Introduction to Genetics

1. Introduction to Genetics

2. Learning Goal 4:Students will be able to explain the basic principles of heredity…- distinguish between dominant and recessive traits- use human examples- use Punnett squares 4= I know it & can teach it! 3= I know it 2= I know some of it 1= I know a little of it 0= What?

3. Gregor Mendel • He was an Austrian monk! • 1st person to study heredity • He was able to predict how traits are transferred from one generation to the next • Studied garden peas • He would transfer pollen from one plant to another plant with different traits • Controlled Experiment: only studied one trait at a time! (what a fantastic scientist!!)

4. The Pea Plants • Mendel studied several traits

5. Mendel crossed a tall (over 6 ft) pea plant with a short (less than 2 ft) pea plant RESULT: All tall plants Then he crossed two of the tall plants RESULT: 3 tall plants, 1 short plant His First Experiment HOW COULD THIS BE????

6. Let’s Take a Look…but first… some definitions! • Allele: gene form for each variation of a trait (ex. Gene for short plants (t); gene for tall plants (T) • Genotype: the gene combination of an organism (ex: Tt) – the capital/lowercase letter is extremely important! • Phenotype: the way an organism looks and behaves (ex: tall plants)

7. And a couple more… • Dominant: visible, observable trait of an organism that masks a recessive form of the trait. This trait is expressed ANYTIME the dominant allele is present. Expressed with a capital letter. • Recessive: a hidden trait of an organism that is masked by a dominant trait. This trait is only expressed if both alleles are recessive. Expressed with a lowercase letter

8. And two more… • Heterozygous: different alleles: Tt HYBRID • Homozygous: same alleles: TT or tt PURE BRED No more definitions… I promise… well… at least for a couple more slides!

9. Ok… back to those pea plants! One tall plant (TT) was bred with one short plant (tt). The result was 4 tall plants. Let’s look at a Punnett Square: (a tool used to calculate the probability of offspring outcomes) T T Plant One  Plant Two t t TtTt TtTt

10. T T Plant One  Plant Two t t TtTt TtTt The genotypes in the boxes are the possible offspring of the two plants. Since each has the dominant allele (T) all the plants will be TALL. The PHENOTYPE would be TALL

11. Let’s take it one step further! Let’s cross two of the offspring from the first cross (remember, they were all Tt) T t Plant One  Plant Two T t TTTt Tttt

12. What is the phenotype of each plant??? TALL! TALL! T t Plant One  Plant Two T t TT Tt Tt tt TALL! SHORT!

13. Let’s take a more in depth look at genotype & phenotype • Genotype: Tt, TT, tt • Phenotype: Tall, Tall, Short

14. Genotype: GG Gg gg Phenotype: Green Green Blue What if…. G= green, g= blue

15. Creating your own punnett square What are the possible offspring if you cross a short tailed cat (heterozygous- Ss) with a long tailed cat (homozygous – ss)? Short tails are dominant. S s Cat One  Cat Two s s Ssss Ssss

16. S s Cat One  Cat Two s s Ssss Ssss Possible offspring: Ss (short tail) or ss (long tail) What percent chance is there, if the cats produce ONE kitten, that it will have a short tail? 50% - a 2 out of 4 chance!

17. Try another… What are the possible offspring if you cross two 2-eyed monsters (heterozygous – Ee)? E= 2 eyes, e = 3 eyes E e Monster One  E e EEEe Eeee Monster Two

18. E e Monster One  E e EEEe Eeee Monster Two EE = two eyes Ee, Ee = two eyes ee = three eyes