In next few slides we are going to understand the concept of codominance. In this case, expression of both alleles of heterozygote occur.

1. Codominance
Presented by:
Sanjay Kr. Vishwakarma

2. Codominance
• Two alleles of a single gene are responsible for producing two distinct, detectable gene
products
• The joint expression of both alleles in a heterozygote is called codominance
• Heterozygote will be phenotypically distinguishable from both of the homozygotes
• Expressing both alleles equally

3. Example
• MN blood group antigens are a good example
• The MN system is under the control of a locus found on chromosome 4,
with two alleles designated LM and LN
• Three combinations are possible, each resulting in a distinct blood type:

4. • Allele LM for M-type blood is codominant with its allele LN for
N-type blood
• Heterozygote (LMLN) expresses the characteristics of both M
and N antigens (MN-type blood)
• Red blood cells carry both M and N antigens on its surface
• Two alleles encode nonidentical protein products

5. • Mating between a homozygous M-type person (LMLM) and a
homozygous N-type person (LNLN) produce all heterozygous
(LMLN) offspring

6. • Mating between two heterozygous MN (LMLN X LMLN) parents may
produce children of all three blood types, as follows:
• Ratio is 1 M-type (LMLM) : 2 MN-type (LMLN) : 1 N-type (LNLN)
• Expression of both alleles in heterozygotes demonstrate the codominant
nature of alleles

7. Multiple Choice Question

8. 1) An M blood type daughter is born to a mother who has type M blood group and a
father who has type N. Which of the following is true?
a) The father of the child is someone else
b) The mother of the child is someone else
c) This is a normal case
d) The child has genotype M/N
Answer: a

9. 2) In case of codominance, product is
a) Produced from both the alleles
b) Produced from one allele
c) Incompletely produced from both alleles
d) None are functional
Answer: a

10. 3) A gene for corn has two alleles, one for yellow kernels and one for white kernels.
Cross pollination of yellow corn and white corn results in ears of corn that have an
approximately even mix of yellow and white kernels. Which term best describes the
relationship between the two alleles?
a) Genetic recombination
b) Codominance
c) Incomplete dominance
d) Chimerism
Answer: b

11. Thank You