Restriction Digest Result
Allele 1 contains 3 repeat units, 250 bp restriction product Allele 2 contains 6 repeat units, 400 bp restriction product
Fig. 4. Schematic diagram describing length polymorphisms of a VNTR sequence. Allele 1 contains three VNTR repeats (open boxes), whereas allele 2 only contains six repeats. These result in different size fragments, 250 bp or 400 bp, being detected by gel electrophoresis.
of approx 1 per 10 kb of sequence (12,13). Polymorphic DNA sequences can be used as markers for determining allelic inheritance of disease-causing genes and for identity testing.
Mutations represent permanent alterations to a DNA sequence. Common mutations, although representing sequence variants, are not usually considered polymorphisms, by virtue of the fact that they represent a rare genetic event (occurring with a frequency of less than 0.1%). Two general categories of point mutations include transitions and transversions. These mutations involve specific substitutions of the organic bases that make up a DNA sequence. The bases adenine and guanine are purine bases, whereas thymine and cytosine are pyrimidine bases. A transition mutation involves a substitution of a purine with another purine, or a pyrimidine with another pyrimidine; a transversion mutation involves the substitution of a purine for a pyrimidine or vice versa. The clinical significance of a mutation is determined by the type of mutation; its location within the gene; and the tissue involved, as not all tissues express all genes. Germline mutations are those that occur in germ cells— cells that give rise to gametes—and are, thus, heritable; these mutations will be present in every cell of the body in subsequent generations. In contrast, an acquired mutation by a cell other than a germ cell is referred to as a somatic mutation. These mutations are only passed on to daughter cells within an individual and are not heritable.
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A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.