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Deletion Mapping: Closing the
gap
Chromosome aberrations provide
shortcuts to mapping
 Deletions are particularly useful
 Principle: a deletion heterozygote
with a single copy of the mutant
allele should express the
phenotype if the gene maps within
the deletion complex

Deletion mapping the Y
chromosome
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Identify males with cytologically
aberrant Y chromosomes
Test each male for presence or absence
of sequence known to map to the Y
chromosome
Order the results into a conservative
map (the deletion map)
Inserting SRY into the deletion
map of the Y chromosome

Test individuals with “odd” sex:
– XY females (lack SRY and define portion of
Y not required for sex determination)
– XX males (have acquired SRY and define
portion of Y essential for sex determination)
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
Screen libraries to conduct “chromosome
walking” from known sequences
Test retrieved candidate sequences for
biological criteria
Two important questions in
gene cloning

How do you get there?
– SRY: deletion mapping and chromosome
walking

How do you know you are there?
– SRY: evolutionary conservation in males
(“Noah’s ark” blots), interesting sequence,
function proven by transgenesis (mouse
Sry gene in XX will cause sex reversal to
male)
DMD: Another monument to
deletion cloning
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Duchenne’s muscular dystrophy known
to be X-linked
Regional mapping accomplished by two
chromosome aberrations:
– deletion of DMD and several other
genes
– Translocation interrupting the DMD
gene