mutations and meiosis

• what do gene mutations involve

  a change in the base sequence of chromosomes
• are mutations spontaneous

  yes
• when do mutations occur

  spontaneously during DNA replication
• what are the two types of mutations

  base deletion and substitution
• what happens when a base is substituted

  a nucleotide in a DNA molecule is replaced by another nucleotide which has another base
• why might the substitution of bases have a negative outcome

  the polypeptide produced will differ by one amino acid which affects the tertiary structure, if this is an enzyme it will alter its active site shape
• why might the substitution of bases have no affect

  the genetic code is degenerate
• what happens when a base is deleted

  when a nucleotide is lost from the DNA sequence
• what does the deletion of bases cause

  each nucleotide to be shifted to the left one meaning all triplets are read differently
• what can increase the rate of gene mutation

  mutagenic agents
• what is a chromosome mutation

  a change in the number or structure of whole chromosomes
• give two types of chromosome mutations

  polyploidy and non-disjunction
• what is non-disjunction

  when individual homologous pairs of chromosomes fail to separate during meiosis
• what does non-disjunction cause

  a gamete having either one more or one fewer chromosome
• what is a homologous chromosome 


  a pair of chromosomes, one maternal one paternal that have the same gene loci
• what is an allele

  one of the different forms of a particular gene
• what is a locus

  the position of a gene on a chromosome or DNA molecule
• how does mitosis and meiosis differ

  mitosis produces two genetically identical daughter cells with the same number of chromosomes as parent cell

  meiosis produces four non-genetically identical daughter cells that have half of the number of chromosomes as its parent cell
• what is independent segregation 


  it happens in meiosis 1, it is the random separation of homologous chromosomes which produces genetic variation
• what is crossing over


  - chromatids of each homologous pairs become twisted around eachother

  - tensions are created and portions of the chromatids break off

  - these broken portions may the rejoin with the chromatids of homologous partner via recombination

  - now new genetic combinations of maternal and paternal alleles are produced