1. 11-3 Heredity Following Different Rules
Mulitple Alleles, Sex-linked traits, and Polygenic Inheritance

2. Multiple Alleles Presence of more than 1 allele for a genetic trait
Mice fur
Pigeon feathers

3. Multiple Alleles in Humans
Blood Types
4 types
A, B, and O Rh
Different blood types determined by the presence of a protein on blood’s surface

4. Blood Groups
Human blood comes in a variety of genetically determined blood groups
Using the wrong blood during a blood transfusion can be fatal
A number of genes help determine blood type but we will focus on two:
ABO blood groups
Rh blood groups

5. Blood Groups—the easy one first
The Rh blood group is determined by a single gene with 2 alleles—positive and negative
The positive allele is dominant
You need two Rh- alleles (Rh-/Rh-) to be Rh negative

6. ABO Blood Groups This is a case of multiple alleles
There are 3 alleles for this gene—A, B, and O.
AND…A and B are codominant!
O is recessive to A and B
Alleles A and B produce antigens (which are carbohydrates) on the surface of red blood cells
O produces NO antigens

7. ABO Blood Groups—the wrong blood can be FATAL
Antigens are recognized by the immune system and induce an immune response
If the wrong blood is transfused, the body will respond to these antigens by producing antibodies
Antibodies are named for what they attack
Antibodies bind to the foreign molecule (the antigen) and blood clumping will occur, which leads to blood clotting, which leads to death

8. ABO Blood Groups If you have blood type A, then you have:
The “A” antigen on the surface or your RBCs
You have anti-B antibodies
You can receive type A blood and type O blood
Remember: Your antibodies are named for what they attack—so if you received type AB or type B blood then clumping would occur.

11. ABO Blood Groups Try this cross
Cross a person who’s genotype is IAIA with a person who is IAIB.
Give the possible genotypes and phenotypes

12. Cross a person who’s genotype is IAIA with a person who is IAIB
Gametes= IA ,IA and IA, IB
Cross: IA IA IA
IAIA
IAIA
IAIB IB
IAIB

13. Genotypes= ½ IAIA, ½ IAIB
Phenotypes = ½Type A, ½ Type AB

14. Sex Linked Genes Many sex-linked genes are found on the X-chromosome
What are linked genes?
They can be separated during meiosis through CROSSING OVER
Genes carried on the X or Y chromosome are sex linked because they are on the sex chromosomes
Many sex-linked genes are found on the X-chromosome

15. Sex Linked Genes
The X chromosome has many genes that are important for growth and development
The Y-chromosome only contains a few genes
All X-linked traits are expressed in males
WHY???????
Males only have 1 copy of the X chromosome, while females need 2 copies of the defective gene

16. Carrier:
An individual possessing an unexpressed recessive trait

17. Sex-Linked Gene Disorders
Colorblindness
3 human genes associated with color vision are located on the X-chromosome
In males, a defective version of any one of these produces colorblindness
Females must receive 2 copies of the allele to be colorblind
XCXc
XCXC
XCY
XcY

18. Sex-Linked Gene Disorders cont.
Hemophilia
2 important genes on the X-chromosome that code for proteins control blood clotting
A recessive allele in either of these 2 genes may lead to hemophilia
“bleeders disease”
Injections of normal clotting proteins prevent death

19. Sex-Influenced Genes A person’s phenotype is affected by their sex
Ex: Pattern Baldness
WOMEN: MEN:
BB: not bald BB: not bald
Bb: not bald Bb: bald
 bb: bald bb: bald

21. X-Chromosome Inactivation
Females have 2 X-chromosomes… if 1 is enough for males, how does the cell “adjust” to the extra x-chromosome in females?
One X-chromosome is randomly switched off
Condenses and is called a Barr body

23. Polygenic Inheritance
Remember, poly = many, genic = genes
So…polygenic inheritance means
A trait that is controlled by 2 or more genes
Examples:
Skin color
Cob length

24. Upper case and lower case represent alleles BUT
Upper case does not mean that it is dominant
All heterozygous alleles have intermediate phenotypes
Examples:
aabbcc: very little melanin in skin
AABBCC: a lot of melanin in skin

26. Other Influences on Gene Expression
External Environment
Temperature
Nutrition
Light
Chemicals
Infectious agent

27. Phenotype is influenced by your environment (ex: nutrition & exercise)
Average height is 10cm more than it was in the 1800’s in the US & Europe due to nutritional improvements
Genes that are denied a proper environment in which to reach full expression in 1 generation, can achieve full potential in a later generation (genes are inherited, the environment is not)

28. Internal Environment
Males and females have different structures and hormones therefore genes are expressed differently
Peacock feathers
Human bald patterns
Age