1. Mendelian Genetics

2. Gregor Mendel
Responsible for the laws governing inheritance of traits.

3. Gregor Mendel Austrian Monk
Studied the inheritance of traits in pea plants
Developed the Laws of Inheritance
Mendel’s work was not recognized until the early 20th century

4. Gregor 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
He is known as the “Father of Genetics”

5. Gregor’s Garden
The site of Mendel’s garden in the Czech Republic

6. Particulate Inheritance
Mendel stated that physical traits are inherited as “particles”
Mendel did not know that the “particles” were DNA and chromosomes.

7. Punnett Square
Used to help solve genetic problems.
Uses probability.

8. Punnett Square

9. Genotype and Phenotype
Genotype – gene combination for a trait
Ex. RR, Rr, rr
Phenotype – the physical feature resulting from the genotype
Ex. Red, pink, white

10. Genotype and Phenotype
Genotype of alleles:
R = red flower
r = yellow flower
All genes occur in pairs, so TWO alleles affect a characteristic
Possible combinations are:
Genotypes: RR Rr rr
Phenotypes: Red Red Yellow

11. Genotypes Homozygous Heterozygous
Gene combination involving two dominant or two recessive genes (ex. RR or rr)
Also called pure
Heterozygous
Gene combination of one dominant and one recessive allele (ex. Rr)
Also called hybrid

12. Genes AND Environment determine characteristics

13. Mendel’s Pea Plant Experiments

14. Why Peas? (Pisum sativum)
Can be grown in a small area.
Can produce a lot of offspring.
Will produce pure plants when allowed to self-pollinate over several generations.
Can also be artificially cross-pollinated.

15. Reproduction In Flowering Plants
Pollen contains sperm
Produced by the stamen
Carries sperm to the eggs for pollination
Ovary produces eggs
Found inside the flower
Self-pollination
Can occur within the same flower
Cross-pollination
Can occur between unrelated flowers

16. Mendel’s Experimental Methods
Mendel hand-pollinated flowers using a paintbrush
He could snip the stamens to prevent self-pollination.
He traced traits through several generations.

17. How Mendel Began
Mendel produced pure strains of pea plants by allowing the plants to self-pollinate over several generations.

18. 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)
Flower color – purple (P) or white (p)
Plant height – tall (T) or short (t)

19. Eight Pea Plant Traits

20. Eight Pea Plant Traits

21. Mendel’s Experimental Results

22. 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. This discrepancy is due to statistical error.
The larger the sample, the more nearly results reflect the theoretical ratios

23. Mendel’s Generations Parental Generation (P1)
The original (parental) generation in a breeding experiment.
First Filial Generation (F1)
The first generation of offspring in a breeding experiment.
From breeding individuals in the P1 generation.
Second Filial Generation (F2)
The second generation of offspring in a breeding experiment.
From breeding individuals in the F1 generation.

24. Following the Generations
Cross two pure plants.
TT x tt
Cross two hybrids
Get 3 tall : 1 short
TT, Tt, tt
Results in all Hybrids Tt

25. Monohybrid Crosses

26. P1 Monohybrid Cross RR x rr r r R Rr Rr R Rr Rr Trait : Seed Shape
Alleles : R – round, r – wrinkled
Cross : round seeds X wrinkled seeds
RR x rr r r
Genotype: Rr
Phenotype: Round
Genotypic Ratio: All alike
Phenotypic Ratio: All alike R Rr Rr R Rr Rr

27. P1 Monohybrid Cross Review
Homozygous dominant x homozygous recessive
Offspring all heterozygous (hybrids)
Offspring called F1 generation
Genotypic and phenotypic ratio is all alike.

28. F1 Monohybrid Cross Rr x Rr R r R RR Rr r Rr rr Trait : Seed Shape
Alleles : R – round, r – wrinkled
Cross : round seeds X round seeds
Rr x Rr R r
Genotype: RR, Rr, rr
Phenotype: Round & Wrinkled
Genotypic Ratio: 1 : 2 : 1
Phenotypic Ratio: 3 : 1 R RR Rr r Rr rr

29. F1 Monohybrid Cross 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

30. What do the peas look like?

31. Test Cross
Mendel then crossed a pure and a hybrid from his F2 generation.
This is known as an F2 or test cross
There are two possible test crosses
Homozygous dominant x hybrid
Homozygous recessive x hybrid

32. F2 Monohybrid Cross (1st)
Trait : Seed Shape
Alleles : R – round, r – wrinkled
Cross : round seeds X round seeds
RR x Rr R r
Genotype: RR, Rr
Phenotype: Round
Genotypic Ratio: 1 : 1
Phenotypic Ratio: All alike R RR Rr R RR Rr

33. F2 Monohybrid 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
Genotypic Ratio: 1 : 1
Phenotypic Ratio: 1 : 1 r Rr rr r Rr rr

34. F2 Monohybrid Cross Review
Homozygous x heterozygous (hybrid)
Offspring
50% homozygous – RR or rr
50% heterozygous – Rr
Phenotypic Ratio – 1 : 1
Genotypic Ratio – 1 : 1
Called a test cross because the offspring have the SAME genotype as parents.

35. Mendel’s Laws

36. 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 alleles, one from ma, the other from pa.
True breeding individuals are homozygous (both alleles are the same).

37. Law of Dominance
In a cross of parents that are PURE for CONSTRASTING TRAITS, only ONE FORM of the trait WILL APPEAR in the next generation.
All offspring will be HETEROZYGOUS and will EXPRESS only the DOMINANT TRAIT.
RR x rr yields all Rr

38. 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 offspring.

