Question

what is the reason for 21st trisomy​

Answer 1

Answer:

normally egg cell and sperm have 23 chromosome each. sometimes an error occurs and each cell keeps 2 copies of 21st chromosome instead of one. hence when these cells fertilise the zygote has 3 copies of 21st chromosome. this is called 21st triosomy or commonly known as down syndrome.

Explanation:

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