Bio- Genetic Variation and Change

• Haploid


  Having one set of chromosomes (n)
• Diploid


  Having two sets of chromosomes (2n)
• Homologous chromosomes


  A pair of chromosomes, one inherited from each parent, each carrying the same genes at the same locus.
• Locus


  Position of a gene on a chromosome
• Sister chromatid


  One of two copies of a replicated chromosome produced during cell division
• Centromere


  The area where sister chromatids are joined together
• Mutation


  Permanent change in the DNA base sequence
• Gametic mutation


  Mutation that occurs in sex cells and can be passed on to offspring during fertilisation
• Somatic mutation


  Mutation that occurs in the DNA of body cells and only affects the individual (not passed on)
• Meiosis


  A type of cell division that produces four genetically different haploid gametes.
• Crossing Over


  The exchange of segments of DNA between homologous chromosomes. Results in each gamete having a different allele combination.
• Independent Assortment


  The random way homologous pairs line up along the equator during meiosis. Results in each gamete having a mix of maternal and paternal chromosomes.
• Segregation


  Pairs of alleles seperate so that each gamete carries one allele per gene. Results in each gamete having a different combination of alleles and only half the chromosomes of the parent cell.
• Recombinants


  Offspring or chromosomes with new allele combinations due to crossing over.
• Centromere


  point where the 2 chromatids are joined together.

  
• Chiasma


  the point at which chromatids break and re-join in crossing-over.
• Homologous pair


  a pair of chromosomes, one from each parent, that have the same genes at the same locus

  
• Diploid


  two complete sets of chromosomes, one from each parent.
• Haploid


  having a single set of chromosomes

  
• Locus


  position of a gene on a chromosome

  
• Meiosis


  type of cell division producing four gametes that are each genetically different, with half the number of chromosomes of the parent cell

  
• Crossing over


  exchange of genetic material between homologous chromosomes during meiosis

  
• Independent assortment


  each homologous pair of chromosomes line up randomly during meiosis I

  
• Segregation


  Pairs of alleles for each gene are separated from each other, so each gamete receives one allele per gene

  
• Chromatid


  one half of a replicated chromosome

  
• Replicated chromosome


  A chromosome that has been copied; consists of two identical sister chromatids

  
• Recombinant gamete


  gamete that possesses new combinations of alleles

  
• Recombinant chromatids


  chromatid containing genetic information from both parents as a result of crossing over

  
• Result of independent assortment


  each gamete is unique and can end up with any combination of paternal or maternal chromosomes
• Result of crossing over


  gametes with new combinations of alleles and therefore new characteristics in the offspring
• Result of segregation


  each gamete carries one allele for each gene and has a different combination of alleles from other gametes
• Co-dominance


  Alleles of a gene in heterozygotes are both independently and fully expressed
• Incomplete dominance


  An allele for a specific trait is not completely dominant over the other, resulting in heterozygotes having an intermediate phenotype
• Lethal alleles


  Allele combinations that code for a phenotype that causes the death of an individual
• Multiple Alleles


  More than two alleles for a gene at a locus
• Allele frequency


  The percentage of each allele in a a gene pool
• Bottleneck effect


  A significant reduction in the size of a population. The allele frequency of the population is unlikely to be representative of the original gene pool
• Centromere


  The area where chromatids are joined together during meiosis
• Emigration


  Movement of organisms out of a population
• Founder effect


  When a new population is established by a small number of individuals from a larger original population. The allele frequency of the new population is unlikely to be representative of the original gene pool.