9 - Genetic Diversity

• What is a gene mutation?

  A change in the base sequence of the DNA.
• When in the cell cycle do gene mutations occur?

  During DNA replication (S phase)
• What is a mutagenic agent?

  Radiation and chemicals increase the risk of mutations
• Give two reasons why gene mutations may not cause a change to the primary structure of a protein?

  1. The genetic code is degenerate, so the new triplet of bases may still code for the same amino acid.
  2. If the mutation occurs in an intron.
• What are the 2 types of gene mutation?

  • Substitution
  • Deletion

  
• Mutations in the number of chromosomes can arise spontaneously. What is a chromosome mutation and when in the cell cycle do they occur?

  Changes in the number of chromosomes and this can arise spontaneously by chromosome non-disjunction during meiosis
• What is non-disjunction?

  Non-disjunction is when the chromosomes or chromatids do not split equally during anaphase.
• What is polyploidy?

  Changes in whole sets of chromosomes occur when organisms have three or more sets of chromosomes rather than the usual two
• What is aneuploidy?

  A change in the number of individual chromosomes.
• What is this a diagram of?

  Polyploidy

  
• What is this a diagram of?

  Aneuploidy

  
• Genetic variation can be introduced in a variety of ways such as during meiosis cell division, mutations and the random fertilisation of gametes.

  
  

  Meiosis cell division creates genetically different gametes. Unlike in mitosis, there are two nuclear divisions in this process which results in four haploid daughter cells.
• What is haploid?

  Haploid (n) = one copy of each chromosome
• What is diploid?

  Diploid (2n) = two copies of each chromosome.
• What key processes produce genetic differences in meiosis?

  • Independent segregation
  • Crossing over
• How does crossing over introduce variation?

  • Crossing over occurs in meiosis I.
  • When homologous pairs line up opposite each other at the equator in meiosis 1, parts of the chromatids can become twisted around each other.
  • This puts tension on the chromatids, causing pairs of the chromatid to break. The broken parts of the chromatid recombine with another chromatid (genetic recombination).
  • This results in new combinations of alleles in the gametes.
• How does independent segregation introduce variation?

  • In meiosis I, homologous pairs of chromosomes line up opposite each other at the equator of the cell.
  • It is random which side of the equator the paternal and maternal chromosomes from each homologous pair lie.
  • These pairs are separated, so one of each homologous pair ends up in the daughter cell.
  • This creates a large number of possible combinations of chromosomes in the daughter cells produced

  
• What is genetic diversity?

  The number of different alleles in a population.
• What is a gene pool?

  All the genes and alleles in a population at a particular time
• What is evolution?

  A change in the allele frequency over many generations.
• What is the advantage of natural selection?

  Natural selection results in species becoming better adapted to their environment.
• What are the three key types of adaptations?

  1. Anatomical
  2. Physiological
  3. Behavioural
• Natural selection leads to evolution within a population. What is the process of natural selection ?

  1. Random mutations occur within the population
  2. This introduces genetic variation to the population.
  3. Some mutations are harmful, sometimes new alleles created by mutations provide an organism with an advantage to survive in their environment.
  4. The new allele provides a reproductive selective advantage. The individual with the allele is more likely to reproduce and pass the allele onto their offspring.
  5. Over many generations, there is an increase in the allele's frequency within the population.
• What is stabilising selection?

  1. The modal trait has a selective advantage.
  2. Occurs when there is no change in the environment.
  3. The modal trait remains the same.
  4. Standard deviation decreases, as individuals with the extreme trait decrease.
• What is directional selection?

  1. One of the extreme traits has a selective advantage.
  2. Directional selection occurs when there is a change in the environment.
  3. The modal trait changes.