Sex Linked Diseases


 
 
Concept Explanation
 

Sex Linked Diseases

Sex linked is a trait in which a gene is located on a sex chromosome. In humans, the term generally refers to traits that are influenced by genes on the X chromosome. This is because the X chromosome is large and contains many more genes than the smaller Y chromosome. In a sex linked disease, it is usually males who are affected because they have a single copy of X chromosome that carries the mutation. In females, the effect of the mutation may be masked by the second healthy copy of the X chromosome.

'X' Linked inheritance :

Certain disorders caused due to heredity such as haemophilia and colour blindness are more common in males than in females. Such defects are due to recessive genes, which occur on the 'X' chromosome. 

Haemophilia is a genetic disorder in which the sufferers are at a risk of bleeding to death because the blood fails to clot in them. Rare cases of haemophiliac males do occur but practically, none of haemophilic females.

The following cases explain the sex linked in humans.

Case I

                  Normal mother  X   Colour blind father

                       

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Case II

Carrier mother  X  Normal father

Case III

Colour blind mother  X   Normal father

Y linked inheritance

The Y chromosome linked traits occur in males but not in females. for eg :- traits such as hypertrichosis of ears and pattern baldness are found in men only.

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