This is the reason meiosis is also known as a reduction division process. Thus, in meiosis germ cells are divided by two fissions of the nucleus which result in four gametes or sex cells. Each cell possesses half the number of chromosomes of the parent cell. The process of meiosis occurs …show more content…
As there are two divisions in meiosis, the two divisions are called meiosis I where the cell divides for the first time and meiosis II where the cell divides for the second time.
Meiosis starts with duplication of chromosomes. Then the parent cell undergoes two rounds of nuclear divisions (meiosis I and meiosis II). Thus in an overall meiosis process, four daughter cells are produced from the parent cell. However, before entering the stages of meiosis the parent cell go through a phase called interphase. Similar to mitosis, the cells growth begins in the G1 phase of interphase, the chromosomes are duplicated in the S phase and then in G2 phase the parent cells prepares for cell division.
Before the start of meiosis I, the chromosomes are duplicated and they are fused together. The duplicated chromosomes are called sister chromatids. The point at which the duplicated chromosomes (sister chromatids) are joined is called centromere and the complete structure looks like a “letter X”. The chromosomes condense and become compact at the time of every nuclear division. At this point, they are visible under the microscope.
Meiosis …show more content…
Thus by the end of meiosis II, the chromosome number of cells that are undergoing the meiosis II process and in the resultant daughter cells remain unchanged. There are four stages of meiosis II.
After meiosis I, there are two cells with the same number of chromosomes or the same number of chromatid pairs. The chromosomes in each daughter cell once again condense into visible X shaped structure. The nuclear membrane around the nucleus of the daughter cells disintegrates releasing the chromosome. The meiotic spindles start forming again and the centrioles duplicate.
Metaphase II- The pair of sister chromatids arrange themselves in line along the equator of the cell. The centrioles are now present at the opposite ends in each of the daughter cells. The developed meiotic spindle fibers at each end attach onto the centromere present in the sister chromatids of the cell.
The meiotic spindle fibers start contracting and the sister chromatids are pulled to the opposite ends. At this point, the chromatids are separated and they form individual chromosomes.