Which of the following are used to define the karyotype of a species?
$1$. The number of chromosomes
$2$. The chromosome length
$3$. The positions of the centromeres

• A
  $1$,$2$ and $3$ are correct
• B
  Only $1$ and $2$ are correct
• C
  Only $2$ and $3$ are correct
• D
  Only $1$ and $3$ are correct