Codominance In Humans
I. Codominance in Humans
A. Codominance is the phenotypes of both homozygotes are produced in the heterozygote.
1. Ex: sickle-cell disease
II. Sickle-cell disease
A. Homozygous for sickle-cell allele.
B. Oxygen-carrying protein hemoglobin differs by one amino acid from normal hemoglobin.
C. Defective hemoglobin forms crystal-like structures that change the shape of the red blood cells.
D. Normal red bloods cells are disc-shaped, but abnormal red blood cells are sickle-shaped or half- moon.
E. The change in shape occurs in the body’s narrow capillaries after hemoglobin delivers oxygen to the cells.
F. Heterozygous for the allele produce both normal & sickled hemoglobin (ex of codominance).
G. Have sickle-cell trait because they can show some signs of sickle-cell-related disorders if the availability of oxygen is reduced.
III. Multiple Alleles Govern Blood Type
A. Mendel’s laws of heredity also can be applied to traits that have more than two alleles.
B. The ABO blood group is a classic example of a single gene that has multiple alleles in humans.
C. Human Blood Types
Genotypes
Surface Molecules
Phenotypes
lA lA or lAli
A
A lB lB or lBi
B
B lA lB
A and B
AB
ii
NONE
O
IV. The importance of blood typing
A. 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
B. The ABO Blood Group
1. The gene for blood type, gene I, codes for a molecule that attaches to a membrane protein on the surface of red blood cells! The IA or IB 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
2. Phenotype A
3. The IA allele is dominant to i, so inheriting either the IAi alleles or the IAIA alleles from both parents will give you type A blood! Surface molecule A is produced.
4. Phenotype B
5. The IB
A. Codominance is the phenotypes of both homozygotes are produced in the heterozygote.
1. Ex: sickle-cell disease
II. Sickle-cell disease
A. Homozygous for sickle-cell allele.
B. Oxygen-carrying protein hemoglobin differs by one amino acid from normal hemoglobin.
C. Defective hemoglobin forms crystal-like structures that change the shape of the red blood cells.
D. Normal red bloods cells are disc-shaped, but abnormal red blood cells are sickle-shaped or half- moon.
E. The change in shape occurs in the body’s narrow capillaries after hemoglobin delivers oxygen to the cells.
F. Heterozygous for the allele produce both normal & sickled hemoglobin (ex of codominance).
G. Have sickle-cell trait because they can show some signs of sickle-cell-related disorders if the availability of oxygen is reduced.
III. Multiple Alleles Govern Blood Type
A. Mendel’s laws of heredity also can be applied to traits that have more than two alleles.
B. The ABO blood group is a classic example of a single gene that has multiple alleles in humans.
C. Human Blood Types
Genotypes
Surface Molecules
Phenotypes
lA lA or lAli
A
A lB lB or lBi
B
B lA lB
A and B
AB
ii
NONE
O
IV. The importance of blood typing
A. 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
B. The ABO Blood Group
1. The gene for blood type, gene I, codes for a molecule that attaches to a membrane protein on the surface of red blood cells! The IA or IB 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
2. Phenotype A
3. The IA allele is dominant to i, so inheriting either the IAi alleles or the IAIA alleles from both parents will give you type A blood! Surface molecule A is produced.
4. Phenotype B
5. The IB