1. Genetics Unit 1

2. I. Background Stuff
Meiosis and fertilization pass the genetic code from parents to offspring
The genetic code is found in genes of chromosomes (DNA)
Heredity and the environment are the 2 factors that create an individual. You can control your environment but not your heredity

3. II. Gregor Mendel What is Genetics? - The study of heredity
What is heredity?
- Passing of traits from parents to offspring.
Father of Modern Genetics
Mendel was a monk
Studied pea plants

4. A. Peas
Why peas?
- Cheap, easy to grow, could self-pollinate, didn’t take much room, you can eat them, 7 black and white contrasting traits
Look at the 7 contrasting traits on page 215
Allele – contrasting forms of a trait
Phenotype – physical traits / green peas, purple flowers, round seeds are all phenotypes

5. III. Mendel’s Experiment
We will use a tall and a short pea plant for our example

6. A. Step 1
He “created” a pure-bred tall and a pure-bred short pea plant.
He did this by taking a tall plant and breeding it to itself and seeing if it had any short offspring. If it did he knew it was not pure-bred.

7. B. Step 2
He crossed a pure tall Pea plant with a pure short pea plant.
This is called the P generation / P stands for parental not Pea
What did he get?
He did not get medium because they do not exist. He did not get some tall and some short.
He got all tall / The offspring of the P generation is called the F1 generation.

8. C. Step 3 Mendel wondered what happened to the short allele.
He crossed two F1 generation plants.
What did he get?
He got 3 tall plants to every short plant or a 3tall:1short ratio
This is known as the F2 generation

9. IV. Mendel’s 4 Hypotheses
Mendel developed 4 hypotheses from his research which have been universally proven so they are really laws.

10. A. Genes occur in pairs
Mendel stated that you get one gene from mom and one from dad
So each phenotype is controlled by two genes, one from each parent
Genotype – the genetic makeup of an organism / the two genes you receive from your parents

11. B. Principle of Dominance and Recessive
One gene may mask the effects of the other.
The one that does the masking is the dominant trait / capital letter
The masked trait is recessive / lowercase letter
TT – Tall Pea Plant / Homozygous Dominant
tt – Short Pea Plant / Homozygous Recessive
Tt – Tall Pea Plant / Heterozyous

12. C. Principle of Segregation
Genes separate individually in meiosis
If one parent is Tt then half of the gametes will be T and the other half will be t

13. D. Principle of Independent Assortment
Traits are not linked or attached
Just because you are a tall pea plant does not mean you will have purple flowers.
Just because you have blond hair does not mean you will have blue eyes.

14. V. Predicting the Results of Genetic Crosses (Mating)

15. A. Basic Info
When Mendel crossed his F2 generation and saw a 3:1 ratio, the only pea’s genotypes he knew were the short ones (tt)
The tall ones could have been TT or Tt
R.C. Punnett created a system to determine the probable outcome of the cross.
Probability - # of one outcome / # possible outcomes
Everyone flip a penny 50 times and get the class average of heads vs. tails

16. A. Basic Info Continued What is the predicted ratio of heads to tails?
What did the class get? Is that wrong?

17. B. Monohybrid Cross
A cross between two individuals looking at 1 pair of triats (tall vs short)
Use a Punnett Square to show TT x tt and give the genotypic and phenotypic percents and ratios
Each box represents a possible offspring
Do the same with your F1, Tt x Tt