mitosis and meiosis
Nuclear division can take place by either mitosis or meiosis:
Mitosis produces two daughter nuclei that have the same number of chromosomes as the parent cell and each other. Mitosis is the division of the nucleus of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell
Meiosis produces four daughter nuclei, each with half the number of chromosomes as the parent cell
So what is Mitosis??
And what is meiosis??
mitosis - a process of nuclear division
- produces two daughter nuclei that have the same number of chromosomes as each other and the parent cell
meiosis - a process of nuclear division
- produces four daughter nuclei
- each daughter nuclei has half the number of chromosomes that the parent cell
Except rare event of mutation, the gentic make up of the two daughter nuclei is identical to that of the parent nucleus as well as being an exact copy of the parent cell.
Mitosis is always preceeded by a period during which the cell is not dividing. This period is called interphase. Interphase is a period of considerable cellular activity that includes a very important event, the replication of DNA.
1) In what circumstances may the genetic make-up of the daughter cells and nucleus NOT be identical to the parent cell/nucleus??
2) what is mitosis always preceeded by??
3) What is interphase??
3) a period of considerable cellular activity that includes the important replication of DNA
Although mitosis is a continuous process, it can be divided into four stages:
1) PROPHASE - the chromosomes become visible and the nuclear envelope dissapears
2) METAPHASE - the chromosomes arrange themselves at the centre (equator) of the cell
3) ANAPHASE - each of the two threads of a chromosome (chromatid) migrates to an opposite pole
4) TELOPHASE - the nuclear envelope reforms
So what are the four stages of mitosis??
Prophase - chromosomes become visible
- nuclear envelope disintegrates
- nucleolus dissapears
Metaphase - spindle forms
- chromosomes line up on equator of cell
Anaphase - spindle fibres attached to chromatids contract
- chromatids are pulled towards poles
Telophase - chromatids reach poles and become indistinct
- nuclear envelope reforms
- nucleolus reforms
- spindle disintegrates
(Interphase) - cell is actively synthesising proteins
- chromosomes invisible
- prior to mitosis, DNA replicates
mitosis is important in organisms because it produces daughter cells that are genetically identical to the parent cells.
there are three main reasons why this is so essential:
- Growth - when 2 haploid cells (e.g sperm and ovum) fuse together to form a diploid cell, this diploid cell has all the gentic information needed to form the new organism. if the new organism is to resemble its parents, all the cells that grow from this original cell must possess this same set of genetic information. mitosis ensures that this happens.
- Differentiation - these cells differentiate, to give groups of specialised cells, e.g. epithelium in animals or xylem in plants. these different cell types each divide by mitosis to give tissues made up of identical cells which perform a particular function.the tissue can only function effectively if all its cells have the same structure and perform the same function
- Repair - if the cells are damaged or die it is important that the new cells produced have an identical structure and functin to the ones that have been lost. if they were not exact copies the tissue would not function as it did before.
SO WHAT ARE THE THREE MAIN REASONS WHY MITOSIS IS
Growth- all the cells that grow from their original cell must possess the same set of genetic info. as the original cell. mitosis ensures this
Differentiation - groups of specialised cells need to divide by mitosis to give tissues made up of identical cells which perform the same particular function
Repair - when cells get damaged or die it is important that new cells have an identical structure and function to the ones that are lost.