Co-Dominance/Multiple Alleles

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Till now we have seen that the F1 generation resembles either of the two parents and not both. However, in co-dominance, the F1 generation resembles both parents. The human blood group is an excellent example of co-dominance. The ABO blood groups are controlled by a single gene I, but it has multiple alleles (IA, IB, and i). RBC with allele 'i' does not possess  any sugar polymer on its surface.

The plasma membrane of the RBCs contains sugar polymers, and the kind of sugars is controlled by the gene. Since humans are diploid, each person contains any two alleles. For example, an offspring will possess a blood group A when both of his/her parents possess IA allele. 

Following are the possible blood type combinations:



These are the possible combinations of blood types. 









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PEDIGREE ANALYSIS: PRACTICE PROBLEMS

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https://youtu.be/4nfdm6hT-r8

Q1. Identify the inheritance pattern in the following picture.


The above pedigree is Autosomal recessive. 

  • Recessive because there is skipping of generation.
  • Autosomal recessive because, it does not fulfill X-linked recessive condition.

For X-linked recessive, following conditions must be fulfilled:
  1. More boys affected than girls
  2. Female does not affect female
  3. Affected mom has to have affected sons as well as dad

Q2. Identify the mode of inheritance.
The above pedigree is X-linked dominant because of the following reasons:

 1. Dominant because there is no skipping of generation.
2. X-linked dominant condition must follow DDD rule (the first D represents dominant condition; the second D represents affected D; the third D represents daughters). It means, in a dominant condition, if dad is affected, all his daughters will be affected too.
3. The above pedigree follows DDD rule.


Q3. Identify the mode of inheritance.

Autosomal dominant

No DDD rule followed in the above pedigree

Q4. Identify the pattern of inheritance.


Autosomal recessive

No X-linked recessive condition followed.

Q5. Identify the pattern of inheritance.

X-linked recessive

Followed X-linked recessive condition.
It is recessive because two unaffected parents produced affected offspring -- a characteristic of recessive trait. 


Q6. Find the pattern of inheritance in the following pedigree and write the genotype of III 7


 Q7. Find the pattern of inheritance and the genotype of the parents

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