1. Like humans, plants have genes, and different alleles exist for those genes.
Gene: Petal Color
Red allele
Yellow allele
Purple allele

2. This is a particular type of plant called a pea plant:
Pea plant flowers
Peas
Seeds of the pea plant

3. Allele 1 Allele 1 Allele 1 Gene Gene Gene Allele 2 Allele 2 Allele 2
Each pea plant gene has two alleles.
Allele 1
Allele 1
Allele 1
Allele 1
Gene
Gene
Gene
Gene
Flower Color
Flower Position
Seed Color
Seed Shape
Pod Shape
Pod Color
Plant Height
Purple
Purple
Axial
Yellow
Round
Inflated
Green
Tall
White
Terminal
Green
Wrinkled
Constricted
Yellow
Short
Allele 2
Allele 2
Allele 2
Allele 2

4. Like humans, plants pass their genes to the next generation by producing gametes.

5. As with us, plant gametes combine during fertilization
As with us, plant gametes combine during fertilization. Offspring receive two copies of every gene.
Purple
White
Purple
Purple
White
Purple

6. The difference is that flowering plants produce both male and female gametes.
(Polllen)
Eggs

7. Pollen
The male gametes of a plant. G P

8. Flowers can reproduce through self-pollination…

9. Or cross-pollination. C

10. Cross-pollination is usually facilitated by insects.

11. Only cross-pollination can produce hybrid offspring.
Self-pollination
Cross-pollination

12. Gregor Mendel, a 19th-century Austrian monk and scientist, used his knowledge of plant reproduction to create one of the first genetics experiments.

13. Gregor Mendel
An early plant geneticist who discovered the laws of inheritance. G L

14. Mendel knew nothing about DNA or genes (his experiment was conducted about the same time as the civil war.)

15. We did have microscopes, though, so we knew about gametes and fertilization.

16. Mendel set out to answer three questions about inheritance.

17. 1. Why do some allele blend, while others don’t?
BROWN
HAZEL

18. 2. Why do some alleles appear to skip a generation?

19. 3. Do alleles for different genes stay together?
Gene: Fur color
Gene: Fur pattern
Alleles: Brown, tan
Alleles: Solid, stripe
Tan, stripe
Brown, solid
Brown, stripe

20. To answer these questions, Mendel produced hybrids.
Flower Color
Flower Position
Seed Color
Seed Shape
Pod Shape
Pod Color
Plant Height
Purple
Purple
Axial
Yellow
Round
Inflated
Green
Tall
White
Terminal
Green
Wrinkled
Constricted
Yellow
Short

21. To make hybrids, Mendel had to ensure that his plants did not accidentally self-pollinate.
Self-pollination
Cross-pollination

22. To prevent self-pollination, Mendel removed the male parts of one flower and dusted it with pollen from another flower. S M F P F
Pollen transfer
Flower 1
Flower 2

23. Mendel began his experiment by crossing one tall pea plant and one short pea plant. He called these plants the P generation (parent generation).
T = Tall
t = short X
P generation

24. My parents were both tall! My parents were both short!
Remember that living things have 2 copies of every gene.
My parents were both tall!
My parents were both short! TT tt
T = Tall
t = short X
P generation

25. Mendel hypothesized that the tall and short alleles would blend in the hybrid offspring.?
T = Tall
t = short = X
P generation

26. F1 generation (hybrids)TT tt X
P generation
F1 generation (hybrids)

27. F1 generation (hybrids)
All of the F1 hybrids were tall; Mendel’s hypothesis was not supported. T H S TT tt X
P generation
F1 generation (hybrids)

28. F1 generation (hybrids)
Each of the F1 hybrids inherited one tall allele and one short allele. So why didn’t the alleles blend? TT Tt Tt Tt Tt tt X
P generation
F1 generation (hybrids)

