3.24c

• the first sign of the chromosomes splitting is when we see the nuclear membrane start to break down' and the chromosomes become visible as a pair of chromotids
•this is known as 'prophase'
• with the nucleus gone a network of protein molecules called 'spindle' which extend from one pole of the cell to the other
• what happens is the chromotids connect to one of the spindles called 'metaphase'
• the chromosomes are in the middle of the cell (at the equator)
• anaphase - the fibre shortens pulling one chromotip in one direction and the other one in the opposite direction and the pair separates and move towards the poles of the cell
• telophase - the nucleus begins to reform at either end, creating two new cells
• cytokinesis - the cell finally splits into two (NOT REGARDED AS PART OF MITOSIS) now both cells include one chromosome.
• in human cells we see 23 cells cells seperating instead of two

3.24b

details of mitosis
• copying chromosomes is called TNA replication.
• here each chromosome undergoes a copying process to produce an identical copy of itself
• these two copies are held together by the centromere.
• we refer to the the pair as a 'pair of chromatids'
• there is also a process called interphase (that we cannot see) that separates the pair

3.24a

outline of the process of mitosis:
- the number of chromosomes in the cells nucleus is known as the 'diploid' number (abbreviated 2n)
for humans 2n = 46
for cats 2n = 38

• mitosis will make the cell divide in two, each with it's own nucleus. these cells are described as identical, daughter cells
• each of these cells has a diploid nucleus
• the cells have the same number of chromosomes as well as the same set of chromosomes
• this means that if we take a chromosome from either cell and you will find an identical chromosome

how are the copies of chromosomes made? and how to they separate?

3.16

• 1 chromosome = 1000 genes
• if you magnify 1 gene loci you find a double helix (genes are parallel)

• when magnifying it even more you can see that there is what we call a base holding them together
• four different base types: Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
• base types are always found in pairs T-A G-C T-G
• one side of the chromosomes has a ACTGAACCAG order to the bases which we call a gene

3.15

3.14

• chromosome - the genetic data inside a cell which is in the nucleus (brain) of the cell
• chromosomes are made up of DNA molecules which come in a helix shape
• a section of DNA is called genes
• depending on what kind of organism you are, the chromosome count in your body will be different
• chromosomes function in (homologous) pairs, which means that if you took a gene on one chromosome (called gene loci), and when you would go to the corresponding gene on the opposite chromosome, it would be the same gene
• therefore we have 2 versions of each gene, called alleles

3.1 sexual and asexual reproduction

• Organisms that show sexual reproduction show sexes (male/female). No sexes exist in Asexual reproduction.
• Sexual reproduction has Gameke cells in the sperm and egg cells. Asexual does not have Gameke cells.
• Meiosis is a cell division that produces Gamekes. One of Meiosis' effects is to half the number of chromosomes in the Gameke cell. 
•  Total number of chromosomes in a human is 46 per cell. In Gamekes the total number is 23 per Gameke cell. From 46 to 23 is the process of Meiosis.
• In Asexual reproduction there is Mitosis and Binary fission bacterial cells. Number of chromosomes is maintained constantly.
• In Sexual reproduction there is the process of fertilisation, where the sperm cell and egg cell fuse together. In Asexual reproduction there is no fertilisation and no fusion of cells.
• Many differences in the individuals of a sexual reproducing population. Where as Asexual show a small amount of variation, mainly identical (clone).  

credit to samir