Probability and Punnett Squares

1. Probability and Punnett Squares

2. Probability • Probability is the likelihood that a particular event will occur. • For example: whenever you flip a coin, the probability of it landing heads up is ½ or 50% • If you were to flip it three times in a row, the probability of it landing heads every time would be: • ½ x ½ x ½ = 1/8 • Past outcomes do not affect future ones.

3. Genetics and Probability • The principles of probability can be used to predict the outcomes of genetic crosses • The probability of winning the lottery? • 80 million to one

4. Punnett Squares • Punnett Squares can be used to predict and compare the genetic variations that will result from a cross.

5. Punnett Squares • Gametes of F1 generation along top and left • Possible F2 generation offspring in squares of box • In this cross, B represents the dominant allele for blossom color

6. Punnett Squares • Organisms that have two identical alleles for a trait are said to homozygous (BB or bb) • These are true-breeding organisms • Organisms that have two different alleles for a trait are said to be heterozygous (Bb) • These are hybrid organisms

7. Phenotype/Genotype • Phenotype is the physical characteristics represented by a gene • Example: Purple blooms • Genotype is the genetic makeup • Example: BB or Bb are both genotypes for purple

8. Probability and Segregation • ¼ of the plants have two alleles for purple blooms (BB) • 2/4 have one allele for purple and one for white (Bb) • ¼ have two alleles for white (bb) • Overall, there are ¾ with purple blooms. • Therefore, the ratio of purple to white blooms is 3:1. • Segregation occurred according to Mendel’s model