1. ©2000 Timothy G. Standish John 15:4 4Abide 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

2. ©2000 Timothy G. Standish From Sequence to Chromosome: The Tip of the X Chromosome of D. Melanogaster Timothy G. Standish, Ph. D.

3. ©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

4. ©2000 Timothy G. Standish Telomere Chromosome Morphology Arm Stained polytene chromosomes exhibit distinctive banding patterns Centromere Proximal Distal Proximal Distal

5. ©2000 Timothy G. Standish Telomere Chromosome Morphology Arm Centromere During development chromosome puffs appear which are thought to be correlated with transcriptional activity

6. ©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

7. ©2000 Timothy G. Standish Drosophila X Chromosome 2b Figure from http://www.helsinki.fi/~saura/EM/xdiv2.html In division 2b of the X chromosome, a strange bulge appears in images of polytene chromosomes In situ hybridization using cosmid clones mapped to that region show hybridization on the outside of this structure, but not in the middle

8. ©2000 Timothy G. Standish Cosmids A cosmid is a plasmid with the phage cos site included in it The cos site signals for packaging into phage, thus the plasmid, including a large insert can be packaged into phage particles without having to waste space on genes A cosmid combined with a cloned insert cannot exceed the 53 kb limit on how much can be packaged into the phage head

9. ©2000 Timothy G. Standish An Inverted Repeat May Account For Strange Morphology At X2B 350 bp 3.5 repeats of satellite-like element l These repeated elements resemble the 1.688 satellite found in units of 1 - 4 on the X chromosome l Results indicate that inverted repeats can influence chromosome architecture even when separated by significant distances

10. ©2000 Timothy G. Standish