Introduction 
X 
Figure 3- A schematic representation of the X chro- 
mosome showing the location of the characteristic 
banding patterns and the distribution of several of 
the genes that have been localized to this 
chromosome. 
Excerpt from Stephens, J.C., Mador, M.L., Cava- 
naugh, M.L., Gradie, M.I., andKidd, K.K. The Human 
Genome Map. Science 250: October 12, 1990. Copy- 
right 1990 by the AAAS. 
INTRON 
EXON INTKON 
(CODING (NONCODING 
REGION) REGION) 
, 1 , 
PNA- 
1 
■ 2B 3 ■ 4 ■ 5 
rUANSC:RII'TION 
CAP 
PRIMARY 
niRNAl 
TRANSt:HIIT 
I'OLY A 
INTRONS ARE CUT OUT AND 
COOING REGIONS ARE 
SI'LIGED HX;ETHtR 
MATURE inRNA TRANSCRIH 1 | fl TT 
Figure 4. The primary RNA transcript of a gene is very much larger than the message that is 
actually translated to form a protein. A variable number of noncoding sequences called introns 
are edited out, and the remaining exons are spliced together by a complex mechanism shown in 
the drawings to the left. 
From Dugaiczyk, A., Woo, S.L.C., Colbert, D.A., Lai, B.C., Mace, M.L., Jr., and O'Malley, B. 
1979. Proc Natl Acad Sci USA 76:2253-2257. 
OCOCOCl I % 
