Answer: number 21.
- A number 18
- B number 21
- C number 13
- D number 23
Correct answer: B. number 21
Explanation: Down syndrome (trisomy 21) results from an additional copy of chromosome 21, giving a total of 47 chromosomes.
Punnett square for a monohybrid cross between two heterozygous (Tt) parents, showing the 3:1 phenotypic ratio predicted by Mendel's Law of Segregation.
Concept context
Mendel's laws, inheritance patterns, DNA structure, and molecular biology. Core of NEET biology.
Read the full Principles of Inheritance and Variation notes →