Home › Tamil Nadu SSLC (Class 10) › Biology › Genetics › Down's syndrome in humans is caused by the prese…
Down'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_
Related questions
Plants used in Mendel's first-generation crosses were labelled the generation called:The probability of an event found by dividing occurrences by opportunities is described asA recessive disorder preventing proper metabolism of phenylalanine and tyrosine is:Ignoring seed colour, the share of a dihybrid F2 generation with round seeds is:In pea plants round seed shape is dominant over shape that is:The F2 phenotypic ratio from a standard dihybrid cross is:A cross between true-breeding parents differing in two characteristics is a:The rule that genes do not influence each other's sorting into gametes is the law of indep