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Question : Describe chromosomal disorder and describe its examples.

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Solution :The chromosomal disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes.
= Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s) called aneuploidy.
=For example Down.s syndrome results in the gain of extra copy of chromosome 21.
= Similarly, Turner.s syndrome results due to loss of an X-chromosome in human females.
=Failure to cytokinesis after telophase stage of cell division result in an increase in a WHOLE set chromosomes in an organism and this phenomenon is known as polyploidy.
=This condition is often seen in plants. The total number of chromosomes in a normal human cell is 46 (23 pairs).
=Out of these 22 pairs are autosomes and one pair of chromosomes are sex chromosome.
= Sometimes, though rarely either an additional copy of a chromosome MAY be included in an individual or an individual may lack one of any one pair of chromosomes. These SITUATIONS are known as trisomy or monosomy of a chromosome respectively.
= Such a situation leads to very SERIOUS consequences in the individual. Down.s syndrome, Turner.s syndrome, Klinefelter.s syndrome are common examples of chromosomal disorders.
= Sub Que : Describe Down.s Syndrome.
= The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21).
= The disorder was first described by Langdon Down (1866). The affected individual is short statured with SMALL round head, furrowed tongue and partially open mouth.

= Sub Que : Describe Klinefelter.s Syndrome.
=Klinefelter.s syndrome is caused due to the presence of an additional copy of Xchromosome resulting into a Karyotype of 47, XXY.

=Diagrammatic representation of genetic disorders due to sex chromo some composition in humans: (a) Klinefelter Syndrome (b) Turner.s Syndrome
=Such an individual has overall masculine development however the feminine development (development of breast, i.e. Gynaecomastia) is also expressed. - Such individuals are sterile.
=Sub Que : Describe Turner.s Syndrome.
=Turner syndrome is caused due to the absence of the X-chromosomes i.e. 45 with XO.
=Such females are sterile as ovaries are rudimentary besides other features including lack of other secondary sexual characters.


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