Genetic diversity can arise - mutation and meiosis

• Haploid


  - one copy of each chromosome in a cell

  
• Diploid


  - two copies of each chromosome in a cell

  
• Meiosis


  - cell division that creates genetically different gametes

  - there are two nuclear divisions in this process

  - results in four haploid daughter cell

  
• Independent segregation


  - homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell

  - when they separate it creates a large number of possible combinations of chromosomes in the daughter cells produced
• Crossing over


  - homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1 - parts of the chromatids twist, break and recombine with another chromatid

  - results in new combinations of alleles in the gametes

  
• Gametes


  - sex cells (sperm and egg)
• How does meiosis introduce variation?


  - crossing over independent segregation
• Types of gene mutations


  - substitution

  - insertion

  - deletion
• What is a frameshift?


  - the removal of one base changes all of the subsequent codons

  - all the bases shift back one position
• Chromosome mutation


  - change in the number of chromosomes

  - occurs during meiosis
• Deletion mutation


  - a gene mutation

  - a base is removed from a sequence

  - causes a frameshift
• Substitution mutation


  - a gene mutation

  - a base is swapped for a different one
• Non-disjunction


  - the chromosomes or chromatids do not split equally during anaphase

  
• Polyploidy


  - changes in whole sets of chromosomes

  - e.g. when organisms have three or more sets of chromosomes

  - mainly occurs in plants

  
• Aneuploidy


  - a change in the number of individual chromosomes

  - e.g 3 copies of chromosome 21
• Down's syndrome


  -causes by a chromosome mutation

  - an example of aneuploidy

  - 3 copies of chromosome 21
• Genetic diversity


  - the number of different alleles in a population