1. Mendelian Genetics
11/7/2018
Mendelelian Genetics

2. Responsible for the Laws governing Inheritance of Traits
Mendelian Genetics
11/7/2018
Gregor Mendel ( )
Responsible for the Laws governing Inheritance of Traits

3. Gregor Johann Mendel Austrian monk
Mendelian Genetics
11/7/2018
Gregor Johann Mendel
Austrian monk
Studied the inheritance of traits in pea plants
Developed the laws of inheritance
Mendel's work was not recognized until the turn of the 20th century

4. Mendelian Genetics
11/7/2018
Gregor Johann Mendel
Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants
He found that the plants' offspring retained traits of the parents
Called the “Father of Genetics"

5. Site of Gregor Mendel’s experimental garden in the Czech Republic
Mendelian Genetics
11/7/2018
Site of Gregor Mendel’s experimental garden in the Czech Republic
Fig. 5.co

6. Particulate Inheritance
Mendelian Genetics
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Particulate Inheritance
Mendel stated that physical traits are inherited as “particles”
Mendel did not know that the “particles” were actually Chromosomes & DNA

7. Mendelian Genetics
11/7/2018
Genetic Terminology
Trait - any characteristic that can be passed from parent to offspring
Heredity - passing of traits from parent to offspring
Genetics - study of heredity

8. Types of Genetic Crosses
Mendelian Genetics
11/7/2018
Types of Genetic Crosses
Monohybrid cross - cross involving a single trait e.g. flower color
Dihybrid cross - cross involving two traits e.g. flower color & plant height

9. Punnett Square Used to help solve genetics problems Mendelian Genetics
11/7/2018
Punnett Square
Used to help solve genetics problems

10. Mendelian Genetics
11/7/2018

11. Designer “Genes” Alleles - two forms of a gene (dominant & recessive)
Mendelian Genetics
11/7/2018
Designer “Genes”
Alleles - two forms of a gene (dominant & recessive)
Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)
Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

12. Mendelian Genetics
11/7/2018
More Terminology
Genotype - gene combination for a trait (e.g. RR, Rr, rr)
Phenotype - the physical feature resulting from a genotype (e.g. red, white)

13. Genotype & Phenotype in Flowers
Mendelian Genetics
11/7/2018
Genotype & Phenotype in Flowers
Genotype of alleles: R = red flower r = yellow flower
All genes occur in pairs, so 2 alleles affect a characteristic
Possible combinations are:
Genotypes RR Rr rr
Phenotypes RED RED YELLOW

14. Mendelian Genetics
11/7/2018
Genotypes
Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure 
Heterozygous genotype - gene combination of one dominant & one recessive allele    (e.g. Rr); also called hybrid

15. Genes and Environment Determine Characteristics
Mendelian Genetics
11/7/2018
Genes and Environment Determine Characteristics

16. Mendel’s Pea Plant Experiments
Mendelian Genetics
11/7/2018
Mendel’s Pea Plant Experiments

17. Why peas, Pisum sativum? Can be grown in a small area
Mendelian Genetics
11/7/2018
Why peas, Pisum sativum?
Can be grown in a small area
Produce lots of offspring
Produce pure plants when allowed to self-pollinate several generations
Can be artificially cross-pollinated

18. Reproduction in Flowering Plants
Mendelian Genetics
11/7/2018
Reproduction in Flowering Plants
Pollen contains sperm
Produced by the stamen
Ovary contains eggs
Found inside the flower
Pollen carries sperm to the eggs for fertilization
Self-fertilization can occur in the same flower
Cross-fertilization can occur between flowers

19. Mendel’s Experimental Methods
Mendelian Genetics
11/7/2018
Mendel’s Experimental Methods
Mendel hand-pollinated flowers using a paintbrush
He could snip the stamens to prevent self-pollination
Covered each flower with a cloth bag
He traced traits through the several generations

20. Mendelian Genetics
11/7/2018
How Mendel Began
Mendel produced pure strains by allowing the plants to self-pollinate for several generations

21. Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r)
Mendelian Genetics
11/7/2018
Eight Pea Plant Traits
Seed shape --- Round (R) or Wrinkled (r)
Seed Color ---- Yellow (Y) or  Green (y)
Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color ---  Green (G) or Yellow (g)
Seed Coat Color ---Gray (G) or White (g)
Flower position---Axial (A) or Terminal (a)
Plant Height --- Tall (T) or Short (t)
Flower color --- Purple (P) or white (p)

