Cell division and Genetic Stuff


DNA and Genes

  • 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
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Unique DNA

  • 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.
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What is Mitosis for?

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

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What is Mitosis?

  • 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.
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Diagram for Mitosis

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Gamete have half the usual number of chromosomes

  • 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).

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What is meiosis?

  • 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.
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Diagram for Meiosis

Stem Cell- Embryonic

  • Embryonic stem cells can turn into any type of cell
  • This happens by a process called differentiation which is where a cell changes to become specialliased for its job.
  • In most animal cells, the ability to differentiate is lost at an early stage, but lots of plant cells don't lose this ability.
  • Stems cells are found in early human embryos.
  • Adults have stem cells, but they're only found in certain paces. like bone marrow. These aren't as versatile as embryonic stem cells- they can't turn into any cell type at all, only certain ones.
  • Embryonic stem cells could be used to replace faulty cells in sick people- you could make a beating heart muscle cells for people with heart disease, insulin- producing cells for people with diabetes or nerve cells for people paralysed by spinal injuries.
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Genetic Disorders

Cysic Fibrosis- is a genetic disorder of the cell membranes, it results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas.

  •  The allele which cause cysic fibrosis is a recessive allele, 'f'
  • Because it is recessice, people with only one copy of the allele won't have the disorder- these people are known as carriers
  • For a child to have the disorder, both of the parents must be either carriers or sufferers.

Polydactyly- is a genetic disorder where a baby is born with extra fingers or toes

  • This disorder is caused by a dominate allele, 'D' and so it can be inherited if just one parent carries the defective allele
  • The parent that has teh defective allele will be a suferer too since the allele is dominant.
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