A woman has Charcot-Marie-Tooth (CMT) disease, which she inherited from her moth

Question

A woman has Charcot-Marie-Tooth (CMT) disease, which she inherited from her mother. CMT disease is an X-linked, dominant disease. The woman's father has Haemophilia A, which is an X-linked recessive disease. Both diseases show complete penetrance. The woman has just had twins, a boy and a girl. The father of the children has neither disorder. The genes for the two disorders are known to be 20 cM apart. a) What is the probability that the boy will have neither disorder? Explain your answer. b) What is the probability that the girl will have CMT disease but not have Haemophilia A? Explain your answer.

Explanation / Answer

Girls are carieer of X linked disease, several X-linked recessive genetic disorders like hemophilia, muscular dystrophy which are inherited through a genetic defect on an X chromosome. A female has 2 X chromosomes, one from her mother and another from her father. A male has an X chromosome from his mother and a Y chromosome from his father. Females may get the defective gene either from her mother's defective X, or, if her father has the disorder, from her father. In either case, the girl will be a carrier and will probably pass the defect to her offspring. She will not manifest the disorder the way a boy would, because she has 2 X chromosomes, and the dominant X will compensate for the defect on the recessive X.

Ques 1 As a boy gets its X chromosome from his mother there are changes that he should be effected from CMT but he will not be effected from hemophilia A as he will get Y chromosome from his father and hemophiliaA is X linked disease . But 50% he will be effected from CMT as this is X linked disease .woman with an X-linked dominant disorder has a 50 percent chance of having an affected daughter or son with each pregnancy.

Ques 2:-, the sons of a man with an X-linked dominant disorder will not be affected, but all of his daughters will inherit the condition. So there are no changes that girl will not be effected by Haemophilia. As a girl gets its one X chromosome from his mother so there are 50% chance of CMT but second X she gets from her father so there are 100% chance she will be effected by the disease which her father have

Note :- All daughters of an affected father will also be affected but none of his sons will be affected (unless the mother is also affected). In addition, the mother of an affected son is also affected (but not necessarily the other way round).

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