1. Mendelian Genetics
Biology 30

2. Gregor Mendel
Used pure-breeding (genetically identical) lines of garden peas
Lived
Father of Modern Genetics
Examined crosses involving seven different characters

3. Mendel’s Work

4. Mendel’s Laws Segregation
a) Members of a gene pair segregate into separate gametes
b) One-half of the gametes has one member, the other half, the other
Independent assortment--during gamete formation, segregation in a gene pair is independent of other gene pairs

5. Monohybrid Crosses
Cross between pure lines differing in a single character of interest
What Mendel Observed
The F1 were all Yellow
However, Green Segregated out in F2
Strong evidence for discrete units of heredity , as "green" unit obviously present in F1, appears in F2
3:1 ratio of Yellow : Green in F2

6. Mendel also found that Parental, F1, and F2 Yellow peas behaved quite differently
When examined each F2 yellow family separately, Mendel found
2/3 of the F2 yellows give 1/2 yellow, 1/2 green
1/3 of F2 yellows gave all yellow progeny

7. Mendel' s Explanation
Genetic information exists as discrete units occurring in pairs
YY is the genotype of the pure Yellow line
yy the genotype of pure Green line
Y dominant to y (y is recessive to Y)
YY, Yy (denoted by Y-) = Yellow
yy = green

8. heterozygous (hybrid)
Baby Steps
BABY STEPS: 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a p-square 4. "split" the letters of the genotype for each parent & put them "outside" the p-square 5. determine the possible genotypes of the offspring by filling in the p-square 6. summarize results (genotypes & phenotypes of offspring)
Symbol
Genotype Name
Phenotype RR
homozygous (pure) dominant
red thoat Rr
heterozygous (hybrid)
red throat rr
homozygous (pure) recessive
white throat
Parent Pea Plants  ("P" Generation)
Offspring  ("F1" Generation)
Genotypes: Tt x tt
Phenotypes: tall x short
Genotypes: 50% (2/4)  Tt 50% (2/4) tt
Phenotypes: 50% tall 50% short

9. Dominant and Recessive Genes - Examples
Complete Dominance – the dominant allele masks or covers the recessive allele
Homozygous Green pod x Yellow pod
Homozygous Green pod x Heterozygous Green pod
Heterozygous Purple Flowers x White Flowers
Heterozygous Tall Plant x Dwarf Plant
Homozygous Inflated pod x Wrinkled Pod
Cross between two pods from above (F2=F1xF1)

10. Test Cross
Preformed to determine whether a dominant phenotype is homozygous dominant (pure bred) or heterozygous (hybrid)
The cross is always done between a individual with a dominant phenotype and an individual that is homozygous recessive
Results if the individual in question is homozygous dominant
All offspring will be dominant phenotype
Results if the individual in question is heterozygous
Offspring will be half dominant and half recessive phenotype
A? x aa

11. Dihybrid Crosses Examples:
Crossing pure-breeding lines differing in two characters
Examples:
Wrinkled Homozygous Yellow Seed x Homozygous Round Green Seed
Heterozygous Tall Plant with Homozygous Axial Flowers x Dwarf Plant with terminal Flowers
Pure Breed Round Green Seed x Pure Breed Wrinkled Yellow Seed (F1 and F2) – Know this ratio

12. 9:3:3:1 Ratio
When crossing two opposing pure breed plants the F1 generation is always heterozygous and the F2 is always 9:3:3:1.

13. Levels of Dominance
When two alleles are equally dominant, they interact to produce new phenotypes
Incomplete Dominance – blending of the two traits
Co-Dominance– both traits will be shown in the offspring

14. Examples of Levels of Dominance
Example of Incomplete Dominance
Four-o’clock plants
P1 CRCR (red flowers) x CWCW (white flowers)
F1 CRCW (all pink flowers)
Example of Codominance
Cattle
P1 HRHR (red cow) x HWHW (white bull)
F1 HRHW (roan calves)

15. Multiple Alleles When more than two different alleles control a trait
The ABO blood group is a nice example, three alleles
IA, IB are codominant, IA and IB have dominance over i

16. Lethal Alleles
Manx gene in cats
Mm: tail-less
mm: normal
MM: dead

17. Multiple Gene Interaction
Black Labrador
B- E -
Brown (or Chocolate) Labrador
bb E -
Golden Labrador
-- ee
Individual here most likely is B- ee
as black pigment on lips and nose
Coat color in Labrador retrievers
BB, Bb = Black
bb = Brown (Chocolate)
Both color genes require E- genotype for pigment deposition.

18. Using Probability Rule of independent Events The Product Rule
Chance has no memory, each event or occurrence must be regarded as an individual event
The Product Rule
The probability of independent events occurring simultaneously is equal to the product of these event occurring independently