82 Chapter 3 • The Chromosomal Basis of Inheritance independently. These cases showed inheritance patterns that suggested that some combinations of genes were in-herited together, in other words as though they were on the same chromosome (see Chapter 4). Also, the thou-sands of characteristics of an organism seemed to require thousands of genes. So, well before the advent of DNA sequencing techniques, it was clear that a chromosome represents large numbers of genes in a speciFc linear ar-ray, and that this array is different for different chromo-somes. Molecular techniques available before the advent of large-scale sequencing also supported this general principle. Genomic sequencing did however show the details that were previously lacking. In particular, sequencing identiFed features of the DNA between genes, not only the sizes of intergenic segments, but also the presence there of repeating segments. Sequencing also showed that genes vary enormously in size, both between and within species. Most of this variation is caused by differ-
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