Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
NEET2013ZoologyPrinciples of Inheritance and VariationActual

Down's syndrome in humans is due to:

Options

  1. Athree ' X ' chromosomes
  2. Bthree copies of chromosome 21
  3. Cmonosomy
  4. Dtwo ' Y ' chromosomes.

Correct answer

B. three copies of chromosome 21

Step-by-step solution

Down's syndrome a genetic disorder is due to the presence of an extra chromosome 21 also known as trisomy of chromosome 21 . Related Theory Down's syndrome is caused due to abnormal cell division. During mitotic and meiotic cell division the chromosome pair separate so that each cell gets the copy of each chromosome. In Down syndrome, the chromosomes are not able to separate, giving rise to cells with an unequal number of chromosomes (nondisjunction).

Practice Principles of Inheritance and Variation on Quantrex Academy →

More from Principles of Inheritance and Variation

Match List I with List II : List I List II A. Incomplete dominance I. Human skin colour B. Co-dominance II. Inheritance of flower colour in Antirrhinum sp. C. Pleiotropy III. Pheny 2026The sixth mutant codon of beta globin gene causing polymerization of Haemoglobin and change in RBC shape is : 2026In a population of a grasshopper species, the chromosome number of some members is 23 and some other members possess 24 chromosomes. The 23 and 24 chromosome-bearing members in thi 2026Which one of the following disorders is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule 2026What is the probability of having children with 'O' blood group, where both mother and father are heterozygous for 'A' and 'B' blood group, respectively ? 2026Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R . Assertion A : In an experiment, Mendel observed that the F1 progeny plants a 2026Given below are two statements : Statement I : Down's syndrome is caused by the absence of one of the X-chromosomes. Statement II : Turner's syndrome is caused by the presence of a 2026Which of the following statements are true with reference to the sex-determination in honeybees ? A. An offspring formed from the union of a sperm and an egg, develops as a female 2026 Full Principles of Inheritance and Variation list All NEET PYQs