biology 12.2

• probability is the likelihood that a particular event will occur

  • past outcomes do not affect future ones

  • way in which alleles segregate during

  gamete formation is completely random

  and can be analyzed using probability

  • probabilities predict average outcome of

  a large number of events

  • the larger the number of offspring, the

  closer results will be to predicted values
• homozygous organisms have 2 identical alleles for a particular gene (GG, gg, TT, tt)
• heterozygous organisms have 2 different alleles for a particular gene (Gg, Tt)
• phenotypes are physical traits (tall, short)
• genotypes are genetic makeup (TT, Tt, tt)
• punnett squares use probability to help predict genotypes

  & phenotypes in genetic crosses

  • all possible combinations of alleles in

  gametes produced by each parent are

  shown along top & left sides of square

  • every possible genotype is written inside

  the boxes within square
• the two-factor cross follows 2 different genes as they pass

  from one generation to the next and is also called a dihybrid cross

  • Punnett Square will have up to 16 boxes

  • RrYy x RrYy cross will result in a 9:3:3:1

  phenotypic ratio in next generation
• the principle of independent assortment states that genes for different traits can segregate independently during formation of gametes (genes do not influence each other’s inheritance)
• Mendel’s Principles:

  • inheritance of biological characteristics is

  Principles determined by individual units called

  genes, which are passed from parents to

  offspring

  • where 2 or more alleles of the gene for a

  single trait exist, some alleles may be

  dominant and others may be recessive

  • each adult has 2 copies of each gene – 1

  from each parent; these genes segregate

  from each other when gametes are

  formed

  • alleles for different genes usually

  segregate independently of each other