1. Segregation (p. 311 and 312) Segregation = separation
The alleles for tall vs. short separate during the formation of gametes – sex cells
Each gamete carries one allele for each gene
Why we can get two tall plants from a tall and short cross.

2. 11-2 Probability and Punnett Squares
Mendel realized…the principles of probability could be used to explain the results of genetic crosses.

3. Genetics and Probability
Probability – the likelihood a particular event will occur.
Ex: probability of flipping a coin to heads = ½ or 50%
Probability of head 3 times in a row = ½ x ½ x ½ = 1/8
The greater the number or trials, the closer to the expected ratio
Past outcomes do not affect future outcomes
Alleles segregate randomly (like a coin)

4. Probabilities Predict Averages
To get an accurate prediction of flipping a coin – the coin should be flipped many times and an average taken.
In genetics …the more offspring you get, the closer to the predicted ratio.

5. Punnett Squares
Punnet square – diagram to predict and compare outcomes of genetic crosses.
Homozygous – organisms that have 2 identical alleles for a particular trait
True-breeding for a particular trait
Ex: TT or tt

6. Punnett Squares
Heterozygous – organisms that have 2 different alleles for the same trait
Hybrid for that trait
Ex: Tt

7. Punnett Squares Phenotype – physical characteristics
Ex: tall, short, yellow, green
Genotype – genetic make-up
Ex: TT, Tt, tt
Tall plants have the same phenotype (tall), but not the same genotype (TT or Tt)
Why are TT and Tt genotypes for tallness, but tt is not???

8. Independent Assortment
Mendel questioned how alleles segregate
Does it happen independently?
Ex: Does the seed shape gene influence the seed color gene????
INDEPENDENT ASSORTMENT
Need to follow 2 diff. alleles from one generation to the next.

9. The Two-factor Cross: F1
4 alleles (2 genes) at the same time
Provides the hybrid plants (F2 generation)
Crossed a homozygous RRYY (round yellow peas) with a homozygous rryy (wrinkled, green peas)

10. The two factor cross: F2
F1 – yields all offspring heterozygous for both traits
F2 – heterozygous parents crossed
F2 – yields 9:3:3:1
ratio

11. Mendel discovered the principle of
Independent assortment – genes segregate independently during the formation of the gametes
Helps account for many genetic variations in organisms
Seed shape & color gene do not influence each other

12. Ttrr x ttRr

13. ttRr x TtRr

14. Mendel Questions
Using tall and short pea plants and the letters T = dominant and t = recessive describe Mendel’s F1 generation and F2 generation.
Provide the genotype and phenotype for each of four offspring from each generation. You do not need to use a punnett square.

15. Meiosis