1. Into the Genetic Frontier
Beyond Mendel 11.3
Into the Genetic Frontier

2. Genes can be inherited based on various patterns
Mendel’s Dominance vs. Recessive
Incomplete dominance
Co-dominance
Multiple alleles
Polygenic genes

3. Incomplete Dominance
In this pattern neither allele is considered recessive
Heterozygous conditions produce a blend of the two traits creating a third phenotype.

4. Co-dominance
In this pattern much like incomplete dominance, neither allele is considered recessive
In a heterozygous condition where each type of allele is present the phenotype displays both traits from each allele
There are 3 possible phenotypes

5. Multiple alleles
In this pattern there is more than just two alleles (3 or more)
Combinations of other patterns
Ex. Some alleles behave in a dominant/recessive fashion while other alleles display a co-dominant or incomplete dominant relationship
This can lead to multiple phenotypes

6. There are 4 Human Blood Types
A, B, AB & O = 4 phenotypes
Blood type is controlled by one gene, with 3 different alleles – A, B and O
The 3 alleles can be combined to produce 6 different genotypes
AA BB
AO BO
AB OO

7. Inheritance of Blood Type
Is a mix of complete dominance and codominance
- AA & AO produce type A blood
- BB & BO produce type B blood
- AB produces type AB blood
- OO produces type O blood
From this we can infer that both A & B alleles are dominant to the O allele
The A allele is codominant with the B allele

8. Determining Possible Outcomes
Notating Blood Type
IA = A allele
IB = B allele
i = O allele
Example a person who
heterozygous for A blood = IA i
And a person with O blood = i i
How would a person who is homozygous for B blood be notated?
- IB IB
How would a person who is heterozygous for B blood be notated?
- IB i

9. What exactly is blood type?
Each blood type is the result of a specific combination of proteins found on the blood cells called antigens and proteins found in the blood plasma called antibodies
- type A blood = A antigens & B antibodies
- type B blood = B antigens & A antibodies
- type AB blood = both A & B antigens & no antibodies
- type O blood = no antigens & both A & B antibodies

10. Why is Blood Typing Important?
If a person is given blood with antigens that their blood plasma contains antibodies for, the antibodies will attach to the blood causing it to clump
- this clumping is called agglutination

11. Figure 9.20 Blood Group (Phenotype) Antibodies Present in Blood
Reactions When Blood from Groups Below Is
Mixed with Antibodies from Groups at Left
Genotypes
Red Blood Cells O A B AB
Carbohydrate A
IAIA or
IAi A
Anti-B
Carbohydrate B
IBIB or
IBi B
Anti-A AB
IAIB —
Figure 9.20 Multiple alleles for the ABO blood groups.
Anti-A
Anti-B O ii
Figure 9.20

12. Polygenic traits Some traits which have many possible
phenotypes are controlled by more than one gene.
- the interactions of these genes allows for the large numbers of phenotypes.
- human examples: Hair, eye and skin color

13. The Inheritance of Eye Color
Only partially understood.
at least 3 different genes with 2 alleles each are responsible for eye color.
– bey 1 bey 2 and gey
These genes code for the formation of the pigment melanin
The function of only 2 of the 3 genes is currently understood

14. The Inheritance of Eye Color as it is Currently Understood
Known as the 2 gene model
One gene known as bey 2 has 2 alleles B for brown eyes and b for blue eyes
The other gene known as gey has 2 alleles G codes for green eyes and g for blue eyes
Evolution of eye color- not understood. One theory melanin was useful in tropical climates, but as people moved north, less sun required less melanin. One other idea, the color blue allows more light to pass through the iris reducing depression in the winter due to SADS

15. The 2 Gene Model - B is dominant to all other alleles-
BBGG,BBGg,BBgg,BbGG
BbGg,Bbgg = Brown eyes
- G is dominant to b
bbGG , bbGg = Green eyes
- bbgg only = blue eyes
How to figure out eye genetics – dihybrid cross

16. Genes and the Environment
The characteristics of any organism are not determined solely by the genes that organism inherits.
Genes provide a plan for development, but how that plan unfolds also depends on the environment.
The phenotype of an organism is only partly determined by its genotype.

17. Environment Can Influence Gene Expression
example: Siamese cats
- Siamese coloring is a partial
albinism. Most of the cat is white
-Black fur is only expressed in areas
where the temperature is lower than
the rest of the body
- if black hair is shaved and the area kept warm then the hair that grows back will be white
- if white hair is shaved and the area is cooled,
then the hair will grow back black
The Siamese color is recessive and only shows up in homo recessive cats. The same gene for fur color also controls crossed eyes associated with siamese. Albinism is associated with crossed eyes in many species Pleiotropy

18. In a certain fish, blue scales and red scales are codominant
In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales.

19. In snapdragons, flower color is controlled by incomplete dominance
In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. What happens when you breed 2 pink dragons?