BOTANY Higher Secondary Second Year - Textbooks Online

Translocation
It is a kind of a chromosomal abnormality in which the interchange
of the chromosomal segments occurs. When translocation occurs between
two non-homologous chromosomes, then it is called reciprocal
translocation or illegitimate crossingover. It is of two kinds -
heterozygous translocation and homozygous translocation.
In heterozygous translocation, one member of each pair of chromosomes
is normal and the other member is with interchanged segment. But in
homozygous translocation, both the members of paired chromosomes have
translocated segments.
They play an important role in species differentiation. Translocations
causes hereditary disorders.
Numerical chromosomal aberrations
Each species of an organism has a specific number of chromosomes
in its somatic cells. These chromosomes are found in pairs. At the time of
formation of gametes the chromosome number is reduced. Hence, the
gemetes carry haploid set of chromosomes. Alterations in the number of
chromosomes from the diploid set is called numerical chromosomal
aberration. It is also known as ploidy. There are two types of ploidy –
euploidy and aneuploidy.
Euploidy
Euploidy is the variation in the chromosome number that occurs due
to increase or decrease of full set of chromosomes. Monoploidy, diploidy
and polyploidy are the types in euploidy.
Diploidy
In most of the plants and animals, the somatic cells contain two sets
of chromosome. Diploidy is formed by the union of two gametes during
fertilization.
Polyploidy
Addition of one or more sets of chromosomes to the diploid set results
in polyploidy. It is commonly noticed in plants and rare in animals. They
are of two kinds – autopolyploidy and allopolyploidy.
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