Two sisters. One diagnosed with cystic fibrosis, one was not?!
Question: Two sisters!. One diagnosed with cystic fibrosis, one was not!?
I had a friend growing up!. She had cystic fibrosis!. She died when she was 22 of the disease!. Her younger sister did not inherit the disease!. How does this happen that only one has it if both parents are carriers!?Www@Answer-Health@Com
Answers:
I am a younger surviving sister without CF who had an older sister who died from CF when she was 33!. Basically if both parents are carriers they have a 1 in 4 chance of having a child with CF!. While my sister had CF, neither my brother nor I did!. However, I have been tested and I do carry the CF gene which means that if I partner someone who also carries the gene then again we have a 1 in 4 chance of having a child with CF!. The sister you mention who did not have CF should be tested to see if she is a carrier, as should anyone in the immediate family!. If she is then this will not affect her health at all, but she should be aware that any man she may have a child with must be tested too in order to evaluate the risk of her having a child with CF!. I hope that helps!.
The 1 in 4 chance works like this:
Being a CF carrier means:
Mother has 1 bad chromosone and 1 good
Father has 1 bad chromosone and 1 good
when they have a child they can pass either:
Mother & Father pass both bad chromones = CF child
Mother passes one bad and Father passes one good = No CF
Mother passes one good and Father passes one bad = No CF
Mother & Father pass both good = No CF
Hope thats easy to follow and makes senseWww@Answer-Health@Com
The 1 in 4 chance works like this:
Being a CF carrier means:
Mother has 1 bad chromosone and 1 good
Father has 1 bad chromosone and 1 good
when they have a child they can pass either:
Mother & Father pass both bad chromones = CF child
Mother passes one bad and Father passes one good = No CF
Mother passes one good and Father passes one bad = No CF
Mother & Father pass both good = No CF
Hope thats easy to follow and makes senseWww@Answer-Health@Com
Chromosomes are paired but then split when the eggs and sperm are created so that when the sperm fertilizes the egg the resulting cell again has paired chromosomes!.
So you start with 46 chromosomes, a sex cell (egg or sperm) are created with 23 chromosomes then when the egg is fertilized it has 46 or 23 pairs!.
This is important since CF is a recessive gene and is not on both chromosomes!. So if you look for the recessive gene it is only on one chromosome but the child gets the disease when she/he gets 2 chromosomes with the recessive gene!.
So if you look at the parents they each have a chromosome!. One with the recessive gene and one without!. In this case one twin got 2 chromosomes with the recessive gene and the other either got 2 chromosomes without the recessive gene or one with and one without!. In any case the second sister does not get CF!.
Obviously these girls were Fraternal twins, ie: 2 fertilized eggs!. If they were identical twins they would both have CF since they would be genetically identical!.Www@Answer-Health@Com
So you start with 46 chromosomes, a sex cell (egg or sperm) are created with 23 chromosomes then when the egg is fertilized it has 46 or 23 pairs!.
This is important since CF is a recessive gene and is not on both chromosomes!. So if you look for the recessive gene it is only on one chromosome but the child gets the disease when she/he gets 2 chromosomes with the recessive gene!.
So if you look at the parents they each have a chromosome!. One with the recessive gene and one without!. In this case one twin got 2 chromosomes with the recessive gene and the other either got 2 chromosomes without the recessive gene or one with and one without!. In any case the second sister does not get CF!.
Obviously these girls were Fraternal twins, ie: 2 fertilized eggs!. If they were identical twins they would both have CF since they would be genetically identical!.Www@Answer-Health@Com