During the last two decades, use of the techniques of molecular biology (including recombinant DNA technology) in genetic studies gave several surprises. Some of these surprises led to the discovery of the following : (i) split genes,
meaning that the sequences containing actual information of the gene (exons
) are interrupted by other sequences (introns)
which are spliced out after transcription; (ii) overlapping genes,
meaning that same DNA sequences can become part of two or more genes expressed at different times and in different reading frames (consult The Genetic Code
, for reading frames); and (iii) pseudogenes,
which represent DNA sequences derived from mRNA through reverse transcription; these pseudogenes, therefore, differ from the split genes to which they belong, due to the absence of intron sequences. These interesting and surprising developments in the study of genetics will be discussed in this section, although for a full appreciation of this discussion, the readers may need to study some of the other further topics. However, a knowledge of these features of genes is partly also necessary for understanding the concepts discussed in later topics of genetics on Biocyclopedia.com.