• The normal functioning of the genetic system in an organism is maintained
by the constancy of the hereditary material carried in the chromosomes.
• Each species has a constant diploid number of chromosomes, which are
in homologous pairs.
• Under various conditions, there may be changes in the karyotype
(characteristic chromosome set of a given species) with different genetic
consequences.
• Chromosomes come in pairs, with half of each inherited from each parent.
Each cell of an organism has the same number of chromosomes, except
the gametes, which have only half as many chromosomes, as the somatic
(body) cells.
• However, the size and number of chromosomes varies among species.
• Chromosomes may change in number maintaining a normal structure, or
they may have structural alterations, frequently called chromosomal
mutations or chromosomal aberrations.
• This process occurs generally during the formation of a zygote, where
changes in the number of chromosomes may result in fission (breaking
of one chromosome into two) or fusion (joining of two chromosomes
into one).
• Such structural changes may appear spontaneously, or they may be
caused by the action of ionizing radiations or by chemicals.
• Chromosome mutations are different from gene mutations, in that a
spontaneous modification results in more pronounced effects.
Chromosomal Mutations
Class XII
Analysis of various PMTs from 2009-2014
2009
2010
2011
2012
2013
2014
AIPMT/NEET
1
1
1
1
1
AIIMS
1
AMU
1
1
1
1
Kerala
1
4
1
1
K.CET
1
1
1
J & K
BHU
4
2
