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Arjun Nagpal
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Asked: 2020-10-20T12:28:22+00:00 In:

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

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NCERT Solution for Class 10 Science Chapter 9
Heredity and Evolution
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-147
Questions No-3

2020-2021cbsechapter 9class10heredity and evolutionncertscience
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    6 Answers

    1. The information provided is not sufficient to determine which blood group trait (A or O) is dominant. The ABO blood group system is inherited through multiple alleles, and the determination of dominance is not solely based on the blood types of the parents and offspring.

      In the ABO blood group system, there are three main alleles: A, B, and O. The A and B alleles are codominant, while the O allele is recessive. The possible combinations of alleles that result in the ABO blood groups are:

      » Blood Group A: AA or AO (codominant)
      » Blood Group B: BB or BO (codominant)
      » Blood Group AB: AB (codominant)
      » Blood Group O: OO (recessive)

      Given that the daughter has blood group O, it means that both parents must have contributed an O allele. The father with blood group A could contribute either an A or an O allele, and the mother with blood group O would contribute an O allele. Therefore, the father could be AO or AA.

      The information about the daughter having blood group O only tells us about the recessive phenotype (OO), but it does not provide information about the dominant phenotype in the father. It could be either blood group A (if the father is AO) or blood group O (if the father is AA).

      In summary, based on the information provided, we cannot determine the dominance relationship between blood group A and O. Additional information about the genotype of the father is needed to make a conclusive determination about dominance.

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    2. This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.

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      • The given information is not enough to determine the traits- blood group A or O is dominant.
      • In ABO blood grouping blood type A is always dominant whereas, the blood type O is always recessive.
      • Here the father’s blood group is A hence,  it can either be homozygous (AA) or heterozygous (AO).
      • The mother’s blood group is O and it is only possible if it is heterozygous (OO).
      • For the daughter to have blood group O the father must be heterozygous (AO) and mother must be (OO).
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    4. No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. This is because we do not know about the blood group of all the progeny.
      Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.

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    6. This information is not enough. This is because each individual is carrying two alleles. The recessive trait can occur only when who alleles are similar. It blood group A is dominant and O is recessive, then daughter can have blood group O only when both recessive alleles occur together in mother, and father has one allele of O and other of A.

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    7. No. This information is not sufficient to determine which of the traits – blood group A or
      O – is dominant. This is because we do not know about the blood group of all the progeny.
      Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw
      any such conclusion.

      For more answers visit to website:
      https://www.tiwariacademy.com/ncert-solutions/class-10/science/chapter-9/

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