1. Exceptions to the Rule Not all of Mendel’s rules apply to all genes.
Sometimes more than one allele is dominant
Sometimes neither allele is dominant or recessive
Other times genes are carried
on multiple alleles (more than 2 options!)

2. Codominance Two alleles are both expressed as a dominant phenotype
Both are seen at the SAME time!
Coat color in cows
RR: Red
WW: White
RW: Roan, white with
red spots

3. Codominance Example RW WW RW WW R W W
Coat color in cows displays codominance. Use the Punnett Square to determine the possible phenotypes of offspring of a white cow with a roan cow.
R W W RW WW RW WW

4. + Allele for Black cat (B)
Codominance
More examples of Codominance
= Tabby cat
(BT)
Allele for Tan cat (T)
+ Allele for Black cat (B)

5. Codominance = Black & White Chicken More examples of Codominance
(BW)
Allele for White chicken (W)
+ Allele for Black chicken (B)

6. Incomplete Dominance
Sometimes one allele is not completely dominant over another.
Called incomplete dominance
The heterozygous phenotype is a blending of the two homozygous phenotypes.

7. Incomplete Dominance Examples: Four o’clock flowers rr=red ww=white
rw=pink (blending of the
two alleles)

8. Incomplete Dominance Example
Flower color in four o’clock flowers displays incomplete dominance. Use the Punnett Square to determine the possible phenotypes of offspring of a pink flower with a red flower.
r w r rr rw rr rw

9. Incomplete Dominance Examples: Rabbits ll= long fur (angora rabbits)
ss= short fur (rex rabbits)
ls=medium length fur
(blending of the two alleles)

10. Multiple Alleles
More than two allele choices are present for each trait.
Example: Coat Color in Rabbits (4 possible alleles!)
Cch = chinchilla
C = full color
c = no color
Ch= Himalayan color

11. Multiple Alleles Coat Color in Rabbits
C=full color
Cch= chinchilla
Ch= Himalayan color
c = no color
There is a hierarchy of dominance for this trait.
For example, a rabbit with genotype CCch will have a full coat color. A rabbit with genotype Cch Ch will be chinchilla.

12. Multiple Alleles ABO blood type has three alleles ABO Blood types:
A & B are codominant.
If both A and B are present, type is AB
Neither is recessive
O is recessive to both A and B
Individuals can be type A, B, AB, or O
Alleles are written IA, IB, or i.
If you are heterozygous for type A, your
genotype is IA i

13. Multiple Alleles ABO blood type has three alleles ABO Blood types:
If both A and B are present, type is AB (codominance)
Neither is recessive
Individuals can be type A, B, AB, or O (recessive)
Alleles are written IA, IB, or i.
If you are type A (heterozygous) your
genotype is IA i

14. Type A Type B Type AB Type O IA IA IA i IBIB IB i IAIB ii
Blood Type (Phenotype)
Possible Genotypes
Type A
IA IA
IA i
Type B
IBIB
IB i
Type AB
IAIB
Type O ii

15. What is blood made up of? The red blood cells The white blood cells
contain hemoglobin.
Red blood cells transport O2 and CO2 to and from body tissues.
The white blood cells
fight infection.
The platelets
help the blood to clot
The plasma
Fluid which contains salts and various
kinds of proteins.

16. Determining Blood Type
Protein molecules found on the surface of RBC’s and in the blood plasma determine the blood type of an individual.
Antigens are located on the surface of the red blood cells
Antibodies are in the blood plasma.

17. What are the different blood groups?
Blood group A (IA IA ), (IA i) have A antigens on the surface of red blood cells and B antibodies in blood plasma.
Blood group B (IBIB ), (IB i)
have B antigens on the surface of red blood cells and A antibodies in blood plasma.

18. What are the different blood groups?
Blood group AB (IA IB )
Have both A and B antigens on the surface of red blood cells and no A or B antibodies in blood plasma.
Blood group O (i i)
Have neither A or B antigens on the surface of red blood cells but have both A and B antibodies in blood plasma.

20. Blood transfusions – who can receive blood from whom?
The transfusion will work if a person who is going to receive blood has a blood group that doesn't have any antibodies against the donor blood's antigens.

21. People with blood group 0 are called "universal donors"
People with blood group AB are called "universal receivers."

22. Rh Factor Refers to another antigen on red blood cells
Dominant trait (D) is to have the antigen
Rh+
Recessive trait (d) is not to have it
Rh-
A person with Rh- blood will produce antibodies to Rh+ blood
Can be a problem in pregnancy – if mother is Rh-, and fetus is Rh+, her blood may begin to break down the blood of her baby!

23. Rh Factor Refers to another antigen on red blood cells
Dominant trait (D) is to have the antigen
Rh+
Recessive trait (d) is not to have it
Rh-

25. Sex-Linked Inheritance

26. Males have an X and a Y chromosome
Females have two X chromosomes
These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked genes.

27. The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome.
Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need.

28. Hemophilia Recessive trait
Disorder where individuals are missing the normal blood clotting protein.
Uncontrolled bleeds from minor cuts or bruises.
Female with hemophilia genotype: Xh Xh
Male with hemophilia genotype: XhY

29. Colorblindness Recessive Inability to see certain colors
Female with colorblindness genotype: Xc Xc
Male with colorblindness genotype: XcY

30. Colorblindness

31. Do any of these pictures look the same?!

32. Test time!

33. Duchenne Muscular Dystrophy
Recessive
Progressive weakening and loss of skeletal muscle.
Defective version of gene that codes for muscle protein
Female with DMD genotype: Xd Xd
Male with DMD genotype: XdY

34. EXAMPLE!!
A woman who is heterozygous for normal vision marries a man who is colorblind. What are the chances of them having a son or daughter who is colorblind?
**NOTE: You have to use X’s and Y’s, and read the punnett square separately for boys and girls!**

35. Xc Y XC XC Xc XC Y XcY Xc Xc Xc Woman: XC Xc Man: XcY
50% of females will have normal vision, but will be carriers
50% of females will be colorblind
50% of males will have normal vision
50% of males will be colorblind

36. Y Xh XH XH Xh XHY XH XHY XH Xh
A woman who is homozygous for normal blood clotting marries a man who has hemophilia. What are the chances of them having a son or daughter with hemophilia?
Woman: XH XH Man: Xh Y Y Xh XH
XH Xh
100% of daughters will have normal blood clotting, but will be carriers
100% of sons will have normal blood clotting
XHY XH
XHY
XH Xh

37. JK! Polygenic Traits Sometimes, multiple genes can control traits
Normally shows a wide array of phenotypes
Example: skin color
More than four genes control it…each with at least 2 different alleles
Lets try a cross!
JK!

38. Examples of polygenic traits in humans

39. Example of polygenic traits in humans

40. Genes and the Environment
The characteristics of an organism are not determined solely by the genes that organism inherits.
Genes provide the plan for development…but the environment can change how that plan unfolds!

41. Genes and the Environment
Example:
Western White Butterfly
If hatching in the Spring, wings would be darker than those hatching in the summer.
Reasoning…
The body temperature of the butterfly has to remain around degrees C to fly.
It is colder in spring, so they need darker pigment to absorb more heat!