39. Law of Segregation

40. Law of Independent Assortment
Alleles for different traits are distributed to sex cells & offspring independently from one another.
Each pair of alleles segregates independently during gamete formation.
Formula = 2n (n = the # of heterozygotes)
This law can be illustrated using dihybrid crosses.

41. How many gametes will be produced for the following allele arrangements?
2n = (n = # of heterozygotes)
RrYy
AaBbCCDd
MmNnOoPPQQRrssTtUu

42. Answers: RrYy AaBbCCDd MmNnOoPPQQRrssTtUu
2n = 22 = 4 gamete combinations
RY Ry rY ry
AaBbCCDd
2n = 23 = 8 gamete combinations
ABCD ABCd AbCD AbCd aBCD aBCd abCD aBcD
MmNnOoPPQQRrssTtUu
2n = 26 = 64 gamete combinations

43. Dihybrid Crosses
A breeding experiment that tracks the inheritance of TWO different TRAITS.
Ex. Tail size and Fur Color

44. All possible gamete combinations
Dihybrid Crosses
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

45. Dihybrid Cross RY Ry rY ry RY Ry rY ry

46. Dihybrid Cross RY Ry rY ry RY Ry rY ry RRYY RRYy RrYY RrYy RRYy RRyy
Round /Yellow: 9
Round/Green: 3
Wrinkled/Yellow: 3
Wrinkled/Green: 1
Phenotypic Ratio—
9 : 3 : 3 : 1 Ry
RRYy
RRyy
RrYy
Rryy rY
RrYY
RrYy
rrYY
rrYy ry
RrYy
Rryy
rrYy
rryy

47. Dihybrid Cross Round/Yellow: 9 Round/Green: 3 Wrinkled/Yellow: 3
Wrinkled/Green: 1
9 : 3 : 3 : 1

48. Test Cross
A mating between an individual with unknown genotype and a homozygous recessive individual.
Ex. bbC_ x bbcc
BB = brown eyes
Bb = brown eyes
bb = blue eyes
CC = curly hair
Cc = curly hair
cc = straight hair bC
b___ bc

49. Test Cross Possible Results bC b___ bc bbCc C bC b___ bc bbCc bbcc or

50. Summary of Mendel’s Laws
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

51. Incomplete Dominance and Codominance

52. Incomplete Dominance
F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.
Ex. Snapdragons
Red (RR) White (rr) r r R R

53. Produces the F1 Generation
Incomplete Dominance r r
Produces the F1 Generation
All Rr = Pink
(heterozygous pink) R Rr Rr R Rr Rr

54. Incomplete Dominance

55. Codominance Two alleles are expressed in heterozygous individuals.
Ex. Blood Type
Type A = IAIA or IAi
Type B = IBIB or IBi
Type AB = IAIB
Type O = ii

56. Codominance IB IA i Example: 50% = IAIB 50% = IBi IAIB IBi IAIB IBi
homozygous male Type B x heterozygous female Type A
IBIB x IAi IB IA i
50% = IAIB
50% = IBi
IAIB
IBi
IAIB
IBi

57. Sex-Linked Traits
Traits (genes) located on the sex chromosomes (X and Y)
XX genotype for females
XY genotype for males
Many sex-linked traits are carried on the X chromosome.

58. Females can carry sex-linked genetic disorders.
Only females can be carriers of sex-linked disorders.
Males have an XY genotype.
A male who has a gene for a disorder located on the X chromosome will not have a second, normal allele to mask it.
Therefore, the males will display the disorder.
Females can be carriers because they have a normal allele that gives them a normal phenotype.

59. Sex-Linked Traits
The likelihood of inheriting a sex-linked disorder depends both on the sex of the child and on which parent carries the disorder-causing allele.
If only the mother has the allele, and is a carrier, a child has a 50% chance on inheriting the allele.

60. Sex Linked Traits Example: Hemophilia (blood clotting disorder)
Sex Chromosomes
XX chromosome - female
Xy chromosome - male
Blood Clotting
Gene

61. Sex-Linked Trait

62. Pedigrees
All your traits, blue eyes, blond hair, freckles, and every other aspect of your phenotype, are the result of the genes that you inherited from your parents.

63. Human genetics follows the patterns
The inheritance of many traits is very complex.
A single trait may be controlled by several genes that interact.
Ex. Height
Several genes affect a person’s height.
BUT, a person’s environment during growth and development plays a role in their final adult height.

64. Human Genetics Follows Patterns
Single-gene traits are very helpful in understanding human genetics.
Ex. Hairline
A widows peak is dominant, while a straight hairline is recessive.
Hairline inheritance follows dominant and recessive patterns.
Many genetic disorders (Huntington’s disease, hemophilia, Duchenne’s muscular dystophy) are caused by single genes that follow dominant and recessive patterns.
Much of what is known about human genetics comes from studying genetic disorders.

65. A pedigree is a chart for tracing genes in a family.
A pedigree chart can help trace the phenotypes and genotypes in a family to determine whether people carry recessive alleles.
When enough family phenotypes are known, genotypes can often be inferred.

66. A pedigree chart is for tracing genes in a family
Boxes represent Males
Circles represent Females
Shaded shapes means that a person shows the trait
Clear shapes (white shapes) means that a person does not show a trait.
A half-shaded/half white shape means that a person is a carrier.
Lines connect a person to his or her mate, and to their children.