Question

4. What is a segmental duplication? Are they common in natural populations? Give two examples, not found in your textbook, of how they could affect a person’s phenotype.

Answer 1

Answer:

• Segmental Duplication: Long DNA sequences (generally more than 1kb in length) which consists nearly identical nucleotide sequences (sequence similarity near to 90-100%) caused due to duplication event and located in multiple sites of chromosome or chromosomes are called segmental duplication (SD).
• These regions are also called Low Copy repeats or LCR.
• These sequences are some time very large in size similar in sequence that causes chromosomal instability. There are mainly two types of SDs.
• When sequence are duplicated onto non-homologous chromosomes called Interchromosomal Segmental Duplication, and when sequence are duplicated on the same chromosome called Intrachromosomal Segmental Duplication.
• They are very common in natural population.
• According to genome analysis approximately 5% of the human genome is composed of duplicated sequence.

Effects of Segmental Duplication on phenotype:

• In case of duplication some time s it was found that after duplication one of the duplicate gene retains the original function whereas the other one evolves a new gene function.
• New function may be beneficial may be detrimental.
• This process is called neofunctionalization.
• Presence of large and highly homologous DNA sequences enhances the chances of gene rearrangement by nonallelic homologous recombination which may cause in deletion, duplication, or inversion of the intervening sequence.
• Another process is called Subfunctionalization where both the duplicated genes are mutated but they evolve to complement each other and restore the function of wild type gene.

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