what does having an extra chromosome
Babies born with trisomy 21, or an extra chromosome 21, have a condition known as Down Syndrome. Although children with Down Syndrome do suffer form some level of mental retardation, the majority of them are high-functioning.op 10 unbelievable historical concurrencies. Someone who has an extra chromosome has 47 total chromosomes instead of the typical 46, or 23 from each parent. This results in a condition known as trisomy.