knowledge-3 GVA

• Genetic diversity can arise as a result of mutation or during meiosis. A mutation is a spontaneous change in the base sequence of a chromosomes.
• Base insertion or deletion:

  One base is inserted or deleted , causing the base triplet composition of amino acids to change along the entire polypeptide chain after the mutation. This is known as frameshift.
• Base substitution:

  One base is substituted for another base , causing a change in the genetic code and amino acid composition of a protein. However this does not always change the resulting polypeptide chain as the genetic code is degenerate.
• mutagenic agents:

  mutagenic agents are chemicals or radiation that lead to an increase in the rate of gene mutation. For example:

  • ionizing radiation
  • some viruses and micro-organisms
  • unhealthy diet
  • asbestos
• meiosis has the random fertilization of the haploid gametes which increases genetic variation in a species.
• Spontaneous mutations can arise because chromosomes fail to split into separate daughter cells , resulting in a lower or higher number of chromosomes in those cells.
• Non-disjunction (meiosis only) can occur during anaphase 1 , when homologues fail to separate affecting four daughter cells or in anaphase 2 where sister chromatids fail to separate affecting two daughter cells.
• Mitosis:

  • forms somatic cells
  • diploid to diploid or haploid to haploid
  • genetically identical daughter cells
  • no independent segregation
  • no crossing over
• Meiosis:

  • forms gametes
  • diploid to haploid
  • daughter cells genetically different
  • four daughter cells produced
  • homologous chromosomes randomly segregated in meiosis 1
  • non-sister chromatids in prophase one can cross over and exchange information.
• Crossing over:

  when homologous chromosomes cross-over , there is even more genetic variation amongst daughter cells.

  1. chromatids of homologous chromosomes twist around one another , crossing over many times.
  2. in a single crossing over on each chromosome a equal piece of each stand is broken and swapped.
• there are three types of adaptations:

  1. anatomical adaptations- such as water fleas in environment with more predators have a thicker exoskeleton compared to water fleas in environment of less predators
  2. Physiological adaptations- such as yaks that live in high altitudes having higher red blood cell count to support living in low-oxygen environments
  3. Behavioral adaptations- such as courtship rituals in birds.
• Directional selection:

  where there is a change in conditions resulting in extreme genotypes/ phenotypes being advantageous. This leads to those with advantageous genes surviving and reproducing until the number of individuals with that gene becomes the norm.