Genetic diversity due to mutation or meiosis

• What is mutation?

  A change in base sequence of chromosomes. This can arise spontaneously during DNA replication.
• Define Base substitution

  A silent mutation occurs when substitution of a base still codes for the same amino acid as the original base(due to degenerate nature of the genetic code). This has no effect on the final polypeptide.
• Define Missense Mutations

  Substitution where one amino acid can be changed to another due to the substitution of a new base.
• Why can missense mutations have very little effect on a protein?

  A new amino acid may be similar to the old amino acid or the missense mutation may be in a region when the function of protein is not affected.
• What serve effects can a missense mutation cause?

  It can affect the tertiary structure.
• What is Non-sense mutation?

  A mutation where the substitution of a base sequence leads to a stop codon.
• Examples of stop codons

  UAA, UAG, UGA
• What does a non-sense mutation result in?

  A short polypeptide (The protein would not be able to function properly)
• What do insertions and deletions result in ?

  Leads to a frame shift (the entire amino acid sequence will be different) and may lead to premature termination.
• Give examples of mutagenic Agents

  X-rays and gamma rays, UV light , and certain chemicals e.g. tobacco or alcohol.
• What is a mutagenic Agent?

  Factors that can increase the frequency/rate of gene mutations
• What changes in chromosome mutations?

  The structure or number of chromosomes
• What is a polyploidy (chromosome mutation mostly found in plants)

  Changes in the whole set of chromosomes. 3 or more sets of chromosomes rather than 2 sets.
• What happens during meiosis 1 ?

  homologous chromosomes separate (reduction division - reduction of number of chromosomes to half the normal number)
• What happens during meiosis 2 ?

  Sister chromatids are separated similar to mitosis ( Mitosis style)
• During meiosis 1 , prophase 1 occurs. What happens during prophase 1?

  When homologous chromosome pair up, foursomes (with their duplicated arms) are called tetrad or a bivalent.
• Where does crossing over occur during meiosis

  It occurs at chiasmata. Chiasmata is the positions at which non-sister chromatids appear joined together.
• Prophase 1 


  The non-sister chromatids of the homologous pair swap/ exchange segments or alleles. The segments that get swapped represent different alleles. This leads to new combinations of chromosomes called recombinants (new sequence of genes).
• Sister chromatids cannot cross over during prophase 1 as they have the same genetic information although they may have different alleles. These arms that did not cross over are called recombinants.

  
• Give 2 ways in which meiosis produces genetic variation

  Crossing over during meiosis 1. Independent assortment ( random segregation of homologous chromosomes and sister chromatids.
• What occurs during prophase 1 ?


  Crossing over