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* polymorphism
 #153005  
  zkadhem - 01/16/07 03:19
 
  5. A polymorphism is best defined as
a. Cosegregation of alleles
b. One phenotype, multiple genotypes
c. Nonrandom allele association
d. One locus, multiple abnormal alleles
e. One locus, multiple normal alleles
 
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* Re:polymorphism
#619266
  zkadhem - 01/16/07 16:14
 
  5. The answer is e. Polymorphic loci have multiple alleles because of DNA sequence variation, including one or more with frequencies greater than 1%. This higher frequency and benign connotation differentiate polymorphic loci from those that harbor multiple disease-causing alleles. The DNA sequence changes may alter restriction sites [producing restriction fragment
length polymorphisms (RFLPs)], change the numbers of repeated segments [producing variable numbers of tandem repeats (VNTRs)], or alter the genetic code (producing variant proteins, or protein polymorphisms).Polymorphisms may cosegregate (be inherited together) with disease
alleles, allowing diagnosis by linkage analysis or estimates of risk through allele association (a.k.a. linkage disequilibrium, as with certain HLA alleles and diabetes mellitus). Different mutant alleles may cause indistinguishable phenotypes (allelic heterogeneity), as may mutations at different loci (genetic heterogeneity).
 
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