Download Red-green color blindness

Shut up,
Darwin
So much
for
genius!
All of the inheritance patterns we have learned
about so far, such as the one’s from Mendel’s
experiments, are often referred to as simple
Mendelian inheritance.
This would include any
inheritance which is
controlled by a single
pair of alleles, one
dominant, and one
recessive.
Polygenic Inheritance
Many inheritance patterns are far more complex
than those studied by Mendel.
Some of these types of inheritance don’t even
involve chromosomes!
When inheritance follows the rule of dominance,
then the homozygous dominant, and the
heterozygous individuals all have the same
phenotype.
The allele for tall = T;
TT= tall
the allele for short = t
When traits are inherited in a pattern
Tt = tall
tt = short where the heterozygous individual is
intermediate between those of the
two homozygotes, then the pattern is
TT = tall called Incomplete Dominance.
tt = short
Tt = Average height
X
=
Red Snapdragons
White Snapdragons
Pink Snapdragons
When showing incomplete dominance, the alleles
look like this: R1=white R=red
Neither is dominant to the other, so no lower case
letter appears.
Can you predict what happens when you cross two
pink snapdragons? Do a punnett square crossing RR1 x RR1
R
R
R1
R1
RR
RR1
RR1
R1R1
The snapdragons appear
in the F2 generation in a
1:2:1 phenotypic ratio
The genotypic ratio is
also 1:2:1
This result supports Mendel’s law of
segregation, meaning that the alleles
combine during fertilization completely
randomly in four possible ways.
Codominance is apparent in a breed of chicken,
where black feathers are B, and white feathers are
W. Both are dominant, so both are expressed with
a capital letter.
When codominant alleles are expressed, both
phenotypes are present equally.
BW
BB
WW
X
=
Humans can have one of four possible blood types:
A; B; O; and AB
Human blood is separated into different classifications
because of the varying proteins contained in each blood
type's red blood cells.
These proteins are there to identify whether or not the blood in the
individual's body is it's own and not something the immune system
should destroy.
IAIA=Type A
IBIB=Type B
ii=Type O
IAIB=Type AB
The proteins in our blood cell’s
structure is controlled by three
alleles; i, IA and IB.
The i allele is the only recessive
allele IA and IB are both codominant
If the recessive allele i is paired with IB or IA, it's phenotypic expression
is hidden. When the IB and IA are together in a pair, both proteins A
and B are present and expressed.
Question:
What are the genotypes of a man and woman, each with
type A, and B blood respectively, who produce offspring
with types A, B, O and AB?
A
Let’s not forget to show
the offspring’s actual
genotypes!
Now it becomes obvious
what their genotypes
were.
I
AIB
IB IAB
i
A
IAi
i
IBBi
Oii
RH, or Rhesus factor is inherited separately from the blood
type, and follows the rules of polygenic inheritance. About
85% of humans globally contain the Rhesus positive
phenotype, which means they contain the Rh+ antigen on
the surface of their red blood cells.
A woman with Type O blood and a man who is Type
AB are expecting a child. What are the possible
blood types of the offspring?
This couple can only have
offspring that are types
A, and B.
i
IA
Can a person with type
AB blood ever
B
I
produce a child with
type O blood?
NO!!!
i
IAi
IAi
IBi
IBi
Blood groupings of humans not only follow the rules of
codominance, but also are determined through multiple
alleles. IA; IB; i
While many traits are controlled by a single pair of
alleles, some traits can be controlled by more than
two alleles. These traits are said to be carried and
expressed by multiple alleles.
In the case of rabbit fur color, there are four different
alleles which determine different phenotypes.
rabbit
Dark-gray colored Chinchilla
ch
c = dominant to
C=dominant to
Himalayan and to
all other alleles
white
Himalayan rabbit
ch = dominant
to white
White rabbit
c=
completely
recessive
Try predicting how many possible genotypes would code for
chinchilla rabbits.
Remember, while there may be multiple alleles in a population that determine a
trait, each individual only inherits a pair of these alleles…one from mother, and
one from father! Human blood types are not only codominant, but multiple allele!
Traits controlled by genes located on the sex
chromosomes are called sex-linked traits.
