Download Genetics After Mendel - Ms. Pasic

Genetics After Mendel
Genetics After Mendel
•Single factor inheritance
•Mendel found traits as
dominant or recessive
•Some instances where the
former rule does not
apply:
•Incomplete Dominance
•Co-dominance
•Multiple Alleles
Incomplete Dominance
A blending of the two traits occur,
giving an intermediate expression.
Incomplete
Dominance
Different alleles of
a gene are
expressed in the
heterozygous
condition to
produce an
intermediate
phenotype
Co-dominance
RR
WW
P
•Both alleles for a
trait are dominant
•Both alleles are
expressed in the
heterozygous
individual
F1
RW
•A red bull
crossed with a
white cow
produces a roan
calf
My
genotype is
RW and my
phenotype
is roan!
Co-dominance
RW
RW
F1
•Roan has
intermingled
white and red hair
F2
RR
RW
RW
WW
•1:2:1 phenotypic
ratio
Multiple Alleles
“A pattern of inheritance when a gene
may have more than two alleles for any
given trait.”
Ex. Human Blood Types
ABO BLOOD TYPES
The letters refer to two different kinds of
molecules (antigens), type “A” and type “B”
present on the surface of red blood cells (RBC).
The ABO blood type system uses the presence or
absence of these molecules to categorize blood
into the four types.
ABO BLOOD TYPES
There are 4 different phenotypic blood groups:
1. A  has antigen A on RBC (red blood cell)
2. B  has antigen B on RBC (red blood cell)
3. AB has BOTH A and B antigen on RBC
4. O has no antigen
Positive or Negative?
• Another level of specificity is added to blood type by
examining the presence or absence of the Rh factor (a
protein).
•Each blood type is either
• positive “+” (has the Rh protein)
• negative “-” (no Rh protein).
For example, a person whose blood type is“A positive” (A +),
has both type A and Rh proteins on the surface of their red
blood cells.
BLOOD TYPE IS GENETIC ......
• Blood type is an example of multiple alleles since it
involves 3 possible alleles for a gene.
•A
•B
•O
• The A and B antigen molecules on the surface of red
blood cells are produced by two different alleles of the
same gene: allele A and allele B.
• A third version of this gene, the O allele, codes for a
protein that is not functional and does not produce
surface molecules.
•Two copies of the gene are inherited, one from each
parent.
•A and B are CODOMINANT and O is recessive.
•Rh + is dominant to Rh -.
•The possible combinations of alleles produce blood
types in the following way:
Phenotype Genotype
A
AA or AO
B
BB or BO
AB
AB
O
OO
WHO’S YOUR DADDY??
PATERNITY CASE QUESTION
Minnie Mouse has type O blood while her husband Mickey mouse
has type A blood. Baby Mickey Jr. has type B blood. Mickey Mouse
suspects that frisky Donald Duck (type AB blood) may be the
biological father of Mickey Jr. Given this information (& ignoring
species differences), can you solve this paternity dilemma for
troubled Mickey? Show all possible punnett squares as evidence to
support your answer.
Another example....
Daddy is AB- and mommy is O+. What would all
the possible offspring’s blood type be?
WHEN BLOOD TYPES MIX
• Blood plasma is packed with proteins called antibodies.
The body produces a wide variety of antibodies that will
recognize and attack foreign molecules that may enter
from the outside world.
• When conducting a blood transfusion, it is important to
attain compatibility between the antigens present on the
RBC of the donor and the antibodies present in the
recipient’s plasma.
If the antibodies present in the recipient’s plasma
recognize the donor’s antigens as foreign, an immune
response will be triggered resulting in blood clotting or
agglutination.
AGGLUTINATION – Blood Transfusion
Blood Type
(phenotype)
Genotype
Antibodies in
recipient
Type A
AA or AO
Antibody B
Type B
BB or BO
Antibody A
Type AB
AB
None
Type O
OO
Antibody A and B
• People with type O blood
are universal donors because
there are no antigens on the
surface of the red blood cells
that can trigger an immune
response.
• People with type AB blood
are universal recipients
because they do not have any
antibodies that will recognize
type A or B antigens.
•A person with Rh+ blood does not have Rh
antibodies, therefore, you can always give Rh- blood
to an Rh+ recipient.
•A person with Rh- blood can develop Rh antibody if
given Rh+ blood, therefore, you cannot give Rh+
blood to an Rh- recipient.
•AB+ is the universal recipient because it can receive
all blood types due to the fact the recipient does not
have antibodies present.
•O- is the universal donor because it can be given to
all blood types due to the absences of antigens on the
surface of RBCs. O- can only receive O-.
Homework:
Page 196: 1-3 and 6-8