I got question about sex-linked genes?

I don't know how to do this.. Please Help~





Duchenne muscular dystrophy is caused by a sex-linked recessive allele. a man who suffers from this disease, marries who does not have the disease. a woman’s father, however, did have Duchenne muscular dystrophy. In fact, woman met man when she was taking her dad to the MS clinic. Both of their parents did not suffer from MS.





1. Draw a pedigree showing two generations – man, woman and their respective parents. Use the correct symbols for your pedigree, and fill in the genotypes for those individuals that you can determine. You don't have to draw this.. just wanna know how to.... draw..


2. Draw a punnett square to determine the possible outcomes for their children, with respect to Duchenne muscular dystrophy.


3. What is the percentage chance that any of their children will suffer from this disease?


4. What is the percentage chance that they will have a girl who does not have the disease?

I got question about sex-linked genes?
it will be a boy to have it becuase girls is xy and it is carried on the x alle in which the boys have 2 x alles.


boys have a 50 percent chance of having it.





they will have a 75 percent chance they they will have a girl that doesnt have it.
Reply:Ok, this is a disease linked to the "X" chromosome. So, males, who have an XY can get the disease if their mother is carrying the disease. Women can only get the disease if both of her parents have the disease as well. So, 25% of their children will have the disease. 50% will be carriers and the remaining 25% will not carry it at all. I hope that helps you answer your questions.
Reply:Ok as pointed out this is a SEX_LINKED condition, meaning its carried on the SEX chromosomes eg X or Y. In this case its on the X ( think of a Y as an X with an arm broken off....in the "missing arm" there is mostly nothing, but a few genes are carried on it...the result is that a Y chromosome does not have any corresponding genes.....I'll discuss more later)





Firstly look the genotpyes and phenotypes so you can figure out what your parents genotypes are:


D= normal and d=duchenne MD


XDXD= normal female


XDXd= Carrier female


XdXd= affected female





XDY = normal male


XdY= affected male....you can see that females can be carriers for this condition...in that they will not get it but pass it on. MALES cannot pass this condition to their SONS....as they pass on the Y chromosome, but can pass to their daughers and mothers can pass on to both sons and daughers.





So an affected man ( XdY) and a womans whos father had it XDXd ( means she must be a carrier as her father has a defective X chromosome which he passes onto all daughters).





In a pedigree charts males are square and females are circles. normal conditions are empty shapes, affected are fully coloured and carriers are half coloured.


The affected man ( will be a coloured square) will have a carrier mother ( XDXd shown as a half circle) and normal father ( XDY or empty square)


His partner will be a half circle to show she is a carrier. Her father will be normal ( it says no parent had the condition) and her mother will also be a carrier ( half circle).





2. THe cross will be XdY x XDXd


--------XD---------Xd


Xd----XDXd-----XdXd...50% of females affected, 50%carriers


Y-------XDY-------XdY--50% males affected 50% normal





3. the chance that ANY child ( irrespective of sex) will be 50% chance being affected.


4. a chance that a girl will not be affected is 50%.