9.5.2 Codominance and Multiple Alleles: ABO Blood Genes

Question 1

note

Answer 1

• • In humans, the four blood types are A, B, AB, and O. Type AB displays codominance.
  • Many genes of populations have more than two possible alleles, a phenomenon called multiple alleles. An example is blood groups in humans.
  • The presence or absence of antibodies in the blood governs transfusions between the various blood groups.
• Blood groups are classified by the type of glycolipid
  embedded in the cell membrane. An individual with type A blood has A antigens on the surface of the cell. Type B blood has B antigens on the surface of the cell. Type AB blood has both A and B antigens on the cell surface and is an example of codominance. Type O blood has neither A nor B antigens.
• The glycolipids are called antigens because they have an antigenic effect with certain other blood types.
• People with type A blood have antibodies to the B antigen. The antibodies are produced in response to bacteria that have antigens similar to the blood group antigens. Similarly, people with type B blood have antibodies to the type A antigen. AB blood types don’t produce antibodies to either A or B antigens. Type O blood has both A and B antigens.
• The production of antibodies has an impact on blood
  transfusions. A type A person can only receive blood from another type A or an O individual. A type B person can only receive blood from another type B or an O individual. Type AB people can receive blood from any of the blood groups. Type O can only receive blood from another O individual. Type O is considered the universal donor because they can donate to any of the other groups.

Question 2

What is a possible genotype of a person with anti-A and anti-B antibodies?

Answer 2

• ii

Question 3

A man who has a genotype of I Ai marries a woman of the genotype I Ai. What is the probability the first child will be a boy with type O blood?

Answer 3

• 1/8

Question 4

Why is a person with blood type AB considered the “universal recipient”?

Answer 4

• A person with type AB blood does not produce any antibodies.

Question 5

When members of the fictitious species Arnoldi schwarzenhegaroff are crossed, the following results are obtained:
A. burlybody × brucewillis produced 52 burlybody, and 48 brucewillis;
B. burlybody × twiggy produced 99 brucewillis;
C. brucewillis × brucewillis produced 24 burlybody, 53 brucewillis, and 27 twiggy
Which hypothesis would be consistent with the results?

Answer 5

• The brucewillis body shape is the result of heterozygous codominant alleles.

Question 6

Which of the following explains codominance?

Answer 6

• Both alleles are distinctly expressed in a heterozygote

Question 7

A woman who has type A blood marries a man with type B blood. Their first child has type O blood. What are the expected genotypic frequencies of all possible offspring that the parents can have?

Answer 7

• 1/4 I AI B, 1/4 I Ai, 1/4 I Bi, 1/4 ii

Question 8

Which two human blood-group phenotypes can be the result of more than one genotype?

Answer 8

• Type A and Type B

Question 9

Which two alleles for blood type are codominant?

Answer 9

• I A and I B

Question 10

What will occur if someone with the genotype I AI B donated blood to someone with the genotype ii?

Answer 10

• The anti-A and anti-B antibodies in the recipient’s blood will attack the transfused blood

Question 11

A woman with type B blood

Answer 11

• can receive blood from a type O donor

Question 12

How many alleles are responsible for producing the four possible blood type phenotypes in humans?

Answer 12

• 3

Question 13

What are two possible genotypes of a person who has anti-B antibodies?

Answer 13

• I Ai, ii