Biology Reference
In-Depth Information
FIGURE 3.3. Diagrammatic representation of homozygosity for the disease allele
(D) and flanking markers to a disease locus in the offspring of a first cousin union
in autozygosity mapping.
1995). This approach has been utilized to identify the majority of the loci
for autosomal recessive nonsyndromic sensorineural hearing impairment,
e.g., mapping of the first locus for autosomal recessive nonsyndromic sen-
sorineural hearing impairment,
DFNB1
(Guilford et al. 1994; Brown et al.
1996).
4. Genome Searches
In most instances, there are no clues to the chromosomal location of a gene,
and genetic mapping involves the “shotgun” approach of a total genome
search. This involves analyzing DNA samples from family members for a
standard battery of approximately 300 polymorphic DNA markers evenly
spread throughout the human genome. Until recently, this approach was
fairly time-consuming and laborious. The advent of semi-automated
computer-driven gel analysis of fluorescently labelled microsatellite
markers means that, if the necessary number of samples from the families
have been collected and the reaction conditions for the marker set are opti-
mized, a genome search can be carried out in a matter of weeks, rather than
years.
