1. Mendel’s Laws of Heredity

3. Gregor Mendel
Austrian monk who worked with garden peas
Did the first important studies of heredity – passing of characteristics from parent to offpring.

4. Mendel was the first to predict what traits would be passed from one generation to the next.
Trait: Inherited characteristics
We now know that traits are controlled by genes.

5. Most genes have two different forms or alleles.
Ex. Gene for pea shape has 2 possible alleles: round (R) or wrinkled (r)

6. Mendel also determined that:
Some alleles are dominant and others are recessive. (Principle of Dominance)
If you have a dominant allele for a trait you will always express that form.

7. Dominant alleles shown with capital letters. (Ex. D, R, S)
Recessive alleles shown with lowercase letters. (Ex. d,r,s)

8. An organism is homozygous for a trait if the two alleles are the same.
Ex. TT or tt
Heterozygous – the two alleles are different
Ex. Tt, Ss, Cc

9. Test Yourself
Is it homozygous or heterozygous?
Answers RR Tt Ff QQ

10. Test Yourself Homozygous Heterozygous RR Tt Ff QQ
Is it homozygous or heterozygous?
Answers RR Tt Ff QQ
Homozygous
Heterozygous

11. Homozygous dominant = DD
Homozygous recessive = dd
Heterozygous = Dd

12. Test Yourself
Is it dominant or recessive? Hh rr GG

13. Test Yourself Hh rr GG Dominant (heterozygous) Homozygous recessive
Is it dominant or recessive?
Answers Hh rr GG
Dominant (heterozygous)
Homozygous recessive
Homozygous dominant

14. Other Common Genetic Terms:
Phenotype – physical characteristics
Ex. Tall plants, green eyes
Genotype – describes genetic makeup.
Ex. TT, Tt, or tt

15. Example Tall plants are dominant over short plants.
What are the phenotypes?
TT___tall____
Tt___tall_____
tt___short______
What are the genotypes?
Tall___TT or Tt____
Short___tt____

16. Your turn In humans, brown eyes are dominant over green eyes.
What are the possible phenotypes?
BB_______
Bb_______
bb_______
What are the possible genotypes?
Brown_______
Blue________

17. Check yourself! In humans, brown eyes are dominant over green eyes.
What are the possible phenotypes?
BB___brown____
Bb__brown_____
bb___blue____
What are the possible genotypes?
Brown___BB or Bb____
Blue___bb_____

18. Geneticists use probability to predict the phenotypes and genotypes of offspring

19. Punnett Squares
Grids that can be used to predict the possible gene combinations of offspring
It shows probabilities of each genotype occuring not the actual results.