Genetics

This is the study of how characteristics are passed on from one generation to the next.
1. The raw material for genetics is genetic variation.
  1. No two organisms of the same species are identical (except identical twins).
Genetic Variation:
1. is that variation that can be passed on from one generation og organisms to the next = INHERITED.
2. Genetic variation is not to be confused with that vaiation that is caused by the environment which is not inherited. E.g a muscle builder does not pass on his big muscles to his offspring. = ENVIRONMENTAL
3. : Genetic Variation can be divided into two sorts.
  1. CONTINUOUS: where a characteristic can take a range of values e.g foot length, lung volume.
  2. DISCONTINUOUS or DISCRETE: all or nothing, this characteristic is either there or not there e.g fixed or free earlobes. There is no range.
4. Variation means having different genes in a population. This variation can be inheritable (passed on from generation to generation e.g height) or envionmental e.g tanned skin. Variation increases a species chance of survival in changing environments, because certain traits are better suited to certain conditions than others. This means that species with more variation have a greater chance of surviving change than those with little/no variation.
Structure of DNA:
1. DNA is found in the nucleus of cells.
2. STRUCTURE: DNA is a molecule shaped like a twisted ladder - known as a double helix.
  1. The backbone of the "ladder" is made up of a phosphate group and a sugar (deoxyribose).
    1. The 'rungs' of the ladder are made of base pairs.
3. Nucleotide:
DNA Replication:
1. When an organism grows, repairs itself, reproduces or replaces old cells, new cells need to be made. Every new cell needs it's own copy of the genetic code (DNA) that is the same as the original. It is making these new copies of DNA that is called DNA replication.
  1. Each newly formed double helix is made up of one original (parent) strand and one newly made daughter strand.
    1. This is known as semi - conservative replication (semi = half, conservative - to keep the same) .
2. The DNA Replication Process: 1. The DNA double helix unwinds and the two strands are seperated.
  1. 2. The original strands of DNA act as templates to make new strands that match.
    1. 3. There are now two identical DNA molecules that wind up seperately and each will go into a new cell.
3. PROCESS:
  1. 1. Hydrogen bonds are broken between base pairs:
    1. 2. DNA molecule unwinds and unzips:
      1. 3. New molecule nucleotides pair up:
        4. Bonds reform and DNA molecule winds up.
Cell Division:
1. Cells often need to be replaced - because theyve grown old or died. New cells are made by a from of celld divison called MITOSIS.
  1. This process happens in all of your cells, apart from the testes and ovaries.
  2. It creates 2 cells, both individual to the original, mother cell.
    1. This process is completed in a series of steps:
      1. The chromosomes condense (become shorter and fatter).
      2. The chromosomes replicate.
      3. The chromosomes line up singularly along the middle.
2. MITOSIS - the splitting of the replicated chromosomes.
3. MEIOSIS:
  1. This is the form of cell division that is used to create sex cells (egg and sperm) in the gametes (testes and ovaries in animals).
  2. Meiosis creates 4 daughter cells, each with 1/2 the number of chromosomes as the mother cell. This is because at fertilisation, 2 gametes will come together to create a new cell (zygote) which has the full number of chromosomes.
  3. PROCESS:
    1. Meiosis begins with a single cell. 1. Chromosomes condense and DNA is replicated
      1. 2. The homologous chromosomes line up along the equator in pairs. Non- sister chromatids exchange segmets = crossing over.
        3. The homologous chromosomes are pulled apart and the cell divides .. 2 cells.
        4. The chromosomes line up individually along the equator and the chromatids are seperated.
        5. The 2 cells divide .. 4 cells. Each has half the number of chromosomes as original.

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Genetics

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	Created by georgina.bonnor over 11 years ago