BIOL 2500 - Topic 5 (part 2)

Codominance

Unlike in incomplete dominance where the 2 extremes are blended, in codominance, both the extreme phenotypes are expressed (without blending)

Codominance is usually seen in…

The production of proteins

Codominance examples

1.) ABO blood system

2.) MN blood system

3.) Cows

ABO blood system complete dominance

1.) A and B have complete dominance over O

2.) A and B have codominance

3.) This results in 4 phenotypes and 6 genotypes

How is your blood-type identified?

It is identified by specific antigen-antibody reactions on a microscope slide

How is your blood-type identified? (process)

1.) Place a drop of blood in anti-A and anti-B antiserum wells, which contains antibodies that recognizes carbohydrate structures on the surface of RBCs

2.) If the antibody binds to the antigen protein, it causes the RBCs to clump, indicating a positive result for the blood type

A blood type

Has the A antigen and B antibodies, therefore can only take in A or O, no B

B blood type

Has the B antigen and A antibodies, therefore it can only take in B or O, no A

AB blood types

1.) Have the antigens for both A and B, but no antibodies, therefore it can have A, B, AB, or O

2.) It is the universal recipient

O blood type

1.) It has has no A or B antigens, but it has antibodies for both, therefore it can only take in O

2.) It is the universal donor

Blood donations

The person receiving it must not contain an antibody that reacts with the donations antigens, otherwise it can cause blood clots

MN blood type system

Has M and N alleles that are also codominant, resulting in three different blood types (M, N, and MN)

MN vs. ABO blood systems

They assort independently from one another, therefore we can use separate monohybrids or a dihybrid cross to see what the genotypes of the children may be

Allelic series

It is when multiple alleles within the population are present (prime example being ABO blood types)

Dominance in allelic series

The order of dominance in the various alleles is based on the amount of protein produced when the gene is expressed

Can complete dominance, codominance, and incomplete dominance occur in allelic series?

Yes

Number of genotypes for allelic series

n(n+1)/2

Number of homozygotes in allelic series

n

Number of heterozygotes in allelic series

n(n-1)/2