Let $p$ be a prime number, and let $\mathbb{F}_{p}$ be a finite
field of order $p$. Let $GL_{n}(\mathbb{F}_{p})$ denote the general linear
group and $U_{n}$ denote the unitriangular group of $n\times n$ upper
triangular matrices with ones on the diagonal, over the finite field $%
\mathbb{F}_{p}$. In fact $U_{n}$ is a Sylow $p$-subgroup of $GL_{n}(\mathbb{F}_{p})$ of order $p^{\frac{n(n-1)}{2}}$. Given $n_{p^{2}}$ be the number of elementary abelian p-subgroups of rank $2$ in $U_{n}$. How can we deduce the number of elementary abelian p-subgroups of rank $2$ in the whole linear group $GL_{n}(\mathbb{F}_{p})$?.
Conversely, given $N_{p^{2}}$ be the number of elementary abelian p-subgroups of rank $2$ in $GL_{n}(\mathbb{F}_{p})$. Is there a criterion deduces the number of elementary abelian p-subgroups of rank $2$ in $U_{n}$?.
In other words, what is the relationship between $N_{p^{2}}$ and $n_{p^{2}}$?.
Any help would be appreciated so much. Thank you all.