Topic 6 - Inheritance, Variation and Evolution

DNA
1. Deoxyribonucleic acid
2. It contains oded information that are used to create another cell.
3. this will determine what inherited characteristics you will have.
4. Found in the nucleus
5. chromosomes come in pairs.
6. DNA is a polymer. it is made up of two strands coiled together in the shape of a double helix.
7. Gene codes for a specific protein.
  1. a gene is a small section of DNA found on a chromosome
  2. Each gene codes for a particular sequence of amino acids, which are put together make specific proteins.
  3. Only 20 amino acids are used, but they make up thousands of different proteins.
  4. Genes tell cells what order to put amino acids together
  5. DNA also determines what proteins the cell produces.
  6. that in turn determines the type of cell it will produce.
8. Every organism has a GENOME
  1. genome means - the entire set of genetic material in an organism
  2. it allows scientists to identify genes in the genome that are linked to types of disease.
  3. Knowing which genes link to inherited disease could help to provide and develop effective treatments.
  4. Scientists can look at the genomes to trace the migration of certain populations.
    1. All modern humans came from one ancestor from Africa, but humans can be found all over the world. The human genome is mostly identical, but as people migrated away from Africa little changes appeared. By investigating the genome scientists can discover when new populations split off in different direction and find what route they took.
The structure of DNA and protein synthesis.
1. DNA is made up of Nucleotides
  1. DNA is a polymer made up of lottos repeating units called nucleotides
  2. Each nucleotide consists of one sugar molecule, one phosphate molecule and one base.
  3. The sugar and phosphate molecules form the 'backbone' to the DNA strands.
    1. the sugar and phosphate molecules alternate
    2. one of four different bases join to each sugar.
      1. A
      2. T
      3. C
      4. G
  4. Each base links to a base on the opposite side.
  5. A+T C+G
    1. This is called complementary base pairing.
  6. it is the order of bases that decides the order of amino acids in a protein.
2. mRNA carries the code to the ribosomes
  1. to make proteins, ribosomes use the code in the DNA.
  2. this is done using a molecule called mRNA - which is copying the code form DNA, mRNA acts as a messenger.
  3. the correct amino acids are bought to the ribosomes in the correct order by carrier molecules.
Mutations
1. Are changes in the genetic code
2. Can be inherited.
3. Most mutations have little to no effect on a protein in the genetic code.
4. However some mutations can seriously affect a protein, by changing their shape.
5. Different types of mutations
  1. Insertions
    1. Where a new base Is inserted when it shouldn't be.
    2. An insertions changes the way the groups of three bases are 'read', which changes the amino acids they code for.
    3. Can change more than one amino acid and have a 'knock on' effect on other bases further on in the sequence.
  2. Deletions
    1. Where a random base is deleted from the sequence.
    2. Can also have 'knock on' effects further down the sequence.
  3. Substitutions
    1. Where random bases in the sequence are changed to a different base
Reproduction.
1. Sexual
  1. transfer of genetic information from twi 'parents' to produce offspring that are genetically different to either parent.
    1. Involves male and female gametes - offspring has a mixture of parent's genes.
  2. 'parents' produce gametes by meiosis.
  3. In humans gametes contain 23 chromosomes - half the number of chromosomes in a normal cell.
  4. this is why offspring inherits features from both parents - it's a mixture of chromosomes.
  5. mixing genetic information produces variation in offspring.
  6. Advantages over asexual reproduction
    1. Offspring have a mixture of two sets of chromosomes, producing variation.
    2. Variation increases the survival of a species in a changing environment. They have survival advantages.
    3. Individuals with characteristics that make them better adapted are more likely to breed successful and pass their genetics on. This is called natural selection.
    4. You can use selective breeding to 'speed up' natural selection. This produces animals with desirable characteristics.
2. Asexual
  1. Only one parent, so the offspring are genetically identical.
  2. This happens by mitosis - an ordinary cell divides into two.
  3. the new cell has exactly the same genetic information - called a clone.
  4. bacteria, some plants and some animals produce this way.
  5. Advantages over sexual reproduction.
    1. There only needs to be one parent
    2. this uses less energy because the organism doesn't have to find a mate.
    3. this means asexual reproduction is faster.
    4. Many identical offspring can be produced in favourable conditions.
3. Meiosis
  1. gametes only have one copy of each chromosomes, so that when gamete fusion happens there is the correct amount.
  2. Only happens in the reproductive organs.
  3. 1. before the cell starts to divide it duplicates its genetic information, after they replicate, the chromosomes go into pairs.
  4. 2. The first division in meiosis the chromosomes pairs line up in the centre of the cell.
  5. 3. The pairs are the pulled apart, so each new cell only has one copy of each chromosomes, some from the father and some from the mother.
  6. 4. Th second division, the chromosomes line up again, the arms of the chromosomes are pulled apart.
  7. Gamete fusion replicates itself.
    1. After two gametes have fused during fertilisation, the resulting new cell dividing by mitosis to make a copy of itself.
    2. Mitosis repeats many tamest produce lots of new cells in an embryo.
    3. as the embryo develops, these cells then stat to differentiate into the types of specialised cells that make up a whole organism.

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Topic 6 - Inheritance, Variation and Evolution

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