1. Mendel’s Pea Plant Experiments
Mendelian Genetics
5/6/2018
Mendel’s Pea Plant Experiments

2. Gregor Johann Mendel Austrian monk, mathematician by trade
Mendelian Genetics
5/6/2018
Gregor Johann Mendel
Austrian monk, mathematician by trade
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
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"

3. Mendelian Genetics
5/6/2018
Genetic Terminology
Trait - any characteristic that can be passed from parent to offspring by genes(DNA) and their alleles(specific code sequences)
Heredity - passing of traits from parent to offspring
Genetics - study of heredity

4. Mendel’s Experimental Methods
Mendelian Genetics
5/6/2018
Mendel’s Experimental Methods
Mendel hand-pollinated flowers using a paintbrush
He snipped the stamens to prevent self-pollination
Covered each flower with a cloth bag
He traced 8 traits through the several generations
Ultimately he produced pure strains for each

5. Eight Pea Plant Traits GENE ALLELES GENE ALLELES Mendelian Genetics
5/6/2018
Eight Pea Plant Traits
GENE
ALLELES
GENE
ALLELES

6. Mendel’s Flowers Mendel’s questions:
If traits are known, can the inheritance of the traits in offspring be predicted?
What is the ‘mechanism’ for inheritance?
With his pure strains Mendel began systematically crossing plants, observing one trait at a time:
Monohybrid Crosses = 1 gene and its 2 alleles
He let the plants self-pollinate during these experiments
He observed the offspring produced for each trait, in each generation, for any patterns that appeared.

7. First filial generation of offspring
PURE STRAINS
WHY no white?
What happened to the
white trait?
First filial generation
of offspring
Second filial generation
White trait reappeared
in this generation,
so there must be some
‘factor’ in the purple
flower that masked it

8. Mendelian Genetics
5/6/2018
Mendel’s Conclusions
Dominant – trait that was expressed if present; represented by a capital letter (R)
Recessive – trait that is expresses only if the dominant is not present; represented by a lowercase letter (r)
Factors: sequence of DNA that codes for a trait, today we know those are the GENES
Alleles –variant(protein code) of a gene (dominant and/or recessive)
Ex: Trait(Gene)=Flower Color
Alleles=Purple/White
Regardless of the trait, results were the same and could be predicted in future generations…Mendel developed his first law of genetics;
The Law of Dominance
Gene Flower Color
Maternal
Chromosome
Paternal
Chromosome

9. Mendelian Genetics
5/6/2018
Law of Dominance
In a cross of parents(P) that are pure for contrasting traits, only one form of the trait will appear in the next generation(F1).
All the offspring will be heterozygous and express only the dominant trait.
RR x rr yields all Rr

10. Let’s see how it works, by adding the allele notations…RR rr Rr
Rr x Rr Rr rr RR Rr

11. GENOTYPEs Possible allele combinations for a trait
Mendelian Genetics
5/6/2018
GENOTYPEs
Possible allele combinations for a trait
Homozygous – allele combination involving two of the same alleles; can be either
Homozygous dominant: RR
Homozygous recessive: rr
Heterozygous – allele combination of one dominant & one recessive allele 
Heterozygous: Rr

12. PHENOTYPE the physical features resulting from the genotype; am I…
Phenotype also refers to your chemical features as well; enzymes and functional proteins, like hemoglobin, are also determined by genes and allele combinations
PURPLE
or, am I
WHITE

13. Genotype & Phenotype in Seed Color
Mendelian Genetics
5/6/2018
Genotype & Phenotype in Seed Color
Genotype of alleles: R = yellow seed r = green seed
In the F2
The possible combinations are:
Genotypes RR Rr rr
Phenotypes YELLOW YELLOW GREEN

14. Mendelian Genetics
5/6/2018
Punnett Squares
Diagram that is used to predict an outcome of a particular cross or breeding experiment
Illustrate Mendel’s Second Law of Genetics:
Law of Segregation

15. RR rr Rr RR Rr rr RR Rr Rr rr 1 2 3 4 5 6 Homozygous Dominant Parents
Recessive Parents 1 2
HDP X HRP P1 3 R R r r R R RR rr Rr R r r R r r
G: 4: Ph: 4:4
G: 4: Ph: 4:4
G: 4: Ph: 4:4
Heterozygous
Parents F2 4 5
HDP X Hetero 6
HRP X Hetero R r R R r r RR Rr rr RR Rr Rr rr R R R r r r
G: 1:2:1 Ph: 3:1
LOUNGE CHAIR
G: 2: Ph: 4:4
G: 2: Ph: 2:4

16. RR rr Rr RR Rr rr RR Rr Rr rr 1 2 3 4 5 6 Homozygous Dominant Parents
Recessive Parents 2
HDP X HRP P1 3 R R r r R R RR rr Rr R r r R r r
G: 4: Ph: 4:4
G: 4: Ph: 4:4
G: 4: Ph: 4:4
Heterozygous
Parents F2 4 5
HDP X Hetero 6
HRP X Hetero R r R R r r RR Rr rr RR Rr Rr rr R R R r r r
G: 1:2:1 Ph: 3:1
G: 2: Ph: 4:4
G: 2: Ph: 2:4

21. Predictable Generations
Mendelian Genetics
5/6/2018
Predictable Generations
Cross 2 Pure Plants TT x tt
Results in all Hybrids Tt
Cross 2 Hybrids get 3 Tall & 1 Short TT,Tt,Tt,tt