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how would a change to the sequence of nucleotides in a dna segment affect the mrna transcribed from the dna?

A change in the nucleotide sequence of a DNA segment will usually produce a complementary change in the sequence of the mRNA transcribed from that DNA, because mRNA bases are added by base‑pairing to the template strand of DNA during transcription.

Quick Scoop: What Actually Changes?

When a cell transcribes DNA to mRNA, an enzyme reads one DNA strand and builds mRNA using base‑pair rules (A–U and C–G). So if the DNA sequence is altered (a mutation), the enzyme simply copies that new sequence into mRNA, base by base.

In simple terms:

  • Change the DNA letters → you change the mRNA letters at the matching positions.
  • No change in DNA → no change in that part of the mRNA (for that gene and that cell).

Types of Effects on mRNA (and Beyond)

What happens depends on how the DNA sequence changes:

  1. Substitution (one base swapped)
    • One DNA base is changed, so one mRNA base changes at that position.
 * This changes one codon (a 3‑base “word”) in the mRNA, which may or may not change the amino acid in the protein.
  1. Insertion or deletion (bases added or removed)
    • Extra DNA bases or missing bases shift how triplets are read, so many downstream mRNA codons change.
 * The mRNA sequence after the mutation can be very different, often leading to a very altered or shortened protein.
  1. Change in non‑coding / regulatory regions
    • If the change is in a promoter or regulatory DNA, it might affect how much mRNA is made (more, less, or none) rather than its sequence.
 * The actual coding part of mRNA could stay the same, but its **amount** in the cell changes.

One Concrete Example

Imagine a short DNA template segment:

  • Original DNA (template): 3′–TAC GAA–5′
  • Original mRNA: 5′–AUG CUU–3′ (two codons).

If the DNA mutates:

  • DNA change: 3′–TTC GAA–5′
  • New mRNA: 5′–AAG CUU–3′

Only the first mRNA codon changed, because only that part of the DNA sequence was altered.

Bottom Line (TL;DR)

  • Transcription makes mRNA that is complementary to the DNA template, base by base.
  • So any change in the DNA nucleotide sequence in the transcribed region will usually cause a corresponding change in the mRNA sequence at those positions, and sometimes also affect how much mRNA is produced.

Information gathered from public forums or data available on the internet and portrayed here.