Shape of chromosome is determined by centromere. The position of centromere is constant for a particular chromosome on the basis of its position, the chromosomes are categorised as
[a] Metacentric-The V-shaped chromosome, in which centromere lies in the middle of chromosome so that the two arms are almost equal.
[b] Submetacentric-These are J or L shaped chromosomes with centromere slightly away from the mid-point so that the two arms are unequal.
[c] Acrocentric-rod shaped chromosomes having subterminal centromere. One arm is very long and the other is very small.
[d] Telocentric-rod-shaped with centromere occupying a terminal position. One arm is very long and the other is absent.