1. AP Biology Presentation
By Nana Amoh and Joe Urena

2. Mendelian Genetics
The genetics formulated by Gregor Mendel contain 3 laws:
The Law Of Segregation
The Law of Independent Assortment
The Law of Dominance (Most Visual Law)

3. First Law: The Law or Segregation
Mendel made 2 innovations to the science of genetics
-1. He developed pure lines
-2. He counted his results and kept statistical notes
pure line: a population that breeds true for a particular trait [this was an important innovation because any non-pure (segregating) generation would and did confuse the results of genetic experiments
phenotype: the outward, physical appearance of a particular trait
Dominant: the allele that expresses itself at the expense of an alternate allele

4. Second Law: The Law of Independent Assortment
This law states that different pairs of alleles are passed onto the offspring independently of each other
Therefore, inheritance of genes at one location in a genome does not influence the inheritance of genes at another location

5. Third law: The Law of Dominance
In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation
Offspring that are hybrid for a trait will have only the dominant trait in the phenotype

6. The Pea Plant Experiment

7. In one experiment...
In one experiment, Mendel cross-pollinated smooth yellow pea plants with wrinkly green peas. Every single pea in the first generation crop was as yellow and as round as was the yellow, round parent. Somehow, yellow completely dominated green and round dominated wrinkly. Mendel learned from this that there are two kinds of traits - dominant and recessive. In this case, the dominant traits are the yellow color and the round shape since they show up at the expense of the green color and the wrinkly shape. He also learned that the inheritance of each trait is determined by "units" or "factors" - now called genes. In his experiment Mendel marked with capital letters dominant traits and with small letters recessive traits.
Y = dominant yellow color g = recessive green color R = dominant round shape w = recessive wrinkled shape

8. Mendel came to 3 important conclusions from these experiment results:
That the inheritance of each trait is determined by "units" or "factors" (now called genes) that are passed on to descendents unchanged
That an individual inherits one such unit from each parent for each trait
That a trait may not show up in an individual but can still be passed on to the next generation.

9. Punnett squares
Punnett squares are a useful tool for predicting what the offspring will look like when mating plants or animals. Reginald Crundall Punnett, a mathematician, came up with these in 1905, long after Mendel's experiments. For every gene, different versions called alleles exist. Alleles control things like pea color or the presence of dimples on your face.

10. Actual steps of making a punnet square
Begin by writing the parents' genotypes along the top and side of the Punnet square.
Next, fill in each cell with two alleles, one from the parent along the top and one from the parent along the side. In this case, all offspring have the same genotype and phenotype. The order of the letters doesn’t make a difference in the phenotype (aA is the same as Aa) but the capital letter is usually written before the lowercase one. These offspring are said to be heterozygous, meaning that they have two different alleles for pea color.
Despite the fact that both alleles are present in the offspring, the traits did not blend together to result in yellowish-green peas. Instead, only one phenotype was visible and all peas were yellow. Because of this, the yellow pea phenotype is said to be dominant, meaning that it is visible in the heterozygous individual. The letters in the middle show you all possible combinations of alleles that can happen from mating these two genotypes.

11. Now we see how it was possible for the green pea phenotype to skip a generation. The green pea allele was present in the F1 generation, but the phenotype was hidden by the yellow pea allele. The green pea phenotype is said to be recessive, meaning that it is only visible in the homozygous individual when the yellow allele is not present. In the F2 generation, only 1 of the 4 boxes produced green peas. In other words, 25% of the offspring had green peas. This number tells you the probability, or likelihood, that an offspring will produce green or yellow peas.

13. Questions???