topic 8

• phenotype - genes expressed in your physical appearance
• genotype - genetic makeup of an individual
• homozygous - both alleles are identical for both characteristics
• heterozygous - one allele is different than the other in the genotype
• dominant genes - only need one allele to be seen in the phenotype
• recessive - needs both alleles to be present to be seen in the phenotype
• codominance - both alleles are expressed equally and contribute to the phenotype
• the hardy wienburg equation is used to tell the percentage of dominance or recessive alleles
• hardy weinburg =

  p + q = 1

  p² + 2pq + q²
• 3 hardy weinburg assumptions:

  1. no mutations occur
  2. random mating occurs
  3. large population size
• autosomal linkage: two or more genes are on the same numbered chromosome
• type A blood - dominant
• type B blood - dominant
• type AB blood - dominant
• Type O blood - recessive
• sex chromosome - XX - female
• sex chromosome - XY - male
• chi squared - the obtained value must be higher than 0.5 for the null hypothesis to be accepted
• chi-squared - degree of freedom = number of categories -1
• chi - squared = used to see if the difference between observed and expected is close enough to be up to chance
• selection pressure - environmental factors that drive evolution by natural selection and limit population sizes (competition, predators and disease)
• stabilising selection - phenotypes with successful characteristics are preserved and those of greater diversity are reduced (babies with average weights are more likely to survive than extremes)
• disruptive selection - both extremes of the phenotypes are favoured over the mean (dark and light coloured moths can camouflage but grey ones cannot)
• directional selection - organisms which adapt to the new environment are more likely to survive (anti-biotic resistance)
• genetic drift - the alleles that are passed on through offspring in sexual reproduction are random selected if the offspring available - gene frequencies will sometimes increase or decrease by chance
• bottle necking:

  • the size of the population may be reduced by an environmental disaster, hunting by humans or other predators
  • many of the genes in the original population are lost so the gene pool shrinks and so does the allele frequency
• founder effect:

  • loss of genetic variation when a small number of organisms leave the main population, the alleles carried by this population are unlikely to include all the allele frequencies
  • many of the genes in the original population are lost so the gene pool shrinks and so does the allele frequency
• chi-squared test

  
• gene locus is the location of a gene on a chromosome
• gene pool is the total number of alleles in a population
• allele frequency is the number of times an allele is seen in a gene pool