1. Applying Mendel’s Principles Probability, Punnett Squares, & Independent Assortment (Dihybrid Cross)
Section 11.2

2. Mendel’s Data
Mendel’s pea plant data gave him a lot of data to analyze
He began observing patterns, for example a cross of two heterozygous parents for tallness always results in approximately ¾ tall & ¼ short
Concluded the principles of probability could be used to explain the results of his genetic crosses

3. Probability
Probability: the likelihood that a particular event will occur
Using flipping a coin as an example:
Two possible outcome
The chance or probability is equal you will get heads or tails and that probability is 1 out of 2 ( ½ or 50%) for heads and 1 out of 2 (½ or 50%)for tails
Each flip is independent
Flip three times in a row – probability of getting heads
½ X ½ X ½ = 1/8
1/8 chance of getting heads three times in a tow
Past outcomes do not affect future ones

5. Probability & Punnett Squares
Predicts averages:
Punnett squares use mathematical probabilities to help predict genotype and phenotype combinations in genetic crosses

6. Independent Assortment
After showing alleles for a trait segregate during meiosis, Mendel began wondering if the segregation of one pair affected the segregation of another
For example: does the gene that affects the shape of the seed affect the gene for seed color?
He then began to follow two traits (two genes) – these are called two-factor or dihybrid crosses

7. Mendel’s Dihybrid Data & Conclusions
Crossed parents that were heterozygous for two traits
Seed shape: R is dominant over wrinkled r
Seed color: Y is dominant over green y
So the parents were RrYy (round yellow )
The offspring resulted in:
Round, yellow (RRYY & RrYy)
Round, green (RRyy & Rryy)
Wrinkled, yellow (rrYY & rrYy
Wrinkled, green (rryy)

8. …continued
Because allele combinations not found in either parent were present in offspring, it showed that alleles for seed shape segregated separately from alleles for seed color - & can result in new combinations
These genes did not influence each other’s inheritance
Principle of independent assortment: genes for different traits segregate independently of each other during meiosis (the formation of gametes)