1. Genetics
A study of inheritance

2. Objectives Understand Phenotype Genotype Dominance Gene Segregation
Use a Punnett square to
Solve monohybrid crosses
Predict genotype ratio
Predict phenotype ratio

3. Gregor Mendel
Father of modern genetics

4. Gregor Mendel
Father of modern genetics
Researched with pea plants

5. Gregor Mendel Father of modern genetics Researched with pea plants
Developed ideas of dominance and trait segregation

6. Phenotype
Phenotype
Physical characteristics

7. Genotype Phenotype Genotype Physical characteristics
Genes we inherit from our parents

8. Phenotype
Notice the similarities:
Facial structure

9. Phenotype
Notice the similarities:
Facial structure
Eyes

10. Phenotype
Notice the similarities:
Facial structure
Eyes
Smile

11. Phenotype
Notice the similarities:
Facial structure
Eyes
Smile
Ears

12. Phenotype Notice the similarities: Facial structure Eyes Smile Ears
Nose

13. Phenotype Notice the similarities: Facial structure Eyes Smile Ears
Nose
Neck

14. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL

15. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW

16. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND

17. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY

18. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY
Pod shape - constricted or SMOOTH

19. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY
Pod shape - constricted or SMOOTH
Pod color - yellow or GREEN

20. Mendelian Genetics
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY
Pod shape - constricted or SMOOTH
Pod color - yellow or GREEN
Flower position - terminal or AXIAL

21. Mendelian Genetics We will work with the following three:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY
Pod shape - constricted or SMOOTH
Pod color - yellow or GREEN
Flower position - terminal or AXIAL

22. Predicting Inheritance
To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes.
UPPERCASE letters are used to represent dominant genes.
lowercase letters are used to represent recessive genes.

23. Predicting Inheritance
For example:
T = represents the gene for TALL in pea plants
t = represents the gene for short in pea plants
So:
TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive.
tt will result in a short plant.
Remember there are two genes for every trait! One from each parent.

24. Predicting Inheritance
For example:
T = represents the gene for TALL in pea plants
t = represents the gene for short in pea plants
So:
TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive.
tt will result in a short plant.
Remember there are two genes for every trait!
Mendels’ Principle of Dominance
Some genes (alleles) are dominant and others are recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene.

25. Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a short plant (tt).
Each plant will give only one of its’ two genes to the offspring or F1 generation.
TT x tt T T t t

26. Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a short plant (tt).
Each plant will give only one of its’ two genes to the offspring or F1 generation.
TT x tt
Mendels’ “Law” of Segregation
Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait. T T t t

27. Punnett Squares Tt The genes from one parent go here.
The genes from the other parent go here.

28. Punnett Squares T t Tt

29. Punnett Squares T t Tt

30. Punnett Squares T t Tt

31. Punnett Squares T t Tt

32. Punnett Squares T t Tt

33. Punnett Squares T t Tt
F1 generation

34. Interpreting the Results
The genotype for all the offspring is Tt.
The genotype ratio is:
Tt - 4/4
The phenotype for all the offspring is tall.
The phenotype ratio is:
tall - 4/4

35. Punnett Squares T t ??
Your Turn!!

36. Punnett Squares T t TT Tt tt
F2 generation

37. Punnett Squares T t TT Tt tt
Next, give the genotype and phenotype ratios of the offspring (F2 generation). T t TT Tt tt

38. Punnett Squares
Genotype ratio: TT - 1 T t TT Tt tt

39. Punnett Squares
Genotype ratio: TT - 1, Tt - 2 T t TT Tt tt

40. Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1 T t TT Tt tt

41. Punnett Squares T t TT Tt tt Genotype ratio: TT - 1, Tt - 2, tt - 1
Phenotype ratio: Tall - 3

42. Punnett Squares T t TT Tt tt Genotype ratio: TT - 1, Tt - 2, tt - 1
Phenotype ratio: Tall - 3, short - 1

43. Punnett Squares T t TT Tt tt
This is a monohybrid cross. We worked with only one trait. The height of the plant.

44. Punnett Squares T t TT Tt tt
This is a monohybrid cross. We worked with only one trait. The height of the plant.
two
Later we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape.