3D easy to understand animation on the stages of Mitosis

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html beast animation on mitosis

3.24c mitosis

Key points:
The nucleus of the cell contains chromosomes. During the resting stage of the cell cycle known as the interphase, the chromosomes undergo a process called DNA replication. This creates two copies of each chromosomes which are held together by a structure called the central mere.

Normally, you would see the nucleus as a spherical structure and you would not be able to see any chromosomes. The first sign that a cell is going into mitosis is when you see the nucleus membrane breaking down. Called pro phase. Then the chromosomes become visible. Visible as a pair of Chromatids. Each chromosome has been copied, held together by central mere. The cell division continues, inside the cell a network of protein molecules, spindle and the spindle fibres, extend from one pole of the cell to the other. Late pro phase, chromosome pair will move towards the spindle and will join to one spindle fibre at the central mere. Next stage, metaphase. To show it easily, its only showing one pair of chromatids. The pair of chromatids join on the spindle fibre at the equator, or middle of the fibre. The next phase is known as the Anaphase. In the anaphase, the spindle fibre shortens and pulls the chomatids in opposing direction. They separate and move to the poles of the cell. The end of mitosis is shown by telophase, in which the nucleus begins to reform around the chromosomes which have been pulled to the poles of the cell. So in the telophase we see the formation of 2 nuclei at opposite ends of the cell. Finally, a phase known as cytokinesis, the cell splits into two. This is NOT part of mitosis. The cell divides itself, and the membrane will fuse across the middle. They each contain a chromosome which is the same as the parental chromosome. Basically, both cells each contain the same amount of chromosomes as the parent cell, eg. if the parent cell had 23 chromosomes, then both of the cells created would EACH have 23 chromosomes.

3.24 b Mitosis

Key Points:
1. Covering the basics, mitosis is the process in which a cell divides into two cells, which have identical properties such as sets of chromosomes.
2. This requires that the first cell has to copy its chromosomes. This process is known as DNA replication. In the process, each chromosome undergoes a copy process to produce a replica of it with the same genes and alleles and they are held together by a structure called the central mere.
3. While the chromosomes are held together, they are referred to as a pair of chromatids.
4. The process of DNA replication takes place inside the nucleus, while its still intact. Its not visible. This is known as the inter phase.

3.24 a Mitosis

Key points:
1. Mitosis is a form of cell division which results in growth. Increase in number of cells.
2. A normal cell has a nucleus, and the number of chromosomes in there is known as the diploid number, or substituted as 2n. For humans, 2n = 46, for cats 2n = 38.
3. During mitosis, a cell will divide into two cells, each with a nucleus. Inside the nucleus of each one you'll find it has a diploid nucleus. These cells are identical, or daughter cells. They are identical in 2 ways. They have the same number of chromosomes, and the second is that they have the same set of chromosomes.
4. This means that one chromosome in one cell is identical to the same version on it in the other cell.

How are the copies of chromosomes made?
How do they separate?
For the answers, look to the blog posts above.

Key Points:
1. The chromosome on the left is likely to contain thousands of genes. Selecting one area of this chromosome, called the gene loci, and zooming in will show the individual strands of DNA. What you see is a double helix shape. They appear to be parallel.
2. By zooming in again, you will be able to see what's holding the two strands together. The sections on the diagram on the right are known as the sugar-phosphate backbone. In the centre there are a group of molecules called bases.
3. There are 4 different types of bases. Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
4. These bases are holding together the two helix's and they're held together by A-T and G-C bonds. These are known as the base pairs. This is always found in DNA. They glue one side of the double helix to the other.
5. The order on the right side is A-C-T-G-A-A-C-C-A-G. Order of the bases. It's this order that we call the gene. The gene is inside the nucleus. Gene - Order of bases and number of bases ---> Protein in cytoplasm. And in the end this gives the characteristic. The gene is the order of the bases on one side of the double helix.

3.15 Genes

Key Points:
1. A gene is a section of a molecule of DNA.
2. Once again the double helix shape is shown. A section of the DNA is called a gene. This gene carries the information which forms the characteristic of the organism, eg. Blood group, petal colour..
3. The genes are all located in the nucleus, and the information is passed to the cytoplasm and then it gets transformed into a protein and its this protein which controls the production of the characteristic.

This is a strand of DNA, each section is called a gene. As you can see, DNA has a double helix shape because of the homologous pairing.

3.14 Chromosomes

Key Points:
1. The nucleus of a cell contains genes, and the genes are located in the chromosomes.
2. Chromosomes are the genetic information within a cell. In a normal cell, the nucleus would contain a number of chromosomes.
3. The photograph shows a single human chromosome. The chromosome is composed of DNA, which stands for Deoxyribonucleic acid, and this forms a shape known as the double helix. 
4. Sections of this molecule are called genes, one chromosome will have many genes eg. 1000
5. Each gene carries the information for the construction of a protein. The protein has a characteristic associated with the gene, eg. Blood group. 
6. Different organisms have different numbers of chromosomes. Cats have 38, Chickens have 78, and Humans have 46 chromosomes per cell.
7.  Chromosomes operate in pairs, homologous pairs. The next diagram shows the homologous pairs. The homologous nature is based on the length of the chromosomes. A gene located on a chromosome is called the gene loci. If you go to the same position on the other gene in the homologous pair, the same gene will be there. Basically 2 versions of each gene for one characteristic. These versions are called alleles.

3.1 Sexual and Asexual reproduction

1. Organisms that show sexual production show genders, male and female
2. This doesn't occur in asexual reproduction
3. Organisms that show sexual reproduction produce cells gametes, in the male this is a sperm cell and in the female it is the egg. In plants the sperm cell is known as the pollen, and the egg is the ovule.
4. Asexual populations produce no gametes
5. The type of cell divisions that produce gametes is called meiosis. One of its effects is to half the total adult number of chromosomes in the gamete cell
6. In humans the total number of chromosomes in an adult is 46 per cell, however there are only 23 per gamete cell. The process in which is halves is called meiosis
7. In asexual reproduction there is no meiosis, there is mitosis and binary fission in procariotic bacterial cells. The number of chromosomes is maintained constantly. A cell with 20 chromosomes would divide into 2 cells, both with 20 chromosomes. These 2 cells are identical.
8. In sexually reproducing populations there is the process of fertilisation. This is where the sperm cell of a male and the egg cell of the female fuse together.
9. In asexually reproducing organisms there is no fertilisation.
10. In sexually reproducing organisms, there are variations, and these variations are broad. There are many differences. In asexually reproducing organisms, there is small variation and very little differences but in large, they are identical.

Question: When the amount of chromosomes is halved, are they randomly picked or are there specific types of chromosomes that are needed?

This is an example of a sexually reproducing organism

Mushrooms are an example of asexually reproducing organisms