Transcript Beyond Mendel - Lake Station Community Schools

Beyond Mendel 11.3
Into 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 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

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
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
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
Blood
Antibodies Reactions When Blood from Groups Below Is
Group
Genotypes Red Blood Cells Present in Mixed with Antibodies from Groups at Left
(Phenotype)
Blood
A
B
AB
O
Carbohydrate A
IAIA
Anti-B
A
or
IAi
Carbohydrate B
IBIB
B
Anti-A
or
IBi
AB
IAIB
—
O
ii
Anti-A
Anti-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 gey
 These genes code for the formation of
the pigment melanin
 The 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 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

The 2 Gene Model
- B is dominant to all other allelesBBGG,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?