euploidy
• The organisms having one or more complete sets
of chromosomes, or organisms having chromosome
number which is whole number multiple of basic
chromosome number, are called euploids and this
phenomenon is called euploidy.
• For example, if basic chromosome no. x = 7. Then,
• Euploidy maybe of the following types:
haploidy and monoploidy
• Haploids are the individuals, which are having half
the chromosome number (somatic), as compared to its
diploid or normal individual, e.g., in wheat,
2 n = 6x = 42 (Hexaploid wheat)
Thus, 2 n = 3x = 21 (Haploid)
• Monoploids, on the other hand, are the individuals
having single basic set of chromosomes, e.g. in barley,
2 n = x = 7 (Monoploid), in maize, 2 n = x = 10
(Monoploid). (Here x is the basic chromosome
number).
• In haploids, there is reduction in size of vegetative
and reproductive parts (e.g., stomatal size, pollen size
and seed size, etc.)
• Best method of haploid production is pollen
culture.
• Haploids are very useful in studies of mutation, because
a minute change can be detected in them, due to the
presence of a single set of chromosomes.
• Secondly, by doubling their chromosome number by
colchicine treatment, homozygous diploids are
produced, which are used as new varieties, or used as
one of the parents in hybridization experiments.
Polyploidy
• A plant or animal
that has more than
two haploid sets
of chromosomes
i s c a l l e d a
polyploid. This
change is common
in nature, especially
in the flowering
plants.
• A diploid organism has two similar genomes, a triploid
has three, a tetraploid has four, and so on.
• Polyploids may originate either by reduplication
of the chromosome number in somatic tissue, with
suppression of cytokinesis, or by formation
of gametes with an unreduced number of
chromosomes.
• Meiosis in a triploid is more irregular, than in a
tetraploid.
• In general, polyploids of uneven number are sterile,
because the gametes have unbalanced number of
chromosomes.
• The scarcity of polyploids among animals is due to the
mechanism by which sex is determined.
• If polyploidy occurs, the genic balance between the
sex chromosomes and the autosomes is disturbed,
and the race or species may disappear, because of
sterility.
• Polyploid types are according to the number of
chromosome sets in the nucleus :- Triploid (three sets; 3x), for example, subphylum
Tardigrada. - Tetraploid (four sets; 4x), for example, Salmonidae
fish. - Pentaploid (five sets; 5x)
- Hexaploid (six sets; 6x), for example, wheat,
kiwifruit. - Octaploid (eight sets; 8x), for example, Acipenser
(genus of sturgeon fish). - Decaploid (ten sets; 10x), for example, certain
strawberries. - Dodecaploid (twelve sets; 12x), for example, the
plant Celosia argentea and amphibian Xenopus
ruwenzoriensis.
Polyploidy in plants
• Polyploidy is pervasive in plants, and some
estimates suggest that 30-
80% of living plant species
are polyploid, and many
lineages show evidence
of ancient polyploidy
(paleopolyploidy) in their
genomes.
• Huge explosions
in angiosperm species
diversity appear to have
coincided with the timing