Free Practice Quiz Question List

4 Sequence Alignment Online Quiz Questions

Use this free practice quiz with 20 questions to review 4 Sequence Alignment, test your knowledge, and prepare for your next test or exam.

20 questions

Choose one

1 point

When aligning protein sequences, what is the main reason to use a substitution matrix such as BLOSUM rather than treating every amino-acid mismatch identically?

A
They identify the exact evolutionary event that created each gap.
B
They score amino-acid replacements according to how compatible they are.
C
They guarantee that all sequences are evolutionarily related.
D
They measure the query coverage of a database search.

True or false

1 point

If a column is highly conserved across several aligned sequences, that observation alone establishes the specific function of the residue in that column.

A
True
B
False

Written response

1 point

What classic method finds an optimal local alignment under a chosen scoring scheme?

Fill in the blank

1 point

An MSA evaluation that adds scores for residue pairs across alignment columns can use a score.

Choose one

1 point

Two long sequences are mostly unrelated, but you suspect they share one domain. Which alignment approach best addresses this question?

A
Use global alignment because it forces every residue to match.
B
Use multiple sequence alignment because the sequences have different lengths.
C
Use local alignment to find the shared region while leaving unrelated flanks unaligned.
D
Use a substitution matrix to remove unrelated flanking regions automatically.

True or false

1 point

A gap in an alignment, by itself, identifies exactly when and in which ancestral sequence an insertion or deletion occurred.

A
True
B
False

Written response

1 point

What statistic estimates how many alignments with a score at least as good as the observed one would be expected by chance in a search of that size?

Choose all

1 point

Which statements accurately describe common progressive strategies for multiple sequence alignment? Select all that apply.

A
They commonly estimate similarities and build a guide tree before adding sequences progressively.
B
An early alignment error can affect later steps.
C
They guarantee identical alignments across tools and settings.
D
Different tools or settings may yield different results, particularly for highly divergent sequences.

Fill in the blank

1 point

In an affine gap-cost model, the penalty is larger for than for extending an existing gap.

Choose all

1 point

A database search returns a high-scoring local alignment. Which actions are appropriate before concluding that the match is biologically meaningful? Select all that apply.

A
Inspect the E-value as evidence about chance matches in a search of that size.
B
Treat the high score as conclusive proof of common ancestry.
C
Check alignment length and query coverage.
D
Consider biological context and independent evidence where available.

Choose one

1 point

Two sequences are similar in length and are expected to correspond from end to end. Which approach best fits this comparison?

A
Local alignment, because it excludes all gaps.
B
Global alignment, because the sequences are expected to correspond across their full lengths.
C
Multiple sequence alignment, because it compares exactly two sequences.
D
A consensus sequence, because it forces end-to-end correspondence.

Open ended

1 point

Why is a high-scoring multiple sequence alignment not automatically biologically correct? Give one reason and one way to assess or validate the proposed positional correspondence.

True or false

1 point

Identity counts exactly matching residues, whereas similarity may also count conservative amino-acid replacements according to a defined convention.

A
True
B
False

Choose one

1 point

What does it mean to say an alignment is optimal under a specified scoring scheme?

A
It proves that every aligned residue shares the same evolutionary history.
B
It is necessarily the biologically correct alignment regardless of parameter choices.
C
It has the best score under the specified scoring model, though different scoring choices may favor another alignment.
D
It establishes that the sequences are homologous even if the match is short or low-complexity.

Choose one

1 point

Two long protein sequences are not expected to correspond end to end, but may share one domain. Which alignment approach best fits this goal?

A
Use a global alignment because it finds the best-matching subsections and leaves unrelated flanks unaligned.
B
Use a local alignment because it can identify a shared domain while leaving unrelated flanking regions unaligned.
C
Use a multiple sequence alignment because it compares only two sequences at a time.
D
Use a global alignment because it ignores gaps in regions that do not match.

Choose one

1 point

A researcher wants to identify a conserved pattern across a protein family of five sequences. Which approach directly aligns the group in shared columns?

A
It aligns two sequences across their full lengths.
B
It aligns two sequences only within their best-matching subsections.
C
It aligns three or more sequences in shared columns.
D
It compares sequence scores without arranging residues into columns.

Choose one

1 point

An alignment report counts some conservative amino-acid replacements as similar, even when the residues differ. Which interpretation is correct?

A
Identity requires exact residue matches, while similarity may also count conservative replacements.
B
Similarity requires exact residue matches, while identity may count chemically similar replacements.
C
Identity and similarity both count only exact residue matches.
D
Identity counts gaps as matches, while similarity excludes gaps.

Choose one

1 point

When selecting a protein substitution matrix, which statement correctly describes BLOSUM matrices?

A
They are derived from DNA matches and do not affect which amino-acid similarities are favored.
B
They are derived from gap lengths and determine only how strongly gaps are penalized.
C
They are derived from conserved protein sequence blocks and influence which amino-acid replacements are favored.
D
They are derived from alignment coverage and estimate how many matches occur by chance.

Written response

1 point

An affine gap cost is calculated as $\text{gap cost}(k)=-(a+bk)$ . If $a=3$ , $b=1$ , and $k=4$ , what is the gap cost? Enter the result as a number.

Written response

1 point

What specific relationship does a sequence alignment model between residues placed in corresponding columns? Enter the concise two-word concept.