Formula for number of divisions required to form x number of cells (Mitosis and Meiosis)

Question

In case of Mitotic Division, we say that if the total number of cells formed by mitotic divisions are $x$, then counting from the first cell onwards, we get $x-1$ divisions ($N$)

$N = x-1$

This is fairly logical to me

However, to find total number of meiotic divisions for $x$ cells, we use the formula $x/4$ (In questions where we are supposed to find total number of divisions required for forming some number of seeds or pollen grains)

Shouldn't the formula be $N = (x-1)/3$ (Using the same logic as used for the mitosis formula)?

Answer 1

For a male, one primary spermatocyte produces two secondary spermatocytes through meiosis I, which in turn produce two spermatids each through meiosis II. So one primary spermatocyte produces four spermatids. That means that $x$ spermatids are produced after $x/4$ meiotic divisions consisting of once meiosis I and twice meiosis II.

However, we don't count the first cell here because a primary spermatocyte is fundamentally different form a spermatid. So in meiosis, the first cell isn't counted, and four new cells are produced.

In mitosis, we do count the first cell. Note that there are two cells produced form one, so there is only one new cell. Hence we get the formula $x-1$.