction. Sexual reproduction is the recombination or mixture of genes. This results in the offspring having a combination of DNA from both parents. This will help add to:
(l) the variation within a population or a species.
(2)this also creates unique individuals, which are not identical to the parents.

3. Each species has a different number of chromosomes
Each species has a different number of chromosomes. For example, humans have 46 chromosomes (23pairs) in every body cell. All cells contain two complete sets of chromosomes( in humans each set has 23 making a total of 46) called the diploid (2n) number of chromosomes. The exception to this is with sex cells, such as egg and sperm. Since these will later combine they each only have one set of chromosomes , called haploid
(n) cells, and in humans this means they have 23 chromosomes total.

4. Meiosis is the formation of gametes, performed by reproductive cells only. This will result in a reduction of the chromosomes number, forming haploid cells meiosis produced 4 daughter cells, each with half the number of chromosomes, that are not identical to each other. This is again important because it, keeps the chromosome number constant over generations, in the adult organism. When the egg (n) and the sperm (n) combine (n + n) in fertilization, the offspring is a diploid cell (2n)

5. when chromosomes pair, in preparation for meiosis, they arrange with their homologous pair, otherwise known as homologs. This means that like chromosomes pair with each other

6. The homologous Pairs of chromosomes ate separated and end up in
4 daughter cells. This happens in two main states, meiosis I and meiosis II. The Pairs separate during meiosis I, and meiosis II is when the sister chromatids
separate, much like in mitosis.

7. Meiosis I is a 4 step process
Meiosis I is a 4 step process. The start of this is much like mitosis, the cells have gone through the G1, S and G2 phases, thus the DNA has been replicated and are in the form of sister chromatids, connected at the centromere. The main difference here is that the homologous pairs of chromosomes pair up and then proceed as follows .

8. Prophase I
is traditionally divided into five sequential
stages: leptotene, zygotene, pachytene, diplotene, and diakinesis
Leptotene. Chromosomes condense tightly.

9. Zygotene. Pairing of homologous chromosomes
Zygotene. Pairing of homologous chromosomes. This is accomplished with the help of the synaptonemal complex'' the synaptonemal complex pulls together homologous regions of the DNA. While not identical, homologous regions have a very high similarity

10. (Synapsis The sites the homologues attach to are adjacent, so that the
members of each homologous pair of chromosomes are brought close together. They then line up side by side, apparently guided by heterochromatin sequences, in the process called synapsis.)

11. Pachytene. Pachytene begins when synapsis is complete The synaptonemal complex thus provides the structural framework that enables crossing over between the homologous chromosomes.

12. Crossing Over: Within the synaptonemal complex, recombination is thought to be carried out during pachytene. The details of the crossing over process are not well understood, but involve a complex series of events in which DNA segments are exchanged between nonsister or sister chromatids. In humans, an average of two or three such crossover events occur per chromosome pair.

14. Chiasma Evidence of crossing over can often be seen under the light microscope as an X-shaped structure known as a chiasma . The presence of a chiasma indicates that two chromatids (one from each homologue) have exchanged parts . the chiasmata move to the end of the chromosome arm as the homologous chromosomes separate.

16. Diplotene. At the beginning of diplotene, the protein lattice of the synaptonemal complex disassembles. Diplotene is a period of intense
cell growth. During this period the chromosomes decondense and become very active in transcription.

17. Diakinesis. At the beginning of diakinesis, the transition into metaphase, transcription ceases
and the chromosomes recondense.

19. Metaphase I
Each joined pair of homologues then lines up on the metaphase plate. The orientation of each pair on the spindle axis is random: either the maternal or the paternal homologue may orient toward a given pole.

20. Anaphase I(The first division is called the Reductional Division, since it is at this time that the chromosome count is reduced to one half In anaphase I
Because the microtubules are attached to kinetochores on only one side of each centromere, the individual centromeres are not pulled apart to form two daughter centromeres, as they are in mitosis. Instead, the entire centromere moves to one pole, taking both sister chromatids with it

21. When the spindle fibers have fully contracted, each pole has a complete haploid set of chromosomes consisting of one member of each homologous pair meiosis I results in the independent assortment of maternal and paternal chromosomes into the gametes.

22. Telophase I
By the beginning of telophase I, the chromosomes have segregated into two clusters, one at each pole of the cell. Now the nuclear membrane re-forms around each daughter nucleus. Cytokinesis may or may not occur after telophase I. The second meiotic division, meiosis II, occurs
after an interval of variable length.

23. The Second Meiotic Division
After a typically brief interphase, in which no DNA synthesis occurs, the second meiotic division begins. Meiosis II resembles a normal mitotic division. Prophase II, metaphase II, anaphase II, and telophase II follow in
quick succession

24. In female , during the meiotic cell division of female germ cells, unequal division of the cytoplasm occurs which leads to the formation of :-
One primary Oocyte.
Three small polar bodies which will degenerate.
The primary Oocyte are formed early during the embryonic development of female fetus. They remain in the prophase stage of the first meiotic cell division for years until puberty is reached, then the first meiotic cell division is completed.

26. End