Variation and Inheritance

• Variation


  Characteristics such as eye colour, height and body mass differ between individuals in a population. These differences are called variation.
• Variation


  • Occurs during sexual reproduction, when genes from two parents are combined
• Types of variation


  • Discrete
  • Continuous
• Discrete variation


  Phenotypes fall into distinct groups, is not affected by environmental factors so does not change over time
• Continuous variation


  Phenotypes have a range of values, can be affected by environmental factors so can change over time
• Genotype


  Alleles an organism has for a characteristic (pair of letters)
• Phenotype


  Physical characteristic of a genetic trait
• Dominant


  Allele that is always present in an organism's phenotype, represented with a capital letter
• Recessive


  Allele that is hidden from the phenotype by a dominant allele, must inherit two recessive alleles to show the recessive phenotype
• Homozygous


  Genotype contains two of the same allele
• Heterozygous


  Genotype contains two different alleles, these individuals show which characteristic is dominant as they have both forms of the gene
• P generation


  Parent generation
• F1 generation


  First generation (offspring of the parents)
• F2 generation


  Second generation (offspring of the first generation)
• Alleles in mice


  • B-brown fur; b-white fur; L- long tail; l- short tail, R- round ears; r- pointed ears
• LL is homozygous, Bb is heterozygous, BB is homozygous
• Phenotypes for the given genotypes are: long tail, brown fur, round ears