Question:
How can most of our population be recessive for diseases?
Replies:
You need to understand what recessive really means. Remember that our DNA
codes for proteins and proteins are what makes up most of our structure. Its
also makes up enzymes and hormones that control the way our bodies work. So
lets say that you have a gene that codes for a structural protein. The
"dominant" form is the instruction for the normal version of the protein.
The "recessive" form may be a faulty version of the instruction and either it
makes a protein that doesn't work AS WELL or it is so messed up that it
doesn't code for the protein at all. Sometimes if you have one good version
of the gene and one faulty version , ie you are heterozygous, one copy of the
good gene makes enough of the protein to get you by. Some people who are
heterozygous get only half of the protein, and the structure that is coded
for is only half as strong.
If you have two bad versions (you are homozygous
recessive) you don't make any of the protein. This may affect your survival
if it is a really important protein. Most of us DO carry instructions for
making all of our proteins, so most disorders are recessive. However some
disease genes come in the dominant form such as Huntington's disease, where
having too MUCH of a certain protein can be harmful.
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