alleryDown's syndrome in humans is caused by the presence of an extra copy of which chromosome?
AChromosome 18
BThe X chromosome
CThe Y chromosome
DChromosome 21
Answer & Solution
Correct answer: D. Chromosome 21
1. Down's syndrome is an aneuploid condition with one extra chromosome.
2. The extra chromosome is a third copy of chromosome 21, called Trisomy 21.
3. This adds to the usual pair, giving three copies of chromosome 21.
4. So the affected chromosome is number 21, option D.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 18 Genetics "Down's syndrome", p.277_
Keep practising Unit 5C: Non-Mendelian Genetics & Population Transmission
Browse all Unit 5C: Non-Mendelian Genetics & Population Transmission questions for AP Biology, or explore more Biology topics.
Related questions
Which of the following is **not** a stop codon?The semiconservative nature of DNA replication was experimentally proved by:The F₂ **genotypic** ratio in Mendel's monohybrid cross is:In Mendel's monohybrid cross between true-breeding tall (TT) and dwarf (tt) plants, the F₂Mendel conducted his hybridisation experiments on which plant?In the Watson-Crick double helix, adenine pairs with thymine via how many hydrogen bonds?In birds, the sex-determination mechanism is:Down syndrome in humans is caused by