BioinformaticsLesson 2 of 2 in the course Genomics and sequencing

Sequence Assembly: Methods, Technologies, and Quality Assessment

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Sequence assembly reconstructs a longer DNA or RNA sequence from shorter sequencing reads. Because sequencing technologies generally read only fragments at a time, assembly is an essential step in turning raw sequencing data into a useful sequence.

A sequencing instrument may produce reads ranging from a few dozen to many thousands of bases, depending on the technology. These reads are fragments of a larger DNA sequence or, in some cases, of transcribed RNA. An assembler identifies overlaps and relationships among the reads and combines them to reconstruct longer sequences.

All flashcards

What is hybrid assembly?
Combining reads from different sequencing technologies to use their complementary properties, such as accuracy and read length.
What does the Overlap/Layout/Consensus (OLC) approach do?
It identifies overlaps between reads, arranges the reads into a layout, and derives a consensus sequence.
What does a de Bruijn graph represent in assembly?
Relationships among short sequence words called k-mers.
How does EST assembly differ from whole-genome assembly?
EST assembly uses fragments derived from transcribed mRNA rather than reads representing the whole genome.
What does BUSCO assess in a genome assembly?
Gene-content completeness by checking for expected single-copy orthologs in a chosen group.

Quiz questions

  1. Why can a greedy assembly method fail to produce the best overall assembly?Answer: A locally highest-scoring choice may not lead to the globally best result.
  2. How can long reads help resolve repeated regions during assembly?Answer: They can span repeats and connect them to neighboring sequences.
  3. What is a key purpose of hybrid assembly?Answer: To combine complementary read properties from different technologies.
  4. Which tool assesses assembly gene-content completeness by checking expected single-copy orthologs?Answer: BUSCO
  5. Why can EST read coverage vary greatly among genes?Answer: Transcript abundance varies, so highly expressed genes can produce many reads.

Based on the Wikipedia article Sequence assembly, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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