29. Mendel concluded that some alleles are dominant, while others are recessive.

30. F1 generation (hybrids)
Dominant alleles are always expressed, even if only 1 copy is inherited. D E TT Tt Tt Tt Tt tt X
P generation
F1 generation (hybrids)

31. F1 generation (hybrids)
Recessive alleles are only expressed when 2 copies are inherited. R E TT Tt Tt Tt Tt tt X
P generation
F1 generation (hybrids)

32. Brown eyes (B) are dominant, while blue eyes (b) are recessive.BB Bb bb

33. The green eye allele (G) is somewhat recessive to brown, but dominant to blue.GG GB Gb

34. Dominant = more protein made
Blue allele
Brown allele
From Dad
From Mom

35. Dominant = more protein made
Green allele
Brown allele
From Dad
From Mom

36. PRINCIPLE OF DOMINANCE
1. Why do some allele blend, while others don’t?
PRINCIPLE OF DOMINANCE
BROWN
HAZEL

37. Mendel wanted to know what would happen if he cross-pollinated the F1 plants. He crossed two of the F1 hybrids and created an F2 generation. Tt Tt X F1
F2 generation

38. ¼ of the F2 plants were short.Tt Tt tt X F1
F2 generation

39. Why did shortness reappear in the F2 generation?

40. In order for 2 recessive alleles to pair up during fertilization, the allele for shortness (t) must somehow separate, or segregate, from the allele for tallness (T). T t T t

41. Segregation Bb Bb B b B b The separation of alleles when gametes form.

42. Why shortness reappeared in F2Tt Tt
F1 generation
Segregation T t T t
Gametes T t T t
Fertilization
F2 generation TT Tt Tt tt

43. TT Tt Tt tt
F2 generation

44. Because of segregation, 2 recessive alleles were able to pair up during fertilization to produce a short plant. S R F S Tt Tt
F1 generation
Segregation T t T t
Sex cells
Fertilization
F2 generation TT Tt Tt tt

45. PRINCIPLE OF SEGREGATION
2. Why do some alleles appear to skip a generation?
PRINCIPLE OF SEGREGATION

46. We can use Mendel’s principles of dominance and segregation to explain many phenomena in genetics.

47. Genetics Problem #1
The allele for brown eyes (B) is dominant, while the allele for blue eyes (b) is recessive.
What is the only possible allele combination for a blue-eyed person? bb
What are two possible allele combinations for a brown-eyed person? BB Bb

48. Brown = B (dominant); Blue = b (recessive)Bb Bb
Parents
Segregation
Gametes B b B b
Fertilization
Offspring BB Bb Bb bb

49. Brown = B (dominant); Blue = b (recessive)
34. Explain why the parents in this diagram have brown eyes, even though they both carry the allele for blue eyes.
35. Explain why bb is the only possible allele combination for a blue-eyed person.
36. Explain why two recessive alleles were able to pair up during fertilization to produce a blue-eyed baby.
37. The blue-eyed baby has a brown-eyed sister from the same parents. Explain how this is possible.
Dominant
One copy
Recessive
Two copies
Segregation
BB or Bb

50. Genetics Problem #2

51. Genetics Problem #2
The allele for dark skin (D) is dominant, while the allele for light skin (d) is recessive.
What is the only possible allele combination for a light-skinned person? dd
What are two possible allele combinations for a dark-skinned person? DD Dd

52. Dark = D (dominant); Light = d (recessive)
Parents Dd dd
Segregation
Gametes D d d d
Fertilization
Offspring Dd Dd dd dd

53. Brown = B (dominant); Blue = b (recessive)
34. Explain why the father in this diagram has dark skin, even though he carries the allele for light skin.
35. Explain why dd is the only possible allele combination for the mother.
36. Explain why two recessive alleles were able to pair up during fertilization to produce a light-skinned baby.
37. Explain why one of the sisters has dark skin.
Dominant
One copy
Recessive
Two copies
Segregation Dd