Zoology - Principles of Inheritance and Variation Question with Solution | TestHub

Down's syndrome $(45+\mathrm{XX}$ or $45+\mathrm{XY})$ is the case when there is one extra chromosome in 21st pair of autosome. It is also called trisomy 21 or trisomy-G. It is most common in children of over aged mothers (above 41 years). It is also called Mongolian syndrome.