1. Patterns of Inheritance
The manner in which a gene is transmitted

2. 5 Patterns of Inheritance
Incomplete Dominance
Co dominance
Autosomal Dominant
Autosomal Recessive
X-linked
There are five basic modes of inheritance for single-gene diseases: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and mitochondrial.

3. Beyond Mendelian Genetics: Incomplete Dominance
Mendel was lucky!
Traits he chose in the
pea plant showed up
very clearly…
One allele was dominant over another, so phenotypes were easy to recognize.
But sometimes phenotypes are not very obvious…

4. Incomplete Dominance – Neither trait expressed
Snapdragon flowers come in many colors.
If you cross a red snapdragon (RR)
with a white snapdragon (rr)
You get PINK flowers (Rr)!
R R
r r 
Not all genetic disorders are inherited in a dominant–recessive pattern. In incomplete dominance, the offspring express a heterozygous phenotype that is intermediate between one parent’s homozygous dominant trait and the other parent’s homozygous recessive trait. An example of this can be seen in snapdragons when red-flowered plants and white-flowered plants are crossed to produce pink-flowered plants. I
Heterozygous genotype results in an Intermediate phenotype (blended trait)
R r

5. Incomplete dominance R r R r
When F1 generation (all pink flowers) is self
pollinated, the F2 generation is 1:2:1
red, pink, white
Incomplete Dominance
R r
R R
R r
r r R r

6. Incomplete dominance  A pink with a red? 
What happens if you cross a pink with a white? 
A pink with a red? 

7. Incomplete Dominance Both alleles contribute to phenotype
Mixing of parental traits
Eg a gene for hair texture: curly hair allele from one parent and straight-hair allele from other  wavy hair
In humans, incomplete dominance occurs with one of the genes for hair texture. When one parent passes a curly hair allele (the incompletely dominant allele) and the other parent passes a straight-hair allele, the effect on the offspring will be intermediate, resulting in hair that is wavy.

8. Codominance Both alleles expressed, NOT mixed Each trait is retained
equal, distinct, and simultaneous expression of both parents’ different alleles

9. Co-dominance Both traits expressed.
EG. An animal with allele for white hair and an allele for red hair produce a roan- coloured coat (both white  hairs and red hairs, not blended). 

10. Codominance

11. Codominance with Multiple Alleles: Blood Type
Multiple alleles control the ABO blood groups in humans.
The A and B alleles are codominant to each other, and the O allele is recessive
A Type x B Type = A and B type
A, B, O alleles A, B, AB, O blood
A classic example of codominance in humans is ABO blood type. People are blood type A if they have an allele for an enzyme that facilitates the production of surface antigen A on their erythrocytes. This allele is designated IA. In the same manner, people are blood type B if they express an enzyme for the production of surface antigen B. People who have alleles for both enzymes (IA and IB) produce both surface antigens A and B. As a result, they are blood type AB. Because the effect of both alleles (or enzymes) is observed, we say that the IA and IB alleles are codominant. There is also a third allele that determines blood type. This allele (i) produces a nonfunctional enzyme. People who have two i alleles do not produce either A or B surface antigens: they have type O blood. If a person has IA and i alleles, the person will have blood type A. Notice that it does not make any difference whether a person has two IAalleles or one IA and one i allele. In both cases, the person is blood type A. Because IA masks i, we say that IA is dominant to i. Table 4 summarizes the expression of blood type.

12. Blood Type

14. Polygenic Inheritance (multifactorial inheritance)
More than one gene involved in determining a particular characteristic, e.g. height or skin colour.
not to be confused with multiple alleles
Say that the genes A and B control human height. The dominant allele would be for tall and the recessive allele will be for short. However, the total height depends on the amount of tall genes you have:
AABB
aABB, AaBB, AAbB, AABb
AaBb, aABb, AAbb, AabB, aABb, aaBB
Aabb, aAbb, aaBb, aabB
aabb

15. Sex Linked Inheritance
Genes that are carried by either sex chromosome
male is hemizygous.

16. Sex Linked Inheritance: Color Blindness

17. Sex Linked Inheritance: Hemophilia
blood-clotting disorder caused by a mutation in a clotting factor
Queen Victoria of England was a carrier of the gene for hemophilia. 
Queen Victoria of England was a carrier of the gene for hemophilia. and many of her descendants carried what was once called "Royal disease"
She passed the harmful allele for this X-linked trait on to one of her four sons and at least two of her five daughters.  Her son Leopold had the disease and died at age 30, while her daughters were only carriers.  As a result of marrying into other European royal families, the princesses Alice and Beatrice spread hemophilia to Russia, Germany, and Spain.  By the early 20th century, ten of Victoria's descendants had hemophilia.  All of them were men, as expected.
How do we track these ?

18. Pedigree Analysis
Used to study trait inheritance in humans and predict how a disease is transmitted in families
the trait must cause a phenotype
females are circles
males are squares.
filled in symbol indicates that individual has the trait of interest.
partially filled = carriers (heterozygotes)
inheritance patterns describe how a disease is transmitted in families.
These patterns help to predict the recurrence risk for relatives.
In general, inheritance patterns for single gene disorders are classified based on whether they are autosomal or X-linked and whether they have a dominant or recessive pattern of inheritance. These disorders are called Mendelian disorders, after the geneticist Gregor Mendel.

20. Eg female in the third row (third generation) has the trait
Eg female in the third row (third generation) has the trait. However, neither of her parents had that trait. trait is most likely a recessive trait and an individual must have two copies of the allele in order for it to be expressed. For her to have this disorder, both of her parents must be carriers, heterozygous for the normal allele and the allele that causes the disorder.
The affected individual is homozygous recessive, pp, and both of her parents are Pp. The remaining individuals all have at least one P allele, but we do not know if they are homozygous or heterozygous.