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NCERT Exemplar · Class 10 Science Heredity and Evolution

47 questions · 47 still being checked

Multiple Choice Questions 21–25 (part 3 of 5)

  1. Exercise 21

    Select the statements that describe characteristics of genes
    (i)
    genes are specific sequence of bases in a DNA molecule
    (ii)
    a gene does not code for proteins
    (iii)
    in individuals of a given species, a specific gene is located on a particular chromosome
    (iv)
    each chromosome has only one gene
    (a) (i) and (ii)
    (b) (i) and (iii)
    (c) (i) and (iv)
    (d) (ii) and (iv)

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    NCERT’s answer
    (b)
    (b) (i) and (iii).A gene is a base sequence coding for protein, so (ii) is false; a chromosome holds many genes, so (iv) is false; (iii) is correct — a gene has a fixed locus.Answer: (b)

  2. Exercise 22

    In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2\displaystyle \mathrm{F}_2 is
    (a)
    1\displaystyle 1 : 3\displaystyle 3
    (b)
    3\displaystyle 3 : 1\displaystyle 1
    (c)
    1\displaystyle 1 : 1\displaystyle 1
    (d)
    2\displaystyle 2 : 1\displaystyle 1

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    NCERT’s answer
    (c)
    (c) $\displaystyle 1$ : $\displaystyle 1$ \[TT \times tt \rightarrow F_1:\ \text{all } Tt\ (\text{tall}) \] \[F_1 \times F_1 \rightarrow F_2:\ 1\,TT : 2\,Tt : 1\,tt \] Only \(\displaystyle TT\) breeds true as pure tall, so pure tall \(\displaystyle :\) short \(\displaystyle = TT:tt = 1:1\).

  3. Exercise 23

    The number of pair (s) of sex chromosomes in the zygote of humans is
    (a)
    one
    (b)
    two
    (c)
    three
    (d)
    four

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    NCERT’s answer
    (a)
    (a) one The zygote carries $\displaystyle 23$ chromosome pairs; only one pair, \(\displaystyle XX\) or \(\displaystyle XY\), determines sex, all others are autosomes.

  4. Exercise 24

    The theory of evolution of species by natural selection was given by
    (a)
    Mendel
    (b)
    Darwin
    (c)
    Morgan
    (d)
    Lamarck

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    NCERT’s answer
    (b)
    (b) Darwin Charles Darwin proposed natural selection: heritable variations that improve survival and reproduction accumulate over generations, driving evolution.

  5. Exercise 25

    Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
    (a)
    reptiles have evolved from birds
    (b)
    there is no evolutionary connection between reptiles and birds
    (c)
    feathers are homologous structures in both the organisms
    (d)
    birds have evolved from reptiles

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    NCERT’s answer
    (d)
    (d) birds have evolved from reptiles Feathers appeared first in non-flying dinosaurs (reptiles); birds inherited them and adapted them for flight, so the shared structure marks reptiles as the ancestral group.