Question

The average length of 1 cM in humans is 1,000,000 base pairs. However, in some regions of the human genome, 1 cM is closer to 100,000 base pairs. What types of sequences can you infer that are in these particular regions? What evidence supports your answer?

Answer 1

Each DNA molecule contains many genes, which are its functional units. These genes are arranged in a defined order along the DNA molecule. Most genes code for protein molecules—enzymes or structural elements—that determine the characteristics of a cell.

In eukaryotes the coding segments in a gene (called exons) are generally separated from one another by noncoding segments (called introns).

So the difference is due to presence of sequences called introns.

Often each exon will encode a different structural region (or domain) of a larger protein molecule. Many exons have been found to be part of a family of related coding sequences that are used in the construction of many different genes Because of the many introns in mammalian genes, a single gene is often more than than 10,000 nucleotides long, and genes that span 100,000 nucleotides are not uncommon

For the information in the coding sequences of a gene to be expressed, the DNA of a gene must first be transcribed into an RNA molecule.

Evidence is supported by the process of RNA splicing

Before RNA strand leaves the cell's nucleus, the intron sequences are cut out of this RNA strand by a process called RNA splicing, thereby bringing the exon sequences into contiguity. Then the RNA can be translated into a protein molecule according to the genetic code.

Some other sequences that can be the reason for this paradox are:

• Regulatory elements of genes
• Pseudogenes
• Multiple copies of genes
• Intergenic sequences
• Repetitive DNA

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