B9 genetic diversity + adaptation

• a mutation is a change in the base sequence or quantity of DNA of an organism
• a change in the base sequence of a gene can cause the sequence of amino acids to change, or it can not as the genetic code is degenerate so the new triplet may code for the same amino acid
• substitution mutation = a base or group of bases is removed and replaced with a different base or group of bases
• deletion mutation = a base or group of bases is removed and not replaced
• a frame shift is when a number of bases is added to or removed from the sequence which causes all the bases after it to be shifted along in the triplets, so most amino acids are different
• chromosome mutations are changes in the structure or number of whole chromosomes, they arise spontaneously
• the two forms of chromosome mutation are:

  • polyploidy
  • non-disjunction
• polyploidy is changes in whole sets of chromosomes, organisms have multiple sets of chromosomes instead of the typical 2 sets
• non-disjunction is changes in the number of individual chromosomes, individual homologous pairs of chromosomes fail to separate during meiosis, so gametes have too many or too few chromosomes
• mitosis produces two daughter cells with the same number of chromosomes as the parent cell
• meiosis produces four daughter cells with half the number of chromosomes as the parent cell
• in meiosis, the parent cell is diploid and the daughter cells produced are haploid
• genetic variation in meiosis is achieved by:

  • independent segregation of homologous chromosomes
  • crossing over to produce new combinations of alleles
• independent segregation = homologous chromosomes line up in pairs, the pairing is random so division into the daughter cells is random
• crossing over = homologous chromosomes line up, chromatids twist round each other, parts break off and rejoin on the other chromatid, usually equivalent parts are swapped, new combinations of alleles are produced
• meiosis process:

  • (meiosis 1)
  • homologous chromosomes pair up
  • chromatids twist round each other
  • potential for crossing over
  • cell divides into two daughter cells, each with one homologous pair of chromosome
  • (meiosis 2)
  • chromatids move apart
  • daughter cells divide into two, producing four daughter cells each with one chromatid
• a population is a group of individuals of the same species who live in the same place and are able to breed with each other
• a species consists of one or more populations
• genetic diversity is the total number of different alleles in a population
• the greater the number of alleles in a gene pool of a population, the greater the genetic diversity, so the greater the chance that the population would survive a change in environment
• the niche of a species is its role within its environment
• if two species have the same niche, they will compete with each other
• natural selection is the process of individuals who are better adapted to a specific environment being more likely to survive and reproduce, and therefore pass on the advantageous alleles to their offspring
• natural selection process:

  • there must be a variety of different phenotypes within the population
  • an environmental change occurs so the selection pressure changes
  • some individuals have advantageous alleles, they are more likely to survive and reproduce
  • advantageous alleles are passed onto their offspring
  • over time, the frequency of alleles in the populations changes, this is evolution
• evolution is the process of the frequency of alleles in the gene pool changing over time, caused by natural selection
• directional selection = environmental conditions change, the more extreme phenotypes most suited to the new conditions are more likely to survive and reproduce
• over time with directional selection, the mean moves in the direction of the more extreme phenotypes, either to the left or right
• stabilising selection = environmental conditions stay the same, the less extreme phenotypes most suited to the same conditions are more likely to survive and reproduce
• over time with stabilising selection, the mean stays in the same place, but the range decreases and the peak gets higher
• organisms can be adapted in different ways:

  • anatomical = physical changes, can be internal or external
  • physiological = changes to processes in the body
  • behavioural = changes to their behaviour