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Figure 11.3 The exon/intron structure of the D. melanogaster period gene. The gene is 7 kb long,
with seven exons. The location of the per L , per 0 , and per S mutations are indicated, as is the region
which codes for the variable number (17, 20, or 23) of Thry/Gly repeats.
functions common to all (clock-type functions), whereas species-specific dif-
ferences, such as love songs, locomotor activity, and eclosion profiles, may be
encoded within the variable regions ( Kyriacou 1990 ).
Clock + , timeless + , cycle + , and doubletime + are components of the circadian
clock ( Kyriacou 1993 , Table 11.2 ). In addition, autosomal mutations induce flies
to eclose early in a light-dark cycle; flies with mutations of phase-angle + emerge
in the pre-dawn part of the cycle instead of just after dawn, while flies with
mutations of gate + fail to eclose during this narrow time window.
The cryptochrome + ( cry + ) gene is an important clock gene because it encodes
a critical circadian photoreceptor in Drosophila ( Egan et  al. 1999, Emery et  al.
2000 ). The gene product CRY belongs to a family of blue light-sensitive proteins
that includes photolyases and plant blue-light photoreceptors. Flies overexpress-
ing CRY are hypersensitive to light. The CRY protein is probably the only dedi-
cated circadian photoreceptor in Drosophila ( Emery et al. 2000 ).
11.5.1.2 Song-Cycle Behavior in Transgenic Drosophila
The courtship song is produced when D. melanogaster males vibrate their
wings. The song consists of two components: 1) courtship hums, and 2) a series
of pulses with interpulse intervals that can fluctuate between 15 and 85 millisec-
onds (ms) ( Kyriacou and Hall 1989 ). The variation in interpulse intervals ranges
from a period of 56ms in D. melanogaster and 35-40ms in D. simulans . The
males of D. melanogaster with the per S mutation sing with 40-ms periods,
per L males sing with 76-ms periods, and per 0 males are arrhythmic.
The genetic basis of species-specific song instructions was confirmed by the
transfer of the per + gene cloned from D. simulans into D. melanogaster via
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