In humans, there are 23 pairs of chromosomes in all
autosomal cells within the body. The 23rd pair are sex
chromosomes.
The male genotype is XY, the female genotype is XX
The presence of
the Y
chromosome in
one of these
karyotypes,
makes one of
these individuals
a male. When
there are two
X’s, then it is a
female
The alleles for sex-linked traits are written as
superscripts of the X or Y chromosome…depending
upon which chromosome they are associated with.
Because males only inherit one X chromosome,
when a recessive trait is inherited on the X
chromosome there is no corresponding trait to
mask that trait on the Y chromosome…so the
recessive trait is always expressed
In fruit flies, the allele for eye color is on the X
of a whitechromosome. What would the genotype
eyed female look like? XrXr
XR=red eyes What would the genotype of a redRXr
X
eyed
heterozygous
female
look
like?
r
X =white eyes
What would the genotype of a red-eyed
homozygous dominant female look like?
XRXR
Predict what the genotype of a white-eyed male
would look like. XrY
Create a punnett square showing the mating results of a
homozygous dominant female fruit fly for eye-color, and a
male fruit fly with the recessive trait.
Because there is no second X chromosome in the male, it
cannot be homozygous. Instead, it is called hemizygous.
XR
XR
Xr
Y
XRXr
XRY
XRXr
XRY
What color eyes will the males
have?
What color eyes will the
females have?
Predict what genotypic
combinations would create
white-eyed male flies.
Thomas Hunt Morgan discovered that
traits were linked to sex chromosomes,
through his study of fruit flies.
Hemophilia is characterized by inability to form blood clots
because of deficiency in a clotting factor in the blood. The
frequency of hemophiliacs is about 1 in 10,000 males.
Affected individuals suffer from severe bleeding following
a relatively small injury like a cut or a bruise.
Duchenne Muscular Dystrophy affects young boys.
It is characterized by muscular degeneration and
weakness beginning at the age of 3 to 5 years and
progressing rapidly so that affected individuals are
wheel-chair bound by the time they are in their
teens and die in their early twenties because of
severe involvement of their respiratory muscles.
Red-green color blindness is
the inability to distinguish red
from green.
An individual with normal color vision will see a 5 revealed
in the dot pattern.
An individual with Red/Green (the most common) color
blindness will see a 2 revealed in the dots.
How can you
tell quickly,
that this must
be a sex-linked
trait?
Only the males have it!
Some traits, such as skin, eye color and height in
humans vary over a wide range.
These traits are governed by many genes, or
polygenic inheritance.
Skin Color: A Polygenic Trait
Scientists have found that when light-skinned
people mate with dark-skinned people, their
offspring have intermediate skin colors, similar to
what you might expect with incomplete dominance.
When intermediate skin-colored children mate with each
other, the resulting skin color range from the light-skin
color to the dark-skin color of the original parents.
X
=
Gametes contributed
by parents
ABC
ABc
AbC
Abc
aBC
aBc
abC
abc
ABC
6
5
5
4
5
4
4
3
ABc
5
4
4
3
4
3
3
2
AbC
5
4
4
3
4
3
3
2
Abc
4
3
3
2
3
2
2
1
aBC
5
4
4
3
4
3
3
2
aBc
4
3
3
2
3
2
2
1
abC
4
3
3
2
3
2
2
1
abc
3
2
2
1c
2
1
1
0
ABC = dark pigmentation
abc = light pigmentation
As you can see, this individual
offspring would inherit the darkest
pigmentation, whereas this offspring
would inherit the lightest
pigmentation.
This makes it easier to understand how two offspring of biracial
ancestry can actually pass on the darkest, or the lightest pigmentation
to their offspring (even though the odds are against it! )
AaBbCc x AaBbCc
What are the odds of this couple producing an
aabbcc individual? 1/64
AABBCC? 1/64
Sometimes the genetic makeup of an organism
determines only that organism’s potential to
develop and function in a particular way.
As the organism develops, many factors can
influence how the gene is expressed, or even
whether the gene is expressed at all.
Influence of external environment: Temperature,
nutrition, light,
chemicals, and
Influence of internal environment: infectious
diseases can
Hormones can
influence gene
influence horn
expression.
size in
mountain
sheep.
Arctic Fox