Mitosis and Meiosis Important Points to know
Mitosis: mitosis is cellular division that occurs during times of growth, tissue repair, asexual
reproduction, it is also seen in many pathologies of human illness. Cancer is uncontrolled cellular
growth.
Mitosis occurs in the somatic (soma=body ) cells. These are all the cells other than sex cells. So they are
the skin cells, cells lining body cavities, your pancreas cells, retinal cells, all cells of the body except sex
cells. Mitosis results in two new daughter cells that are identical with respect to the parent cell with
regards to chromosome number. So In other words, if a cell has say 46 chromosomes and undergoes
the process of mitosis each new daughter cell with have 46 chromosomes as well. There is one DNA
replication and one cellular division.
Stages of mitosis:
Interphase- this is the stage at which cells spent most of their time in the cell cycle. At some point the
DNA may get replicated; it happens in the S phase (S=synthesis) of Interphase.
Prophase- stage at which the chromosomes are visible, they have condensed.
Metaphase- chromosomes lineup at the equator of the cell.
Anaphase- duplicated chromosomes separate at the centromere and begin their travel to opposite
poles
Telophase- chromosomes have traveled to opposite poles and cell has begun to pinch off or form two
new cells. New nuclear membranes have formed.
The actual pinching off process resulting in two new cell sis called cytokinesis.
Meiosis: the purpose of meiosis is to produce sexual cells, eggs or sperm used in sexual reproduction.
Meiosis occurs in the testes for males and the ovaries in females . Sexual reproduction involves uniting
a sperm that is haploid (unpaired chromosomes) with a haploid egg. The result is a diploid cell called a
zygote, that is then capable of developing via mitosis into an embryo.
The bottom line is that the cells produced possess half the chromosomes of the original parent cell.
Meiosis occurs in diploid organisms (diploid means paired chromosomes). The homologous pairs are
what’s being separated here. What is a homologous pair? It is a pair of chromosomes that have the
same genes in the same location. One chromosome you get from your mother the other in the pair you
received from your father. Humans have 23 paired chromosomes ; 46 total.
The stages of meiosis are similar to mitosis. To reduce the chromosomes number by half the DNA is
replicated once just like in mitosis but there are two cellular division.
Meiosis I: DNA is replicated but at metaphase 1 the homologous pairs line up opposite each other at
the cellular equator. During anaphase 1 the homologous pairs separate.
At the end of telophase 1 the cells are now haploid since the pairs have separated. Even though the
duplicated chromosomes (called sister chromatids) are still attached at the centromere.
Meiosis 2. Is virtually identical to mitosis, here the chromosomes line up at the equator in meiosis 2 and
the sister chromatids separate at anaphase 2. At telophase 2 the new nuclear membranes are formed
and new daughter cells are created.
In the above example the cells are diploid, containing 4 chromosomes, 2 homologous pairs. At the end
of meiosis 1 there are two new cells that are haploid but still have their duplicated chromosomes (sister
chromatids). Each of these cells then undergoes meiosis 2 and the result is 4 total cells that have exactly
half the number of chromosomes as the original parent. It is important to point out that each new sex
cell has one of each chromosome of the original pairs.