Beyond Mendel 11.3Into the Genetic Frontier

Genes can be inherited based on various patterns

• Mendel’s Dominance vs. Recessive

• Incomplete dominance

• Co-dominance

• Multiple alleles

• Polygenic genes

Incomplete Dominance• In this pattern neither allele is considered recessive

• Heterozygous conditions produce a blend of the two traits creating a third phenotype.

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

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

There are 4 Human Blood Types

A, B, AB & O = 4 phenotypesBlood 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 BBAO BOAB OO

Inheritance of Blood TypeIs 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

Determining Possible Outcomes

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

Notating Blood Type IA = A allele IB = B allele i = O allele

Example a person who heterozygous for A blood = IA iAnd a person with O blood = i i

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

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

BloodGroup(Phenotype) O

GenotypesAntibodiesPresent inBlood

Red Blood CellsReactions When Blood from Groups Below IsMixed with Antibodies from Groups at Left

A B AB

O

A

B

AB

ii

IAIB

IBIB

orIBi

IAIA

or IAi

Carbohydrate A

Carbohydrate B

Anti-A

Anti-B

Anti-AAnti-B

—

Figure 9.20

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

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 geyThese genes code for the

formation of the pigment melaninThe function of only 2 of the 3

genes is currently understood

The Inheritance of Eye Color as it is Currently Understood

Known as the 2 gene modelOne gene known as bey 2 has 2 alleles B

for brown eyes and b for blue eyesThe other gene known as gey has 2

alleles G codes for green eyes and g for blue eyes

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

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.

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

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.

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?