Inherited Defects
INTRODUCTION
Genetic defects vary from
trivial to life threatening. Although we tend to think of inherited conditions
such as diabetes and muscular dystrophy as diseases, we often refer to cleft
palates or color blindness as inherited defects. However, they are all the
result of mutations in DNA, the genetic material. Not only are some diseases
directly caused by mutations, but susceptibility to infectious disease and
other damaging environmental factors, such as radiation, is also influenced by
a variety of genes.
Precise rates of mutation are
difficult to estimate, but for humans and apes, the mutation rate is around 5.0
× 10-8 per kilobase of DNA per generation. For
rodents, the rate is some 10-fold less because fewer cell divisions are needed
to form gametes from ancestral germ cells. Thus a considerable number of
mutations are constantly accumulating in the germline of humans and other
animals. Most of these have little or no effect, but a small percentage give
rise to serious hereditary defects. A full listing of human hereditary defects,
known as OMIM (Online Mendelian Inheritance in Man), is available on the
Internet at http://www.ncbi.nlm.nih.gov/ entrez/query.fcgi?db=OMIM.
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