Cell division Part 3
Nucleus is starting to surround the chromosomes on both sides. The full process of mitosis cell division is known as karyokinesis. Now remember cytoplasm? It surrounds only one nucleus. So, after mitosis stages, when there are two nucleus, it also has to separate into two. The process cytokinesis is responsible for the final septation into two cells by splitting the cytoplasm.
There are some human cells that don't have 46 chromosomes. Human sperm cells and egg cells which are also known as gametes have 23 chromosomes when a sperm cell and an egg cell come together that makes 46 chromosomes. That will allow a newly formed fertilized egg to develop into a human. Meiosis is a reduction division because you have a starting cell that has 46 chromosomes and your ending cells-the sperm and egg cell have only 23 chromosomes. Just like mitosis, interphase occurs before meiosis takes place. In meiosis, similar stages occur but they occur twice. First occurrence can be stated as meiosis 1 and the second one can be called meiosis 2.
Prophase 1 is where the chromosomes are going to condense and thicken and they're going to line up with their homologous pairs. In meiosis an amazing process occurs called crossing over. The original and duplicated chromosome (as they're united with centromere) pairs with their homologous pairs which is called crossing over. This is how 4 chromatids make a single pair. then like mitosis in metaphase stage chromosomes line up in the middle of the cell but this time there are 2 pairs of chromosomes together in every line. Similarly in anaphase these homologous pairs are Carried away and in telophase they're divided into two cells including cytoplasm. After completing meiosis 1, there are 2 cells and each cell has 23 chromosomes but 46 chromatids as as the pairs have separated.Then, just like the mitosis process, In meiosis 2, these two cells containing 23 chromosomes, again divide into 2 cells. Each of the last two cells contain 23 chromosomes but each chromosome is of a single chromatid in other word, each cell consists of 23 chromatids.
