Practice question

Trisomy symbolizes addition single chromosome to normally diploid set, formula 2n+1 where n haploid number and 2n diploid. Humans n=23 so 2n=46 diploid, trisomy results 47 chromosomes total observable karyotype. Extra copy creates gene dosage triplication, often disrupts development via altered protein ratios and regulatory imbalance. Viable human autosomal trisomies limited to chromosomes 13,18,21 with increasing gene content correlating decreasing viability and severity. Origin usually maternal meiotic nondisjunction generating disomic gamete fertilized by normal haploid gamete, producing conceptus with extra chromosome.