22. Mendelian Genetics
11/7/2018

23. Mendelian Genetics
11/7/2018

24. Mendel’s Experimental Results
Mendelian Genetics
11/7/2018
Mendel’s Experimental Results

25. Did the observed ratio match the theoretical ratio?
Mendelian Genetics
11/7/2018
Did the observed ratio match the theoretical ratio?
The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled
Mendel’s observed ratio was 2.96:1
The discrepancy is due to statistical error
The larger the sample the more nearly the results approximate to the theoretical ratio

26. Mendelian Genetics
11/7/2018
Generation “Gap”
Parental P1 Generation = the parental generation in a breeding experiment.
F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation)
From breeding individuals from the P1 generation
F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation)
From breeding individuals from the F1 generation

27. Following the Generations
Mendelian Genetics
11/7/2018
Following the Generations
Cross 2 Pure Plants TT x tt
Results in all Hybrids Tt
Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt

28. Mendelian Genetics
11/7/2018
Monohybrid Crosses

29. P1 Monohybrid Cross r r Rr Rr R R Rr Rr Trait: Seed Shape
Mendelian Genetics
11/7/2018
P1 Monohybrid Cross
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x Wrinkled seeds
RR x rr
Genotype: Rr
Phenotype: Round
Genotypic Ratio: 100% Rr
Phenotypic Ratio: 100% round r r Rr Rr R R Rr Rr

30. P1 Monohybrid Cross Review
Mendelian Genetics
11/7/2018
P1 Monohybrid Cross Review
Homozygous dominant x Homozygous recessive
Offspring all Heterozygous (hybrids)
Offspring called F1 generation
Genotypic & Phenotypic ratio is ALL ALIKE

31. F1 Monohybrid Cross R r RR Rr R r Rr rr Trait: Seed Shape
Mendelian Genetics
11/7/2018
F1 Monohybrid Cross
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x Round seeds
Rr x Rr
G.Ratio: 1:2:1
RR:Rr:rr
P.Ratio: 3:1
round:wrinkled R r RR Rr R r Rr rr

32. F1 Monohybrid Cross Review
Mendelian Genetics
11/7/2018
F1 Monohybrid Cross Review
Heterozygous x heterozygous
Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr
Offspring called F2 generation
Genotypic ratio is 1:2:1
Phenotypic Ratio is 3:1

33. What Do the Peas Look Like?
Mendelian Genetics
11/7/2018
What Do the Peas Look Like?

34. Mendelian Genetics
11/7/2018
…And Now the Test Cross
In order to find the genotype of a dominant-showing trait, the organism must be crossed with a homozygous recessive organism.
There are two possible testcrosses: Homozygous dominant x homozygous recessive Heterozygous x Homozygous recessive

35. Test Cross (1st) r r Rr Rr R R Rr Rr Trait: Seed Shape
Mendelian Genetics
11/7/2018
Test Cross (1st)
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x wrinkled seeds
RR x rr
Genotype: RR, Rr
Phenotype: Round
Genotypic Ratio: 100% Rr
Phenotypic Ratio: 100% round r r Rr Rr R R Rr Rr

36. Test Cross (2nd) R r Rr rr r r Rr rr Trait: Seed Shape
Mendelian Genetics
11/7/2018
Test Cross (2nd)
Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Wrinkled seeds x Round seeds
rr x Rr R r
Genotype: Rr, rr
Phenotype: Round & Wrinkled
G. Ratio: 1:1
P.Ratio: 1:1 Rr rr r r Rr rr

37. Test Cross Results So, if Offspring are: 50% wrinkled rr 50% round Rr
Mendelian Genetics
11/7/2018
Test Cross Results
So, if Offspring are: 50% wrinkled rr 50% round Rr
Shows that unknown parent is Heterozygous Rr
But, if offspring are:
100% round Rr
Shows that unknown parent is
Homozygous dominant RR

38. A black male rabbit is mated with a brown female rabbit (bb)
A black male rabbit is mated with a brown female rabbit (bb). Their offspring are black and brown in a 1:1 ratio. Use a Punnett square to determine the genotype of the black male parent.

