Download App

STD 12 - 4. principal of inheritance and variation — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYSTD 12 - 4. principal of inheritance and variation1 Mark
MCQ
Down’s syndrome in humans is due to
  • A
    three $‘X’$ chromosomes
  • ✓
    three copies of chromosome $21$
  • C
    monosomy
  • D
    two $‘Y’$ chromosomes.
✓

Answer

Correct option: B.
three copies of chromosome $21$
b
(b): Down’s syndrome is the trisomy of $21$ stchromosome in man. Down’s syndrome ischaracterized by short stature, warty skin, protrudingtongue, slanting eyes, with folded eyelids. The affectedperson’s face presents a typical mongoloid look. Henceit is also called as mongoloid idiocy. It occurs due tothe phenomenon of nondisjunction.Non disjunction occurs when a pair of homologous chromosomes donot separate in meiosis but migrate to the same poleof the cell resulting in an uneven number ofchromosomes in the daughter cells $(45$ in one and $47$ in other) This numerical abnormality results in trisomy $(2n + 1)$ and monosomy $(2n -1)$. Nondisjunctionismore common in sex chromosomes.

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "M.C.Q (0.5 Marks)" from STD 12 - 4. principal of inheritance and variation→STD 12 - 4. principal of inheritance and variation — all question types→BIOLOGY STD 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

Darwin's theory of natural selection to explain organic evolution was based on
→
$A$ : Myocardial infarction can now be treated more effectively due to genetic engineering.

$R$ : Streptokinase produced by Streptoccocus and modified by $RDT$ is used as a clot buster for removing thrombus

→
Which of the following immunoglobulins does constitute the largest percentage in human milk ?
→
Which of the following sexually transmitted diseases is caused by a protozoan?
→
Ecosystem is defined as
→
Tuberculosis is transmitted by
→
Who discovered, sex chromosome, Y chromosome?
→
In human female the fertilized eggs gets implanted in uterus
→
The possible beneficial affect of grazing animals is the:
→
In bacteria, fungi and lower plants, various of thick-walled ...$A$... are formed, which help them to survive ...$B$... conditions-these germinate on availability of suitable environment. In higher plants ...$C$... and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal-they germinate to form new plants under favourable moisture and temperate conditions

Choose the correct option for $A, B$ and $C$

→