Introduction 
CO 
CD 
41 
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O LJ-J 
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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., and Kidd, K.K. The Human 
Genome Map. Science 250: October 12, 1990. Copy- 
right 1990 by the AAAS. 
EXON INTRON 
(CODING (NONCODING 
REGION) REGION) 
HNAi 
CAl' 
I'RIMARY 
niRNA 
transc:rii>i 
■ ^1 3 1 4 1 5 M m 
I RANSC RII'TION 
I'OLY A 
■ ■ in MM 
IN IKONS ARE CUl OU 1 AND 
CODINC; RECKONS ARE 
SI'LICED TOGETHER 
MATURE niRNA TRANSCRIPT |(] 
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 76:2255-2257. 
