linkage rather than a limited number of related individuals in a family. The results are expressed in probability terms that an individual with the linked STR allele is likely to have the disease gene.
Sibling studies are the third approach to linkage studies. Monozygotic (identical) and dizygotic (fraternal) twins provide convenient genetic controls for genetic and environmental studies. Monozygotic twins will always have the same genetic alleles, including disease genes. There should be 100% recurrence risk (likelihood) that if one twin has a genetic disease, the other twin has it, and both should have the same linked STR alleles. Fraternal twins have the same likelihood of sharing a gene allele as any sibling pair. Investigation of adoptive families may also distinguish genetic from environmental or somatic effects.
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