1. Mendel’s Law of Heredity

2. Starter

3. Objectives Define a trait and what codes for it.
Describe Mendel’s first experiment and his conclusion

4. Review Match the following words to the picture. Homologous
chromosomes
(Tetrad)
Sister
Chromatids
Chromatin
Chromosome

5. Review Where in the cell are chromosomes found?
In the nucleus
What types of cells are you making in meiosis?
Sex cells: egg and sperm

6. Gregor Mendel Studied genetics
1st to succeed in predicting how traits are transferred from 1 generation to the next
Used pea plants in experiments
Reproduces sexually

7. Biology, 9th ed,Sylvia Mader
Chapter 11
Mendel’s Experiments
Mendel performed cross-breeding experiments
Used “true-breeding” plants
Chose varieties that differed in only one trait (monohybrid cross)
A true-breeding individual is pure for a certain trait. He comes after several generations having the same trait
Mendelian Inheritance

8. Monohybrid cross
Tested one trait
Height: tall and short

9. P1 (Parental generation)
Tall Plant X
Short Plant

10. Discuss with a partner if the offspring will be tall, short, or both.

11. F1 (First) Generation
All tall

12. Biology, 9th ed,Sylvia Mader
Chapter 11
Characteristics
Trait
*Dominant
*Recessive
Stem length
Tall
Short
Pod shape
Inflated
Constricted
Seed shape
Round
Wrinkled
Seed color
Yellow
Green
Flower position
Axial
Terminal
Flower color
Purple
White
Pod color
Green
Yellow
Mendelian Inheritance

13. Mendel called the trait that appeared the dominant trait
Mendel called the trait that appeared the dominant trait. The trait that seemed to fade into the background was called the recessive trait.

17. You should see a 2

18. You should see a 5

19. Everyone should have seen a 16

20. You should see a 42

21. You should see a 7

22. You should see a 29

23. You should see a 6

24. You should see a 57

25. You should see a 10

26. Normal colour vision will see a 5. An individual with Red/Green
(the most common)
colour blindness will see a 2.

27. Objectives Describe Mendel’s second experiment and his conclusion
Perform a simple cross using a punnet square

28. What did Mendel conclude after his first experiment?

29. Crossed the F1 generation with itself
Tall Plant X
Tall Plant

30. Discuss with a partner if the offspring will be tall, short, or both.

31. F2 (Second) Generation
3 tall: 1 short

34. After his observations, Mendel knew that there must be two sets of instructions for each characteristic. There was no other way to explain it.
This idea was a long time before the discovery of DNA
He didn’t even have a microscope!!

35. His Conclusion
Each organism has 2 factors (genes) that control each of its traits
Different forms of a gene= alleles
Example the plant has 1 allele for tall and 1 for short
Where do the
alleles come from?
1 from mother,
1 from father
Tall ♀
Same chromosome with different alleles ♂
Short

36. Put the words into the write column:
Brown eye color
height
Eye color
Blond hair
hair color
short
Black hair
Round nose
Nose shape
Alleles (specific)
Genes (general)

37. Dominant vs. Recessive Observed trait (always wins!)
Use a capital letter
Trait is not seen (masked)
Use a lowercase letter
Example for the trait HEIGHT (T)
T = Tall
t = Short
Dominant
Recessive
Example 2 for the trait CURLY HAIR (C)
C = Curly hair
c = straight hair
Dominant
Recessive

38. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Monohybrid Cross done by Mendel
Chapter 11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Allele Key
Phenotypic Ratio T =
tall plant 3
tall t =
short plant 1
short TT tt
Mendelian Inheritance

39. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Monohybrid Cross done by Mendel
Chapter 11
Slide #39
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Allele Key
Phenotypic Ratio T =
tall plant 3
tall
P generation t =
short plant 1
short TT tt 39

40. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Chapter 11
Slide #40
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Allele Key
Phenotypic Ratio
P generation T =
tall plant 3
tall t =
short plant 1
short TT tt
P gametes T t 40

41. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Monohybrid Cross done by Mendel
Chapter 11
Slide #41
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Allele Key
Phenotypic Ratio
P generation T =
tall plant 3
tall t =
short plant 1
short TT tt
P gametes T t tt
F1 generation Tt 41

42. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Chapter 11
Slide #42
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Allele Key
Phenotypic Ratio
P generation TT tt T =
tall plant 3
tall t =
short plant 1
short
P gametes T t
F1 generation Tt
eggs
F1 gametes T t T
sperm t 42

43. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Monohybrid Cross done by Mendel
Chapter 11
Slide #43
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
Allele Key
Phenotypic Ratio TT tt T =
tall plant 3
tall t =
short plant 1
short
P gametes T t
F1 generation Tt
eggs
F1 gametes T t T TT
sperm t 43

44. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Chapter 11
Slide #44
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
F1 generation
Allele key
Phenotypic Ratio TT tt T =
tall plant 3
tall t =
short plant 1
short
P gametes T t
F1 generation Tt
eggs
F1 gametes T t T TT Tt
sperm t 44

45. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Monohybrid Cross done by Mendel
Chapter 11
Slide #45
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
Allele Key
Phenotypic Ratio TT tt T =
tall plant 3
tall t =
short plant 1
short
P gametes T t
F1 generation Tt
eggs
F1 gametes T t T TT Tt
sperm t Tt 45

46. Monohybrid Cross done by Mendel
Biology, 9th ed,Sylvia Mader
Chapter 11
Slide #46
Mendelian Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation TT tt
P gametes T t
F1 generation Tt
eggs
F1 gametes T t T
sperm TT Tt
F2 generation t Tt tt
Offspring
Allele Key
Phenotypic Ratio T =
tall plant 46 3
tall t =
short plant 1
short

47. P1 (Parental generation)TT tt
Tall Plant X
Short Plant
Is t dominant or
recessive? t T
Is T dominant or
recessive?
Recessive
Dominant Tt
Is this tall or short?
Tall

48. Genotype (gene combination)
Phenotype (looks and behavior)
Homozygous (same alleles)
TT= homozygous dominant
Tall
tt= homozygous recessive
Short
Heterozygous (different alleles) Tt

49. Tt Tt Tt Tt TT tt F1 (First) Generation X Law of segregation
Heterozygous
Heterozygous Tt Tt X
Law of
segregation
Homozygous
Heterozygous
Heterozygous
Homozygous Tt Tt TT tt

50. Punnett Squares!

51. Step 1: Read the problem carefully.
Problem: In pea plants, tall is dominant to short. Mendel sprinkled the pollen of a homozygous dominant plant on the pistil of a heterozygous plant. What were the phenotypes of the offspring.

52. Step 2: Make a key that lists the traits (alleles) and their symbols.
Choose a letter: T
What trait is dominant?
T = Tall
What trait is recessive?
t = short

53. Step 3: Show the genotypes of the parents you are crossing.
Is the father (pollen) homozygous dominant, homozygous recessive, or heterozygous? TT
Is the mother (pistol) homozygous dominant, homozygous recessive, or heterozygous? Tt
Thus, you will get TT x Tt

54. Step 4: Draw a punnett square with 4 boxes for a monohybrid cross or 16 boxes for a dihybrid cross.
Are we testing 1 trait or 2 traits in the problem?
1 trait
Dihybrid (2 traits)
Monohybrid (1 trait)

55. Step 5: Figure out what types of gametes can be formed by the female and write them on the top side of the punnett square inside circles (to represent eggs).
Problem: genotype of female plant is Tt so gametes can be T or t T t

56. Step 6: Figure out what types of gametes can be formed by the male and write them on the left side of the punnett sqaure inside circles with tails (to represent sperm/ pollen)
Problem: genotype of male plant is TT so gametes can only be T. T t T T

57. Step 7: Fill in each box of the punnett sqaure which represent the zygotes or offspring of the parents. T t T TT Tt Tt TT T

58. Step 8: Determine the genotypic ratio of the offspring.
What are the allele pairs?
TT and Tt
Determine the ratio.
Genotypic ratio = 2TT:2Tt = TT:Tt = 1:1

59. Step 9: Determine the phenotypic ratio of the offspring.
Look at the genotypes of the offspring:
2TT and 2 Tt
Phenotypic ratio = all tall

60. Step 10: Make sure you answered any specific questions asked in the problem and box in your final answer.
Problem: What were the phenotypes of the offspring?
All Tall

61. Practice #1: Snow White loves her black hair but she married Prince Charming who has brown hair. Black is dominant to brown. If Snow White is heterozygous and Prince Charming is homozygous, what is the probability that they will have children with black hair?

62. Problem #2: The Transformer Bumblebee falls in love with a Lexus IS
Problem #2: The Transformer Bumblebee falls in love with a Lexus IS. The ability to transform is recessive. If Bumblebee and the homozygous dominant Lexus have gobots, what is the probability that their kids will be able to transform?

63. Problem #3: Hitchiker’s thumb is dominant
Problem #3: Hitchiker’s thumb is dominant. Shrek has hitchhiker’s thumb and Fiona does not. If 2 of their children have hitchiker’s thumb and 2 do not, then is Shrek homozygous or heterozygous for the trait?