1. Genetics Experiments With Pea Plants
Gregor Mendel
Genetics Experiments
With Pea Plants

2. Mendel Noticed Pea Plants varied by:
height, color of flowers, position of
flowers, seed color, seed shape,
pod color, pod shape

3. Mendel Hypothesized

4. Mendel Hypothesized
Variations in pea plant appearance was due to something (some information) passed along during reproduction by the parent plants.

5. Mendel’s Experimental Design

6. Mendel’s Experimental Design
Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short

7. Mendel’s Experimental Design
Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short
Mendel crossed one true-breeding variety with the alternate true-breeding variety, e.g. tall x short

8. P1 Tall X Short

9. P1 Tall X Short
F1 All Tall

10. P1 Tall X Short
F1 All Tall
F2 3/4 Tall 1/4 Short

11. Mendel Hypothesized
That something was passed from parents to offspring to determine height; he called this an allele

12. P1 Tall X Short
T t
F1 All Tall T
F2 3/4 Tall 1/4 Short

13. Mendel Hypothesized
That something was passed from parents to offspring to determine height; he called this an allele
Further, since the t allele was “hidden” in the F1, but reappeared in the F2, plants must have a pair of alleles for each trait.

14. P1 Tall X Short
TT tt
F1 All Tall Tt
F2 3/4 Tall 1/4 Short
T? tt

15. When an organism had a pair of alleles the same, e. g
When an organism had a pair of alleles the same, e.g. TT or tt, he called this homozygous
When an organism had an unlike pair of alleles, e.g. Tt, he called this heterozygous
These terms refer to an organism’s genotype
The appearance of the organism he called it’s phenotype

16. Practice Vocab Ex. Plant Height Genotype Phenotype Pure or Hybrid
Homozygous/
Heterozygous

17. More practice Ex. Flower color Genotype Phenotype Pure or Hybrid
Homozygous/
Heterozygous

18. Mendel proposed several principles regarding his findings
If an organism is heterozygous and only one phenotype appears, this is the dominant phenotype, the alternate is the recessive phenotype
When an organism reproduces, allele pairs must segregate and only one member of each allele pair is passed along to the next generation.

19. Solving Genetic Problems
T T
t t t T T t
T X t = T t F1

20. Punnett Square

21. TT X tt
t t
Genotype
4/4- Tt
Phenotype
4/4- Tall
Tt Tt
Tt Tt T

22. Practice Space

23. Test Cross What is the genotype of a short pea plant?______
What is the genotype of a tall pea plant?_____ or _____
Mendel developed a way of testing whether the tall plant is homozygous or heterozygous. It was the test cross

24. Test Cross problem
T_ X tt

25. Independent Assortment
The inheritance of any characteristic is independent of the inheritance of any other characteristic.
Ex. The inheritance of height is independent from pea color.
Mendel provided evidence for this through dihybrid crosses.

26. Dihybrid Cross TtPp X TtPp
To solve this problem you can use a 16 block punnett square or the Forkline method.

27. 16 Block Punnett Square

28. Fork Line Method

29. Ex. TtPp X TtPp

30. Practice with Fork Line Method

31. Practicing Punnett Squares

32. Inheritance patterns that Mendel did not know about
Incomplete dominance
Codominance
Multiple alleles
Polygenic Inheritence
Sex Linkage

33. Incomplete Dominance
Incomplete dominance does not involve an allele that masks recessive allele. Instead there is a blending of the two alleles.
Ex. Red flower X White flower =Pink
Cross Two Pink flowering plants

34. Example
Cross a two pink flowering plants
RW X RW

35. Codominance
Codominance does not involve an allele that masks recessive allele. Instead both alleles show in the phenotype
Ex. Brown horse X White horse =Spotted
Cross a brown horse with a spotted horse

36. Codominance Exmple
Cross a brown horse with a spotted horse.
BB X BW

37. Multiple Alleles
Some phenotypes can be determined by more than two alleles.
Ex. ABO Blood type
Genotypes Phenotypes
AA A Blood Type
AO A Blood Type
BB B Blood Type
BO B Blood Type
OO O Blood Type
AB AB Blood Type

38. Blood Type Problems
Cross a heterozygous A blood type with a heterozygous B blood type
iAiO X iBiO

39. Polygenic Inheritance
The inheritance of some characteristics are determined by more than two alleles.
Ex. Skin color, eye color, height, and noses. Phenotypes of polygenic inheritance are a result of the blending of many genes.

40. Sex Linkage Who determines the sex of the baby?
How would a gene found on the X chromosome be inherited and expressed differently in males vs. females?

41. Sex Inheritance
X Y X
XX XY
XX XY

42. Sex Linked Problems X-Linked
Color Blindness is carried on the X Chromosomes. It is recessive.
What are all of the different possible combinations of genotypes an individual could have?

43. Sex Linkage Problem
Cross a Colorblind male with a woman who is a carrier for colorblindness.
XcXC X XcY

44. Are you color blind? Lets find out together

45. Practice Sex Linkage Problems