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Question

In humans, the sex of the baby is determined:


A

at the time of implantation and by the maternal gamete

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B

at the time of implantation and by the paternal gamete

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C

at the time of fertilization and by the maternal gamete

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D

at the time of fertilization and by the paternal gamete

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Solution

The correct option is D

at the time of fertilization and by the paternal gamete


The correct option is option D.

Explanation for correct option:

  1. Sex of the baby is determined at the time of fertilization as during this time the sperm from the male and the ovum from the female fuse with each other.
  2. Women are homogametic and produce one type of ovum (maternal gamete) (22+X).
  3. However the male companion is heterogametic and produces two types of sperm (paternal gamete) i.e. one 22+X and the other 22+Y in identical amounts.
  4. Therefore the zygote would be off (44+XX or 44+XY) chromosomes depending on which kind of sperm fertilizes the ovum.
  5. The zygote carrying 44+XX chromosomes would be a male baby whereas the other carrying 44+XY would be a female baby.
  6. Therefore the sex of the baby is determined by the paternal gamete and not by the maternal gamete at the time of fertilization.

Explanation for incorrect options:

Option A:

  1. Implantation happens while the blastocyst attaches to the endometrium of the uterine wall and happens 5 days after fertilization.
  2. During this time already the maternal gamete has fused with the paternal gamete and carries both maternal and paternal gamete.

Option B:

  1. Implantation happens when the blastocyst attaches to the endometrium of the uterine wall and happens 5 days after fertilization.
  2. During this time already the maternal gamete has fused with the paternal gamete and contains both maternal and paternal gamete.

Option C:

Maternal gamete carries only one type of ova (22+X). It does not contain the Y chromosome hence it cannot be used to determine the sex of the baby.

Final Answer: In humans, the sex of the baby is determined at the time of fertilization and by the paternal gamete.


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