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Genetic Disorders - Duchenne Muscular Dystrophy

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Science Report

Genetic Disorders- Duchenne Muscular Dystrophy (DMD)

Description of disorder, symptoms and chance of survival

Duchenne muscular dystrophy is a genetic disorder that causes 1 out of 3500 males' voluntary muscles that control their body's movement to progressively weaken and waste due to a lack of dystrophin. Dystrophyn is an important muscle protein which is produced in a gene in the X chromosome. Hence, it is a sex linked disorder that affects only boys. The boy, if he inherits the disorder, looses muscle throughout his life. Symptoms include; tightening of muscles, difficulty in walking/running and calves may be large and firm. If inherited, the boy will not survive as the condition will make him become disabled due to his voluntary muscles progressively weakening and wasting.

Example of pedigree diagram for inheritance of disorder and how diagram provides clues as to how the condition is inherited

The previous diagram shows that DMD is due to a recessive, sex (X) linked gene inherited by the grandmother because if the grandparents (1 and 2) reproduce their alleles must look like the diagram below and 25% of their children should have the condition. It is inherited by the grandmother because if it was inherited by the grandfather the punnet square would not have a male with DMD.

When the grandparents reproduced the condition could not be inherited by the male (1) because due to the previous punnet square, the female (2) is the carrier while the male only passes the XY gene over to his female children .....

...which, if 3 and 4 reproduce they have a 25% chance

of having a boy with DMD as show to the right.

In the pedigree diagram I have analysed each person who has children with the disorder to determine that their mother is the carrier (as it is a sex [X carried] linked disorder) hence I have determine each person's genotype below:

1. XY 4. 7. XX 10. 13. XY

2. 5. XY 8. XX 11. 14. XX

3. XY 6. 9. 12. XY

Explanation of how predictions of the condition occurring in future generations can be made using a diagram (Punnet Square) including explanation of Alleles

All humans inherit sex chromosomes from their parents which determine their sex. Males have XY chromosomes in their gametes while females have XX chromosomes in their gametes.

The condition, DMD , occurs in the X chromosome on a mutated gene that produces dystrophin. It is not on the Y chromosome because it does not produce dystrophin. Hence the boy after inheriting the condition can only make dystrophin from the mutated gene from his mother. This is when the boy inherits a from his mother and a from his father. Females, even though they have the mutated X gene, do not get the condition (except on rare occasions) because their other X gene



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