A number of disorders in human beings have been found to be associated with the inheritance of changed or altered genes of chromosomes.
Genetic disorders broadly grouped into two categories :
(1) Mendalian disorders, (2) Chromosomal disorders
I) Mendelian disorders : These are genetic disorders showing Mendelian pattern of inheritance, caused by a single mutation in structure of DNA.
Most common and prevalent Meridelian disorders are: Haemophilia, Cystic fibrosis, sickle cell anaemia, colour blindness, phenyl ketonuria, thalassemia etc., I. Haemophilia : It is also called as bleeder.s disease. (a) Haethophilin• : This is sex linked recessive disorder, transmitted by females arid affecting males.
Haemophilia-A is the most common clotting abnormality and is due to the deficiency of clotting factor VIII.
Symptoms : The affected individuals haye prolonged clotting time and suffer from internal bleeding.
Haemophilia (B) : This is due to the deficiency of clotting factor IX.
symptoms : Symptoms are similar In that found in haemophilia-A.
II Sickle-cell anaemia : It is an autosomal recessive genetic disorder, characterised by rigid, sickle-shaped red blood cells In hypoxia condition. It is due to point mutation in the fl-globin gene causing replacement of glutamic acid in the sixth position by valine.
Symptoms : Haemolysis leads to sickle-cell anaemia sickle cells block. The capillaries resulting in poor blood supply to tissue leads to physical weakness, pain, organ damage, paralysis etc.,
III. Phenyiketonhrla : This is an autosomal recessive metabolic genetic disorder caused by a mutation in the gene codes for phenylalanine hydroxylase. This enzyme catalyses the convertion of phenyialanine into tyrosine. Defect of this enzyme leads to accumulation of .phenylalanine derivatives like phenylpyruvate, phenylacetate etc.,
Symptoms : Mental retardation, failure to walk or talk, failure of growth etc.,
IV.Colour blindness : It is a sex linked .disorder. It is the inability to differentiate between some colours. This phenotypic trait is dumb mutation in certain genes located in X-chromosome.
Symptotas Protartopia - red colour blindness
Deuteronopia - green colour blindness
Tritanopia - blue colour blindness
V. Thalassemia : Thalassemia is an autosome linked recessive blood disorder. Thalassemia are characterised by a defect in the a or # Globin chain, resulting in production of abnormal haemoglobin molecules lea. to anaemia. Symptomps : Anaemia
VI. Cystic fibrosis : It is an autosornal recessive genetic disorder. It is the result of mutation the gene that influences salt and water movement across epithelial cell membrane.
Symptoms : The mucus builds up in organs such lungs, pancreas, GI tracts etc., If they are not treated it may lead to death.
2. Chromosomal disorders Chromosomal disorders are caused by errors in the number or structure of chromosome.
Allosomal disorders :
I. Klinefelter.s syndrome : This genetic disorder due to the presence of additional chromosome along with. the normal XY.
Symptoms : The remitting young sterile male shows feeble. breast, small testicles, rounded hips etc.,
II. Turner.s syndrome : A female with 44 autosomes with one X-chromosome, such females are sterile.
Symptoms : Short structure, webbed neck. broad shield chest with widely spaced nipples., poorly developed ovaries etc.,
Autosomal disorders :
I. Down syndrome( Trisomy 21) : The cause of this genetic disorder is the presence of an additional copy of chromosome numbered 21:
Symptoms Small rounded head, furrow. tongue and partially open mouth mental retardent etc.,
IL Edwards syndrome (Trisomy 18) : This is due to presence-of an extra copy of genetic material on the 18th chromosome, either in whole or a part.
Symptoms : Majority of people with the syndrome die during the foetal stage due to defect in heart and kidney.
III. Patau syndrome (Trisomy 13) Palau syndrome is .due to Presence of an addition copy of chromosorne number 13.
Symptoms : Kidney and heart defects, intellectual disability etc.,
