Cell division and Genetic Stuff

• Strands of Deoxyribonucleic Acid
• Contains all of the instructions to put organism together and make it work
• Found in the nucleus of plant and animal cells, in long molecules called Chromosomes

A gene codes for a specific protein:

• Genes is a section of DNA, they contain instructions to make a specific protein
• Cells make proteins by string amino acids together
• Only 20 amino acids are used to make 1000's of proteins
• DNA determines what proteins the cell produces
  

• Everyone has unique DNA, expept identical twins
• DNA fingerprinting is a way of cutting up a persons DNA into small sections and then separating them.  Each person's genetic fingerprint has a unique pattern. This means you can tell people apart by comparing samples of their DNA.

DNA fingerprinting is used in...

• Forensic science- DNA taken from a crime scene is compared with DNA from a suspect.
• Paternity testing- to see if a man is the father of a particular child.
  

Mitosis makes new cells for growth and repair

• Body cells normally have 2 copies of each chromosomes- one pair from the mother and one pair from the father.
• This diagram shows the 23 pairs of chromosomes from a human cell.
• When a body cell divides it need to make new cells identical to teh original cell- same number of chromosomes

• 1. Before the cell begins to divide the DNA is spread out in long strings
• 2. Once the cell 'gets the signal' to divide it duplicates the DNA
• 3. The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The 2 arms of each chromosome go to the opposite end of the cell
• 4. Membranes then form around each of the sets of chromosomes. These become the nuclei of teh two new cells.
• 5. Lastly, the cytoplasm divides
• 6. you then have two new cells containing the exact same DNA as their pairent cell had, they are identical.

• During sexual reproduction, two cells called gametes  combine to form a new individual.
• Gametes only have one copy of each chromosomes, this is so when you combine a 'mother' and 'father' cell it ends up with the right number of chromosomes in body cells
• The new individual will have a mixture of two sets of chromosomes, so it will inherit features from both parents. This is how sexual reproduction produces variations.

Meiosis involves two divisions:

To make two new cells which only have half the original number of chromosomes, cells divide by meiosis. In humans, it only happens in teh reproductive organs (e.g. ovaries or testes).

• 1. Before the cell starts to divide, it duplicates its DNA- one arm of each chromosome is an exact copy of teh other arm.
• 2. In the first division, the pairs line up in the centre of the cell.
• 3. The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some of the fathers and some of the mothers chromosomes go into the new cell.
• 4. In the second division, the chromosomes line up again in the centre of the cell. Then the arms are pulled apart, like mitosis.
• 5. This results in 4 new gametes with only a single set of chromosomes in it.