Inheritance, Variation & Evolution

• Give 2 examples of inherited disorders?

  • Polydactyly (homozygous dominant allele)
  • Cystic fibrosis (homozygous recessive allele)
• What is inherited disorder?


  Disorder that is caused by the inheritance of certain alleles
• What are alleles?


  Different forms of gene
• What is genotype?


  The alleles
• What is phenotype?


  Physical characteristics
• What is homozygous?


  Both alleles of an organism are the same
• What is heterozygous?


  The alleles of an organism are different
• Some characteristics are controlled by a single gene.

  • Fur colour in mice
  • Red-green colour blindness in humans
• A dominant allele is always expressed, even if only one copy is present (75%)
• A recessive allele is only expressed if two (both) copies are present (no dominant ,25%)
• Most characteristics are a result of multiple genes interacting, rather than a single gene
• What the name of the diagram to determine the expected percentages of different genotypes in the offspring of two parents?

  Punnett square
• How many chromosomes do ordinary human body cells contain?

  46 (23 pairs)
• 22 pairs of chromosomes control characteristics only but one of the pairs carries the genes that determine sex

  • Female: XX (same chromosome)
  • Male: XY (different chromosome)
• What is variation?


  The difference in the characteristics of individuals in a population
• What cause variation in individuals?

  • The genes they have inherited (genetic causes)
  • The conditions in which they have developed (environmental causes)
  • A combination of genes and the environment
  • —>There is usually extensive genetic variation within a population of a species
• All variants arise from mutations, which

  • most have no effect on the phenotype
  • some influence phenotype
  • very few determine phenotype
• Mutations occur continuously in the genome, but very rarely a mutation will lead to a new phenotype
• If the new phenotype is suited to an environmental change, it can lead to a relatively rapid change in the species