Genetics, Diversity & Classification

• Translation is where a polypeptide chain is created with mRNA & TRNA
• Process of Translation

  1. A ribosome becomes attached to the starting codon at the end of the mRNA molecule
• What is a phenotype

  An expressed physical characteristic
• What is a genotype

  Genes that you carry
• What is genetic diversity

  The total number of different alleles in a population
• Why is variation important to genetic diveristy

  Due to different alleles being made different phenotype can have favorable traits helping them survive
• What is directional selection

  Individuals with alleles for a single extreme phenotype are more likely to survive and reproduce

  Occurs in response to environmental change
• What is stabilising selection

  Individuals with characteristics towards the middle of the range are most likely to survive and reproduce

  occurs when the environment isnt changing
• What happens if the genetic diversity is too high in stabilising

  In stabilising selection the phenotypes with successful characteristics are preserved and those of greater diversity are reduced
• What happens if your in the middle region for stabilising selection

  the individuals closest to the mean are favoured because they have the alleles that have given them the survival advantage. The furthest from the mean are selected against.
• give four structural differences between a DNA molecule and an mRNA molecule.

  DNA- Deoxyribose, double helix, has thymine and has hydrogen bonds.

  mRNA- ribose, single stranded, has uracil and has no hydrogen bonds.
• What is a gene?

  A sequence of DNA (nucleotides) bases that codes for a polypeptide
• Describe how the production of messenger RNA (mRNA) in a eukaryote cell is different from the production of mRNA in a prokaryote cell.

  Pre-mRNA (only) produced in eukaryote (cell);

  2. Splicing only occurs in eukaryote (cell);

  3. Introns removed in eukaryote (cell)
• Describe the role of ATP in the process of translation in protein synthesis.

  ATP provides energy, so peptide bonds form between amino acids.
• Describe how the process of meiosis results in haploid cells.

  Do not include descriptions of how genetic variation is produced in meiosis.

  DNA replicates during late interphase, and then separation of chromosomes occur in division 1, and then separation of sister chromatids in division 2, and produces 4 cells
• What does stabilising selection to do to extreme phenotypes?

  Extreme phenotypes are selected against.
• Which stage of meiosis does crossing over occur?

  Metaphase I
• What are the chiasma?


  Point where chromatids break
• What is swapped during crossing over?

  Different alleles of the same gene
• Why cant non homologous pairs of chromosomes swap over?

  They have different genes and the resulting cells would have too many copies
• How does crossing over increase genetic variation?

  Each 4 new cells formed from meiosis contains chromatids with different combinations of alleles
• What are the 3 causes of genetic variation during meiosis

  1. Crossing over
  2. Independent assortment of homologous chromosomes in meiosis I
  3. Independent assortment of chromatids in meosis II
• Define meaning of selection pressure

  a factor that will either drive evolution through natural selection or ultimately cause the demise of a species r population
• How is low genetic diversity caused

  Very small populations where inbreeding occurs as this reduce the number of allelles
• Explain what is stabilising selection and describe circumstances in which it takes place?

  Stabilising selection refers to a reduction in phenotypes ​

  As only alleles that are centred towards the middle range or mean are more likely to survive.​

  This is due to organisms possessing favourable alleles​

  This typically occurs in stable environments whereby there are not extreme fluctuations in biotic or abiotic factors​
• 5 human factors that influence biodiversity

  • Deforestation
  • Pesticides and Herbicides
  • Fertilisers and Eutrophication
  • Mono culture Modern farming
  • Hedgerow removal
• Crossing over greatly increases genetic diversity, describe the process

  Homologous chromosomes join together forming a bivalent, chiasmata form, equal lengths of non sister chromatids are exchanged, producing new combinations of alleles
• What is species richness

  Is a measure of different number of different species In a community
• What is deforestation and why is it bad

  • increases area for farmland
  • reduces number of trees
  • destroys habitats
• What s removal of hedgerow and why is it bad

  • Done to increase area for farmland
  • Reduces trees and tree species
• What is monoculture and why is it bad

  Produces only 1 crop

  Directly reduces diversity

  Can only support fewer organisms and habitats food
• What is Pesticide and Herbicide and why is it bad

  Directly kills pests and organisms that feed on them affects food chain. Herbicides reduce plant diversity and animals that feed on them
• What is index of diversity data used for

  Can be used to compare biodiversity of different ecosystems or monitor change of biodiversity in a community overtime
• What is the problem with comparing base sequence?

  Two species may have have same amino acid sequence but different DNA base sequences because the genetic code is degenerate, therefor protein comparisons are less useful for closely related organisms
• How has the study of genetic diversity measured been changed overtime

  1. Used to be measured by observable characteristics advances in gene technology has caused this to be replaced why
  2. Either Direct study of base sequences of dna OR direct study of base sequences of mRNA OR study of amino acid sequences of the proteins encoded by DNA or Mrna
• What is a mutation?


  Involves a change of DNA base sequences of chromosomes, more likely to occur during replication
• What is base substitution?

  1 base is substituted for another, not s harmful as the deletion. Only 1 codon is changed but R groups can change=Different bonds formed= Different tertiary structure. However often the genetic code is degenerate not all bases cause change in amino acids
• What is base deletion?


  1 base is lost causes frame shift to the right is harmful because every codon is now different, changes amino acid sequence so polypeptide produced is completely different and maybe dysfunctional
• How does Meiosis cause variation

  • Independent segregation, Each homologous chromosome is made up of 1 chromatid from parents, in Meiosis 1 they are separated in random order, causing disruption in daughter cells
  • Crossing over, homologous chromosomes come together and pair up, and chromatids twist around each other and bits of chromatids end up with different combos of alleles
• How does Non-Disjunction cause variation


  When sister chromatids don't separate properly during meiosis, leading to uneven distribution of chromosomes, can occur in both Meiosis 1 and 2 if its in sexual repro zygote have an extra pair or only 1 pair