1. Non-Mendelian Genetics
Gene expression that varies from typical Mendelian ratios

2. Mendelian Genetics Review
Two possible alleles for a single gene
Dominant variation (B)
Recessive variation (b)
When the dominant allele is present in the genotype, it is always expressed in the phenotype
Recessive allele is only expressed when gene is homozygous recessive

3. Mendelian Genetics Review

4. Non-Mendelian Genetics
Some traits don’t follow the dominant/recessive rules outlined by Mendel’s Laws of Inheritance
Non-Mendelian Patterns of Inheritance:
Co-dominance
Incomplete dominance
Multiple alleles
Lethal genes
Polygenetic traits

5. Incomplete Dominance Genotype of individual is heterozygous
Alleles are not completely dominant over the other
Phenotype of heterozygote is a blending of the two homozygous phenotypes
Example: Snapdragons

6. Incomplete Dominance: Snapdragons
R = red R’ = white RR = red flower R’R’ = white flower RR’ = pink flower

7. Incomplete Dominance: Snapdragons
RR X R’R’
RR’ X RR’

8. Co-dominance Genotype of individual is heterozygous
Full expression of both alleles
Phenotype of heterozygote is neither dominant or recessive
Example: Roan Cattle, Speckled Chicken

9. Co-dominance: Roan Cattle
RR X WW

10. Co-dominance: Roan Cattle
RW X RW

11. Alternative Notation Homozygous Dominant (Red) RR
Homozygous Recessive (White) WW
Heterozygous (Roan) RW
Colour-determining Allele C
Homozygous Dominant (Red)
CRCR
Homozygous Recessive (White)
CWCW
Heterozygous (Roan)
CRCW

12. Multiple Alleles
Genes can have many possible alleles, but an individual can only carry 2 of those alleles max
One from each parent
Example: ABO Blood types with 3 alleles

13. Multiple Alleles: ABO Blood Types
What is blood made of?
Red blood cells
Contain hemoglobin, transport O2 and CO2 throughout the body
White blood cells
Fight infection
Platelets
Help blood to clot
Plasma
Fluid which contains salts and various kinds of proteins

14. Multiple Alleles: ABO Blood Types
Determining blood type
Protein molecules found on RBC and in blood plasma determine blood type on an individual
Antigens are located on the surface of blood cells
Antibodies are in the blood plasma

15. Multiple Alleles: ABO Blood Types
Different Blood Groups
Blood Group A
IA IA + IA i or AA + AO
Have A antigens on the surface of red blood cells and B antibodies in blood plasma
Blood Group B
IB IB + IB i or BB + BO
Have B antigens on the surface of red blood cells and A antibodies in blood plasma

16. Multiple Alleles: ABO Blood Types
Different Blood Groups
Blood Group AB
IA IB or AB
Have both A and B antigens on the surface of the red blood cells and no A or B antibodies
Blood Group O
i i or OO
Have neither A or B antigens on the surface of red blood cells, but have both A and B antibodies in blood plasma

17. Multiple Alleles: ABO Blood Types
Blood Transfusions
The transfusion will work if a person who is going to receive blood has a blood group that doesn’t have antibodies against the donor’s antigens
Blood Group
Genotype
Antigens
Antibodies
Can give blood to
Can receive blood from AB
A and B A B O
None

18. Lethal Alelles Some alleles are lethal when present as homozygous
Can apply to dominant or recessive allele/trait
Example: Coat colour in mice, Creeper gene in Chickens

19. Lethal Genes: Mice Coat Colour
Lethal genes were first observed in mice while studying coat colour gene
Expected phenotype ratio was 3:1 from a heterozygote cross
Observed phenotype ratio was 2:1

20. Lethal Gene: Mice Coat Colour
After several test crosses,
Yellow mice were found to be heterozygotes
White mice were homozygous recessive
No homozygous dominant yellow mice were obtained from crosses

21. Lethal Genes Creeper Gene
Lethal genes have also been observed in chickens,
When developing embryo contains two copies of a recessive allele, the embryo dies in the eggshell
Chick heterozygous with creeper allele will survive

22. Polygenic Traits
When more than two alleles and multiple genes control the expression of a trait
Examples: Height, skin colour, and hair colour in humans

23. Polygenetic Traits
Traits like height display a continuous distribution where phenotypes vary along a continuum

24. Polygenic Expression
Workers A, B, and C carry out steps for painting a design on a poster
Like genes a, b, and c are the instructions
Worker A puts paint in the tray; a tells it how
Worker B adds dye to the pain; b tells it what colour
Worker C paints a design on the poster; c tells it what design

25. Polygenic Expression
If looking at this as a genetic pathway, the workers and instructions would be invisible
The only part we would see is the output, the poster
The phenotype

26. Polygenetic Traits Epistasis
When the effect of one gene is dependent on the presence of one or more “modifier genes”
Often the proteins the genes code for work together in the same processes

27. Polygenic Expression: Epistasis
Adding epistasis:
A version (or allele) of a is broken so it contains no instructions
Worker A couldn’t put paint into the tray
Workers B + C still do their jobs
Output/Phenotpe: Blank Poster
The broken version of a is epistatic to b and c
The important aspect of epistasis is that it doesn’t just influence the phenotype, it hides the output of another gene or genes.

28. Polygenic Expression: Epistasis

29. Epistasis: Lab Colour Black Brown Yellow BBEE BBEe BbEE BbEe bbEE bbEe
Yellow (Dudley)
bbee

30. Epistasis: Lab Colour Yellow Yellow (Dudley) BBee Bbee bbee

31. Exploring Epistasis http://ansci.cornell.edu/usdagen/epistasis.html
Recessive masking epistasis
Dominant masking epistasis
Modifying epistasis
Definition/description
Example
2 Punnett Squares
Parental cross: AABB x aabb
F1 cross
Summarize phenotypes of offspring based on epistatic pattern