39. Mendelian Genetics
11/7/2018
Mendel’s Laws

40. Results of Monohybrid Crosses
Mendelian Genetics
11/7/2018
Results of Monohybrid Crosses
Inheritable factors or genes are responsible for all heritable characteristics
Phenotype is based on Genotype
Each trait is based on two genes, one from the mother and the other from the father
True-breeding individuals are homozygous ( both alleles) are the same

41. Law of Dominance One allele overshadows the other allele for a trait.
Mendelian Genetics
11/7/2018
Law of Dominance
One allele overshadows the other allele for a trait.
The allele that is overshadowed is called the recessive allele. The one that does the overshadowing is the dominant allele.

42. Mendelian Genetics
11/7/2018
Law of Dominance

43. Mendelian Genetics
11/7/2018
Law of Segregation
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.
Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

44. Applying the Law of Segregation
Mendelian Genetics
11/7/2018
Applying the Law of Segregation

45. Law of Independent Assortment
Mendelian Genetics
11/7/2018
Law of Independent Assortment
Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
This law is illustrated by the meiosis babies activity and dihybrid crosses.

46. Mendelian Genetics
11/7/2018
Dihybrid Cross
A breeding experiment that tracks the inheritance of two traits.
Mendel’s “Law of Independent Assortment”
a. Each pair of alleles segregates independently during gamete formation
b. Formula: 2n (n = # of heterozygotes)

47. Remember: 2n (n = # of heterozygotes)
Mendelian Genetics
11/7/2018
Question: How many gametes will be produced for the following allele arrangements?
Remember: 2n (n = # of heterozygotes)
1. RrYy
2. AaBbCCDd
3. MmNnOoPPQQRrssTtQq

48. Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry
Mendelian Genetics
11/7/2018
Answer:
1. RrYy: 2n = 22 = 4 gametes
RY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gametes
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCd
3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

49. All possible gamete combinations
Mendelian Genetics
11/7/2018
Dihybrid Cross
Traits: Seed shape & Seed color
Alleles: R round r wrinkled Y yellow y green
RrYy x RrYy
RY Ry rY ry
RY Ry rY ry
All possible gamete combinations

50. Mendelian Genetics
11/7/2018
Dihybrid Cross RY Ry rY ry RY Ry rY ry

51. Dihybrid Cross RY Ry rY ry Round/Yellow: 9 Round/green: 3
Mendelian Genetics
11/7/2018
Dihybrid Cross RY Ry rY ry
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy

52. Mendelian Genetics
11/7/2018
Dihybrid Cross
Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1
9:3:3:1

53. Practice:
Cross a pea plant with homozygous for round seeds and heterozygous for yellow seeds with a pea plant heterozygous for round seeds and homozygous for yellow seeds.

54. Practice RY Ry RY rY RRYY RRYy RRYY RRYy RrYY RrYy RrYy RrYY RRYY RRYy
Mendelian Genetics
11/7/2018
Practice RY Ry RY rY
RRYY
RRYy
RRYY
RRYy
RrYY
RrYy
RrYy
RrYY
RRYY
RRYy
RRYY
RRYy
RrYY
RrYy
RrYY
RrYy

55. Practice Results: Phenotypic Ratios: Round/yellow: 100%
Why different than the previous cross? (9:3:3:1)
Could this Punnett square be shortened?

56. Mendelian Genetics
11/7/2018
Test Cross
A mating between an individual of unknown genotype and a homozygous recessive individual.
Example: bbC__ x bbcc
BB = brown eyes
Bb = brown eyes
bb = blue eyes
CC = curly hair
Cc = curly hair
cc = straight hair bC
b___ bc

57. Test Cross Possible results: bC b___ bc bbCc C bC b___ bc bbCc bbcc or
Mendelian Genetics
11/7/2018
Test Cross
Possible results: bC
b___ bc
bbCc C bC
b___ bc
bbCc
bbcc or c

58. Summary of Mendel’s laws
Mendelian Genetics
11/7/2018
Summary of Mendel’s laws
LAW
PARENT CROSS
OFFSPRING
DOMINANCE
TT x tt tall x short
100% Tt tall
SEGREGATION
Tt x Tt tall x tall
75% tall 25% short
INDEPENDENT ASSORTMENT
RrGg x RrGg round & green x round & green
9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods