Genetic diversity and evolution

• A mutant gene is an altered version of a normal gene that can cause disease or other problems.
• Mutations are likely to occur during DNA replication in interphase of the cell cycle
• Changing one amino acid in the polypeptide chain can alter the protein's function
• Carcinogens interfere with the structure of DNA or transcription
• Types of gene mutations:

  • insertion mutation: one DNA nucleotide is accidentally added, causing a frame shift and altering subsequent bases
  • Deletion mutation: one DNA nucleotide is deleted, causing a frame shift and altering subsequent bases
  • Substitution mutation: one base is swapped, potentially changing the amino acid coded for
  • non disjunction: chromosomes didn't split properly so both sister chromatids go to one pole e.g. down syndrome, Marfan and Turner's syndrome.
  • Translocation mutation: a section of bases on one chromosome breaks off and attaches to a different chromosome
• Types of substitution mutations:

  Silent: When one base in the codon changes, DNA is degenerate so codon still codes for the same amino acid.

  mis-sense: when one whole codon changes so protein cant carry out function as well as it normally could e.g. anemia.

  Non-sense: Stop codon moves so protein finishes prematurely e.g. cystic fibrosis.
• In prokaryotic cells, DNA is short and circular and not associated with any proteins
• In eukaryotic cells, DNA is linear and long and associated with histone proteins
• Coding and non-coding DNA are found within DNA
• Gene: a section of DNA that codes for a polypeptide chain or functional RNA
• Locus: the position of the gene within the DNA
• Allele: different versions of the same gene
• Introns: bits of gene that don't code for anything
• Exons: bits of gene that do code for something
• Homologous chromosomes: matching pairs that may contain different alleles
• Triplet: a three-base pair that codes for an amino acid
• DNA has a degenerate code, allowing more than one triplet to code for an amino acid
• The genetic code is non-overlapping, with each base pair read only once
• Genome: all the genes in a cell
• Proteome: all the proteins that a cell can make
• Transcription: process of creating mRNA from DNA
• mRNA is a single polynucleotide chain smaller than DNA but larger than tRNA
• Translation: process of creating a polypeptide chain from mRNA using tRNA
• Mutation: any change in the genetic code
• Gene mutation: mutations that occur in genes
• Base substitutions: mutations where one base is substituted with another without changing the amino acid
• Base deletions: mutations where a base is deleted, causing a change in the reading frame
• Chromosome mutations: mutations that occur during meiosis
• Mitosis: produces two identical daughter cells
• Meiosis: produces four non-identical daughter cells (gametes)
• Meiosis leads to haploid cells through two nuclear divisions
• Crossing over and independent segregation increase genetic variation in meiosis
• Genetic diversity: the number of different alleles in a population
• Genetic bottleneck: reduction in genetic diversity due to a large population die-off
• Directional selection: favors extreme adaptations due to sudden environmental changes
• Stabilizing selection: favors traits in the middle of the range during stable environmental conditions
• Antibiotic resistance is an example of directional selection
• Antibiotic resistance is an example of natural selection or evolution that happens quickly
• Investigating antibiotic resistance in the lab involves placing antibiotic discs on a plate with bacteria, allowing it to grow, and measuring the clear zones
• Reasons for antibiotic resistance include overuse in animal feed, inappropriate use for viral infections, and incorrect use of antibiotics