Genetic Disorders ||Class 12 Biology

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    A number of disorders in human beings, are associated with the inheritance of changed and altered genes or chromosomes. These are called genetic disorders.  Since, it is not possible to perform control crosses in humans, study of family history about inheritance of a particular trait provides an alternative in the diagnosis of genetic disorders or abnormalities.
      The genetic disorders can be classified as: 
1. Mendelian disorders or Gene-related disorders
2. Chromosomal disorders

1. Mendelian disorders or Gene-related disorders: These are the disorders that are mainly determined by alterations or mutation in the single gene. These disorders are transmitted in the next generation according to the principle of inheritance and can be studied by the pedigree analysis. The diseases may occur as dominant or recessive. Example: Haemophilia, colour blindness, sickle-cell anaemia, phenylketonuria etc.

2. Chromosomal disorder: These are caused by the absence or excess or abnormal arrangement of one or more chromosomes. The Chromosomal disorders can be studied by the analysis of karyotypes. Example: Down's Syndrome, Turner's syndrome, Klinefelter's syndrome.







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