Question

Describe in detail both
gene linked and chromosomal abnormalities that may occur.

Answer 1

GENE LINKED ABNORMALITIES

Mutations may occur in a specific gene. These changes do not affect the structure of the chromosomes and thus cannot be seen on karyotype analysis. Most common disorders are Haemophilia, Sickle cell anaemia, Color blindness, Phenylketonuria etc.

• Haemophilia - The sex linked recessive disease, which shows transmission from unaffected carrier female to some of the male progeny. A single protein that is a part of cascade proteins involved in clotting of blood is affected. As a result, a simple cut leads to non-stop bleeding.
• Phenylketonuria - This is inborn error of metabolism and is inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts amino acid phenylalanine into tyrosine. As a result the accumuled phenylalanine gets converted into phenylpyruvic acid and others. This therefore, results in mental retardation.

CHROMOSOMAL ABNORMALITIES

Such disorders are caused due to absence or excess or abnormal arrangement of one or more chromosomes. Sometimes, an additional copy of chromosome may be included in an individual (trisomy) or an individual may lack one of any pair of chromosomes (monosomy). Some of the examples are Down syndrome, Klinefelter's disease, Turner's syndrome, Patau syndrome, Edward syndrome etc.

• Down syndrome - This is caused due the presence of an additional copy of chromosome number 21(trisomy of 21). The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad. Physical and mental development is retarded.
• Turner's syndrome - This is caused due to the absence of one of the X chromosomes, i.e. 45 with X0. Such females are sterile as ovaries are rudimentary. Females also lack other secondary sexual characters.

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