D1.3.10 (HL)—Conserved sequences
Conserved sequences remain similar across species because important functions can be maintained by purifying selection over evolutionary time in lineages.
- Syllabus
- First assessment 2025
- Objective
- D1.3.10
- Level
- HL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceNovember 2018
Most common paperPaper3
Typical marks1
Common command terms
- Identify
Recent exam appearances
November 2018Paper3 ["HL"] · TZ011(d)[ 1 ]D1.3.10 (HL)—Conserved sequences
Practice this objective
Coverage 2018–2018 · Updated 16 Jul 2026
Conserved Sequences Reveal Important Functions
HL onlyConserved gene sequences remain identical or similar across species; highly conserved sequences remain similar across long evolutionary periods.
| Hypothesis | Why similarity persists |
|---|---|
| Functional requirement | Many sequence changes reduce the gene product's function, so purifying selection removes them |
| Slower mutation rate | The sequence accumulates new mutations less often than less-conserved regions |
If the same coding region is very similar in distantly related species, researchers can hypothesize that its amino-acid sequence is strongly constrained by the protein's function.
Conservation supports hypotheses; it does not by itself identify the exact function or distinguish functional constraint from a lower mutation rate. Further evidence is required.
Conserved sequences
HL onlyAssessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, commonly using Identify.
Command terms
Identify
What earns marks
Build the answer around this relationship: Conserved sequences are similar across species or long evolutionary times.
Representative question
Question 1
A bioinformatics analysis was performed on the protein PSY transcribed from the gene from corn and from daffodil to obtain the sequence alignment.
On the alignment, identify the longest part of the sequence where the consecutive amino acids are the same.
| Corn | ---MAI I LVRAASP-------GLSAAD---------SISH- |
|---|---|
| Daffodil | ---MVVAILRVVSAIEIPIRLGFSEANWRFSSPKYDNLGRK |
| Corn | QGTLQCSTLLKTKRPAARRWMPCSLLGLHPWEAGRP-SPAV |
| Daffodil | KSRLSVYSLYTTSKYA-----------CVGFEAENNGKFLI |
| * * * * * * | |
| Corn | YSSLPVNPAGEAVVSSEQKVYDVVLKQAALLKRQLRTP--V |
| Daffodil | RSSLVANPAGEATISSEQKVYDVVLKQAALVKDQTKSSRKS |
| * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | LDARPQDMDMPRN--GLKEAYDRCGE I CEEYAKTFYLGTML |
| Daffodil | TDVKP-DIVLPGTVYLLKDAYDRCGEVCAEYAKTFYLGTLL |
| * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | MTEERRRA I WA I YVWCRRTDELVDGPNANY I TPTALDRWEK |
| Daffodil | MTPERRRAI WA I YVWCRRTDELVDGHNASHITPSALDRWEA |
| ** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | RLEDLFTGRPYDMLDAALSDTISRFPIDIQPFRDMIEGMRS |
| Daffodil | RLEDLFAGRPYDMFDAALSDTVSRFPVDIQPFMDMVEGMRM |
| * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | DLRKTRYNNFDELYMYCYYVAGTVGLMSVPVMGIATESKAT |
| Daffodil | DLKKSRYKNFDELYLYCYYVAGTVGLMSVPVMGIAPESLAE |
| * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | TESVYSAALALGIANQLTNI LRDVGEDARRGRIYLPQDELA |
| Daffodil | AESVYNAALALGIANQLTNI LRDVGEDARRGRIYLPQDELA |
| * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | QAGLSDEDIFKGVVTNRWRNFMKRQIKRARMFFEEAERGVN |
| Daffodil | EAGLSDEDVFTGKVTDKWRSFMKRQIKRARTFFEQAEKGVT |
| * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * | |
| Corn | ELSQASRWPVWASLLLYRQI LDEIEANDYNNFTKRAYVGKG |
| Daffodil | E L SQA SRWP VWASLL LYRQI LDE I EANDYNNF TKRAYVSKV |
| Corn | KKLLALPVAYGKSLLLPCSLRN---GQT |
| Daffodil | KRLAALPLA YGKSLLIPLSLRPPSLSKA |
| * * * * * * * * * * * * * * * * |
HL Gene Editing Evidence
HL onlyGene knockout makes a specific gene non-functional to investigate phenotype; model organisms such as mice, Drosophila, zebrafish, and Arabidopsis support KO libraries. Guide RNA directs Cas9 to a complementary DNA target sequence; Cas9 cutting enables deletion, replacement, insertion, or gene disruption. Conserved sequences remain similar across species or long evolutionary times; conservation suggests essential function, lower mutation rate, or strong purifying selection.
Concept essentials
- Conserved sequences are similar across species or long evolutionary times.
- Alignment can reveal identical or highly similar sequence regions.
- Strong conservation often suggests functional importance.
- Purifying selection can maintain essential sequences by removing harmful changes.