Why do we abbreviate trisomy as n + 1?

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Answer 1 · 2017-10-10T18:20:01

Here's the reason.

Firstly I would like to throw some light that $n + 1$ $n+1$ is not an abbreviation of trisomy.

General abbreviation of trisomy is $2 n + 1$ $2n+1$ .

$n$ $n$ is the haploid number of chromosomes at a certain sequence.

Now, it's diploid is $2 n$ $2n$ .

Now, haploidy & diploidy are common intermediates of chromosomes.

But, an abnormal count of chromosomes is called aneuploidy.

Some aneuploid conditions are $\to$ $rarr$

(1). $2 n - 1$ $2n − 1$ $\to$ $rarr$ monosomy.
(because only one copy of same specific chromosome is present).

(2). $n + 1$ $n+1$ $\to$ $rarr$ disomy.
(because two copies of same specific chromosome is present).

(3). $2 n + 1$ $2n + 1$ $\to$ $rarr$ trisomy.
(because three copies of same specific chromosome is present).

(4). $2 n - 2$ $2n − 2$ $\to$ $rarr$ nullisomy.
(because no copy of a specific chromosome is present).

Hope it Helps:).