Down syndrome (trisomy 21) results from
- A
Loss of one X chromosome producing a gamete with 22 chromosomes total
- B
A point mutation in a single gene on chromosome 21 during DNA replication
- C
Crossing over between non-homologous chromosomes during prophase I of meiosis
- Dcheck_circle
Nondisjunction of chromosome 21 during meiosis, producing a gamete with 24 chromosomes
Explanation
Three copies of chromosome 21 in the zygote (47 total chromosomes).