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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation5 Marks
Question
  1. List the three different allelic forms of gene ‘I’ in humans. Explain the different phenotypic expressions, controlled by these three forms.
  2. A woman with blood group'A'marries a man with blood group 'O'. Discuss the possibilities of the inheritance of the blood groups in the following, starting with 'yes' or 'no' for each:
  1. They produce children with blood group ‘A’ only.
  2. They produce children, some with 'O' blood group and some with 'A' blood group.
✓

Answer

  1. Inheritance of human blood-group character:
  • The gene for blood group character exists in three allelic forms, $I^A, I^B$ and i; it is a case of multiple allelism.
  • The phenotypes and genotypes of these alleles are as follows:
Blood group
Genotype(s)
A
$I^AI^A$ or $I^Ai$
B
$I^BI^B$ or $I^Bi$
AB
$I^AI^B$
O
ii
  • The alleles $I^A$ and $I^B$ are codominant and express themselves as blood group AB, when they are together.
  • Blood group O is homozygous recessive.
  1.  
  1. Yes, when the woman is homozygous $(I^AI^A)$ for blood group A, the children can be with only blood group A,

Or
No, When the woman is heterozygous $(I^Ai)$ for blood group A, children will be of A group and O group.
  1. Yes, when the woman is heterozygous $(I^Ai)$ for blood group A, children can be with either blood group A or O (as in the cross above).
    Or
    No, when the woman is homozygous $(I^AI^A)$ for blood group A, the children can be with only blood group A (as in the first cross of (i) of this answer).

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