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Introns are non-coding sequences of DNA that are present within genes in eukaryotic organisms. They are transcribed into pre-messenger RNA (pre-mRNA) molecules during transcription. However, introns do not contribute to the final protein products because they are removed from the pre-mRNA during the process of RNA splicing. The remaining sequences, called exons, are joined together to form the mature mRNA molecule, which is then used as a template for protein synthesis.

Yeast and humans have different intron frequencies. Yeast (Saccharomyces cerevisiae), being a simple single-celled eukaryote, has a relatively low intron frequency. Only about 4% of its genes contain introns, and most of these genes possess only a single intron. On the other hand, humans, as complex multicellular eukaryotes, have a much higher intron frequency. Approximately 90% of human protein-coding genes contain introns, and these genes often possess multiple introns. It has been estimated that the human genome contains around 190,000 introns.

There are significant differences in intron sizes between yeast and humans. In yeast, introns are relatively small, with an average size of around 250 base pairs (bp). In humans, introns vary in size and can range from less than 100 bp to hundreds of thousands of bp. The average intron size in the human genome is significantly larger than that in yeast, with some sources estimating it to be around 3,300 bp. The larger intron sizes in humans contribute to the overall larger size of the human genome compared to the yeast genome. In conclusion, intron frequencies and sizes differ considerably between yeast and humans, with yeast having a lower intron frequency and smaller introns, while humans have a higher intron frequency and larger introns. These differences reflect the varying degrees of complexity of the organisms and their genome organization.