KA 4: Variation and Inheritance

• What are the two types of variation?

  Discrete and continuous variation
• Give two examples of discrete variation.

  Eye colour and blood group
• What distinguishes discrete variation from continuous variation?

  Discrete variation has clear cut differences
• What is polygenic inheritance?

  Influence of many genes on a characteristic
• What type of inheritance do discrete characteristics follow?

  Single gene inheritance
• What are different forms of characteristics called?

  Phenotypes
• What is a monohybrid cross?

  Cross involving one characteristic over generations
• What is the first generation in a monohybrid cross called?

  Parental (P) generation
• What is the second generation produced from the F1 generation called?

  Second filial (F2) generation
• What does it mean for an organism to be homozygous?

  It has two identical alleles for a characteristic
• What is the phenotype of an organism?

  The observable characteristics of an organism
• What happens when homozygous parents with different phenotypes are crossed?

  F1 offspring show only one phenotype
• What is the expected phenotypic ratio of F2 offspring in a monohybrid cross?

  3 dominant to 1 recessive
• Why might the phenotypic ratio in the F2 generation differ from expectations?

  Fertilisation is random or few offspring
• How are dominant and recessive forms of genes represented?

  Capital letter for dominant, lowercase for recessive
• Where are genes located in a cell?

  In the nucleus of cells
• What are alleles?

  Different forms of the same gene
• How are genes passed to the next generation?

  Through gametes (sex cells)
• How many sets of chromosomes do body cells have?

  Two sets of matching chromosomes
• What happens during fertilisation?

  Male and female gametes fuse together
• What is the genotype of an organism?

  The set of genes possessed by an organism
• What is the result of crossing homozygous black and white mice?

  Black coat colour is dominant to white
• How do pedigree charts help in genetics?

  • Follow inheritance patterns in humans
  • Use symbols to represent individuals
  • Squares indicate males, circles indicate females
  • Open symbols for dominant phenotype, filled for recessive
• What do filled-in symbols in pedigree charts indicate?

  Individuals with the recessive phenotype
• What do open (white) symbols in pedigree charts indicate?

  Individuals with the dominant phenotype