X linked Recessive disorders - Colour blindness , Haemophilia Phenylketonuria Duchenne muscular dystrophy

 

• These disorders are caused by the mutations in genes on the X chromosome. 

• Female has two X chromosomes in her genetic constitution therefore two mutant genes on each X chromosome are needed to appear in these disorders.

• if one X chromosome in a female has a gene of these disorders called carrier and carrier female does not affect these disorders.

• Male has one X  chromosome and one Y chromosome so if he has a gene in a single X chromosome  of this disorder then he suffers from this  disorder.

• A daughter will be normally be colour blind when   Her mother is a carrier and her father is colour blind.

👌👌Remember- Male suffers more than female from X linked recessive disorder because male has single  X chromosome and male has two X chromosomes.

Examples of X linked recessive disorder

• In Color Blindness the affected person can not detect the colour. Affected person can not  distinguished between Red and green colour and between black and blue  color due to defect in cone cells responsible for color vision.

• Diagnosis Of Colour Blindness is done by using the Ishihara card by the Ophthalologist.

• Colour blindness was discovered by John Dalton in  Although  he was also suffering from colour blindness. Colour blindness is also called as Daltonism. 

• This disease occur completely or totally   when two or three cone cells  are absent or affected. Word Monochromy is used for totally colourblindnes.

• When only one of the cone cell  is absent or affected. This causes  partial colour blindness or Dichromy.

• In Haemophilia, bleeding is not stopped even in a minor cut or injury or we can say the process of blood clotting not occur normally. This diseased is caused by the absence of a protein needed for the process of blood clotting.

• This protein is called prothrombin that form an integral part of our cascade system. Cascade system is combined symptom of all factors required in blood coagulation.

• When the gene of  factor VIII antihemophilic factor on the X chromosome is affected due to the mutation called Hemophilia A and Hemophilia B  is caused by a mutation in the gene of  Factor IX  Christmas factor or thromboplastin on the X chromosome.

• Queen Victoria is regarded as carrier of this disorder Therefore it is called Royal  disease.

• In Phenylketonuria, the gene of enzyme phenyl alanine hydroxylase is absent or affected. This enzyme is required for the protein metabolism.

• It convert  amino acids phenylalanine into tyrosine for smooth protein metabolism. When this enzyme is absent then phenylalanine is accumulated in body and causes mental retardation intellectual disabilities, behavioural symptoms and deformities in skin pigmentation.

• Duchenne muscular dystrophy is a  muscle affected  disease that causes irregular  movement of muscles.. The disease is caused by mutations in a gene responsible for  dystrophin.

• As a result  the production of dystrophin in muscle is absent. Muscles without dystrophin causes the loss of  function of muscle and tissue.