<em>Here is my intro to genetics...if you are interested read on, if not it may work as a sleep inducer <img src="i/expressions/face-icon-small-smile.gif" border="0"></em>
Hi, you might find it interesting to learn a little about "Simple Mendelian Genetics". This is the way genes are passed from each parent to the off-spring and is responsible for many, many characteristics, such as eye colour, height and certain diseases such as haemophilia and cystic fibrosis.
If you imagine you have 46 chromosomes in <em>every cell</em> of your body; these are little strings containing allyour genetic information. Each cell contains the genetic info for everything in your body. So the cells in your kidneys have the genes for eye colour, but those genes are switched off. The strings join up into pairs making 23 "chromosome pairs".
In the <em>sex cells</em> you only have 23 of these strings. So, when a sperm and egg cell fuse you get back to the number 46 in the embryo, and these cells divide and divide into cells each containing 46 chromosome strings.In this way a brand newindividual is created when a sperm and egg cell fuse.
There is a certain chromosome pair in every cell (pair number 7 I think) and on each of the chromosome strings there is a gene responsible for trafficking sodium chloride (salt) from inside the cell to the outside. One gene is on the string passed from the father and one gene is on the string passed from the mother.In a person with CF, there is a fault or mutation in this gene <strong>on each string</strong>. If the fault is only onthe gene of one string then the person is a carrierand does not have CF.There are over 1800 ways the gene can be mutated or faulty. The fault called DF508 is the most common. The genes on each string can be the same (homozygous) or different (heterozygous). There are different schools of thought relating to whether or not the type of gene (genotype) affects the health outcome of the person (phenotype).
Note that in a carrier (someone with the faulty gene only on one string in pair number 7), their sex cells will be split 50:50 into strings carrying a faulty gene and strings carrying a working gene. When they procreate with a non-carrier, there is a 1-in-4 chance of passing on the faulty gene, in which case1 in 4 childrenwill also be carriers. That couple will not produce a child with CF. If the carrier procreates with another carrier, there is a 1-in-4 chance of the child having CF, 1-in-4 chance of being a carrier and 1-in-2 chance of having nothing at all, meaning two working genes.
To answer your question- when the docs talk about the "two genes", this is not surprising, it is the very reason your daughter has CF and it says nothing about how severe/ mild her outcome will be.Personally I find this fascinating and I would recommend you look into it, but that is just a personal preference.
I am adding a link below to a youtube video on Mendelian genetics, I find it interesting...maybe that's the nerd in me <img src="i/expressions/face-icon-small-smile.gif" border="0">
<a href="http://www.youtube.com/watch?v=NWqgZUnJdAY">http://www.youtube.com/watch?v=NWqgZUnJdAY</a>