Transcript The Fly Genome

John 15:4
4
Abide in me, and I in you. As
the branch cannot bear fruit
of itself, except it abide in the
vine; no more can ye, except
ye abide in me
©2000 Timothy G. Standish
From Sequence to
Chromosome:
The Tip of the X Chromosome of
D. Melanogaster
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
The Drosophila Genome
180 million base pairs
120 Mbp has been sequenced
The sequenced portion is euchromatin thought to
be richer in gene sequences than the remaining
heterochromatin
Drosophila has a haploid number of 4: 3
autosomes plus 1 sex chromosome
Polytene chromosomes can be easily observed in
the salivary glands of larvae
©2000 Timothy G. Standish
Chromosome Morphology
Telomere
Distal
Arm
Proximal
Centromere
Proximal
Stained polytene
chromosomes
exhibit distinctive
banding patterns
Arm
Distal
Telomere
©2000 Timothy G. Standish
Chromosome Morphology
Telomere
Arm
Centromere
Arm
During development
chromosome puffs
appear which are
thought to be
correlated with
transcriptional
activity
Telomere
©2000 Timothy G. Standish
Naming Chromosome Parts
Chromosomes are numbered 1 - 3 X and Y
Each chromosome is divided into left (L) and
Right (R) arms
Arms are divided into numbered divisions going
left to right starting with the X chromosome distal
left arm and ending with division 100 on the distal
right arm of chromosome 3.
Divisions are divided into lettered subdivisions
going left to right
©2000 Timothy G. Standish
Drosophila X Chromosome 2b
In division 2b of the X
chromosome, a strange
bulge appears in images of
polytene chromosomes
Insitu hybridization using
cosmid clones mapped to
that region show
hybridization on the outside
of this structure, but not in
the middle
Figure from http://www.helsinki.fi/~saura/EM/xdiv2.html
©2000 Timothy G. Standish
Cosmids
A cosmid is a plasmid with the l page cos
site included in it
The cos site signals for packaging into l
phage, thus the plasmid, including a large
insert can be packaged into phage particles
without having to waste space on l genes
A cosmid combined with a cloned insert
cannot exceed the 53 kb limit on how much
can be packaged into the l phage head
©2000 Timothy G. Standish
An Inverted Repeat May Account
For Strange Morphology At X2B
3.5 repeats of
satellite like element
350 bp
l
l
These repeated elements resemble the
1.688 satellite found in units of 1 - 4 on
the X chromosome
Results indicate that inverted repeats can
influence chromosome architecture even
when separated by significant distances
©2000 Timothy G. Standish
©2000 Timothy G. Standish
©2000 Timothy G. Standish