Download Ch. 12 Complex Inheritance

When the hybrid offspring shows an
intermediate phenotype between the two
parents.
Example: Flower color
CRCR = red
CWCW= white
CRCW = pink
High CholesterolLL= normal Cholesterol
LL’= High Cholesterol
L’L’ = Very High Cholesterol
https://www.youtube.com/watch?v=fHpMT7xJ
R3s
See Cholesterol Worksheet for info and Punnett Squares.
When the hybrid offspring shows both parental
traits.
Example: Roan Coat Color in horses
RR = red
R’R’ = white
RR’ = roan (has both red and white hairs).
Sickle Cell Anemia (codominance in humans)
• An inherited disease where people who have the
allele for sickle cell have defective hemoglobin,
causing misshaped blood cells that do not carry
enough oxygen .
• In the heterozygous form, the disease causes
anemia and pain, but also provides a tolerance to
malaria.
• https://www.youtube.com/watch?v=R4c3hUhhyc
• In the homozygous form, the disease can cause
organ failure and death.
Sickle-cell anemia
• The change in shape occurs in the body’s narrow
capillaries after the hemoglobin delivers oxygen to
the cells.
Normal red
blood cell
Sickle cell
Sickle-cell anemia
• Abnormally shaped blood cells, slow blood flow,
block small vessels, and result in tissue damage and
pain.
Normal red
blood cell
Sickle cell
AA= normal
AS= mild anemia- some sickle cells, some
normal- resist malaria infection
SS= disease, anemia, organ damage
https://www.youtube.com/watch?v=Zsbhvl2nVNE
What is the probability that a baby will have full
blown sickle cell disease if both parents have
mild sickle cell anemia?
NN = normal
NS = mild anemia
SS = full anemia
A
S
A
AA
AS
S
AS
SS
25% chance of SS
Multiple Alleles Govern Blood Type
• Mendel’s laws of heredity also can be applied to
traits that have more than two alleles.
• The ABO blood group is a classic example of a
single gene that has multiple alleles in humans.
Multiple Alleles Govern Blood Type
Human Blood Types
Genotypes Surface Molecules
A
lA lA or lAli
B
lB lB or lBi
lA lB
A and B
None
ii
Phenotypes
A
B
AB
O
The ABO Blood Group
• The gene for blood type, gene l, codes for a
molecule that attaches to a membrane protein
found on the surface of red blood cells.
• The lA and lB alleles each code for a different
molecule.
• Your immune system recognizes the red blood cells
as belonging to you. If cells with a different surface
molecule enter your body, your immune system will
attack them.
Phenotype A: Blood type A
• The lA allele is dominant
to i, so inheriting either
the lAi alleles or the lA lA
alleles from both
parents will give you
type A blood.
• Surface molecule A is
produced.
Surface molecule A
Phenotype B: Blood type B
• The lB allele is also
dominant to i.
• To have type B blood, you
must inherit the lB allele
from one parent and
either another lB allele or
the i allele from the other.
• Surface molecule B is produced.
Surface molecule B
Phenotype AB: Blood type AB
• The lA and lB alleles are
codominant.
Surface molecule B
• This means that if you
inherit the lA allele from one
parent and the lB allele from
the other, your red blood
cells will produce both
surface molecules and you
will have type AB blood.
Surface molecule A
Phenotype O: Blood type O
• The i allele is recessive
and produces no surface
molecules.
• Therefore, if you are
homozygous ii, your
blood cells have no
surface molecules and
you have blood type O.
The importance of blood typing
• Determining blood type is necessary before a
person can receive a blood transfusion because the
red blood cells of incompatible blood types could
clump together, causing death.
Blood type A
Blood cells have
surface protein
A
Blood type B
Blood cells have
surface protein
B
Blood type AB
Blood cells have
surface proteins
A and B
Blood type O
Blood cells have
no surface
proteins