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Heredity and Evolution — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceHeredity and Evolution1 Mark
MCQ
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : ln humans, male $($or father$)$ is responsible for sex of the baby which is born.
Reason : $Y$ chromosomes are present in only male gametes or sperms.
  • ✓
    Both $A$ and $R$ are true, and $R$ is correct explanation of the assertion.
  • B
    Both $A$ and $R$ are true, but $R$ is not the correct explanation of the assertion.
  • C
    $A$ is true, but $R$ is false.
  • D
    $A$ is false, but $R$ is true.
✓

Answer

Correct option: A.
Both $A$ and $R$ are true, and $R$ is correct explanation of the assertion.
In humans, sex is determined by sex chromosomes. A male has one $X$ and one $Y$ chromosome $(XY)$. A female has two $X$ chromosomes $(XX)$. Male produces two types of sperms, one with $X$ and one with $Y$ whereas female produces only one type of egg with $X$ chromosome. When sperm with $X$ chromosome fertilises egg then zygote has both $XX$ chromosomes and develops into female progeny. If sperm with $Y$ chromosome fertilises egg then zygote has $XY$ chromosomes and develops into male progeny.

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