Introduction

In the vast majority of cases, when a zygote contains an incorrect number of chromosomes as a result of a gamete produced through meiosis in which a nondisjunction event occurred, that zygote will be non-viable and will be spontaneously aborted.  However, in rare instances, a zygote can survive and develop into a fetus, such as is the case with Down Syndrome.

Let us explore how this occurs now.

The following video explains Klinefelter (XXY) and Turner Syndromes (XO).

Summary

In this section, we have learned:

• In rare instances, a zygote containing an irregular number of chromosomes can survive and develop.
• In Down Syndrome, an individual inherits (3) copies of Chromosome #21, a condition also referred to as ‘Trisomy 21‘
• Nondisjunction of the sex chromosomes can result in the inheritance of too few or too many sex chromosomes. Not all permutations are viable and/or fertile.

Sources:

“Klinefelter (XXY) & Turner Syndrome.” By Lecturio Medical, May 6, 2019. Retrieved from: https://youtu.be/4_8nmveyl1A, Licensed under: CC (applicable license here)