Phenethyl propionate

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Prediction done using the OECD QSAR toolbox version 3.3 with log kow as the primary descriptor and considering the five closest read across substances, gene mutation was predicted for 2-phenylethyl propanoate (122-70-3) .The study assumed the use of Salmonella typhimurium strains TA 1535, TA 1537, TA 98 TA100 and TA 102  with and without S9 metabolic activation system. 2-phenylethyl propanoate as predicted to not induce gene mutation in Salmonella typhimurium strains TA 1535, TA 1537, TA 98 , TA 100and TA102 in the presence and absence of S9 metabolic activation system and hence, according to the prediction made, it is not likely to classify as a gene mutant in vitro. Based on the predicted result it can be concluded that the substance is considered to not toxic as per the criteria mentioned in CLP regulation

Gene mutation toxicity was predicted for 2-phenylethyl propanoate (122-70-3) using the battery approach from Danish QSAR database (2017). The study assumed the use of Salmonella typhimurium bacteria in the Ames test. The end point for gene mutation has been modeled in the Danish QSAR using the three software systems Leadscope, CASE Ultra and SciQSAR. Based on predictions from these three systems, a fourth and overall battery prediction is made. The battery prediction is made using the so called Battery algorithm. With the battery approach it is in many cases possible to reduce “noise” from the individual model estimates and thereby improve accuracy and/or broaden the applicability domain.

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification

Justification for type of information:

Data is from OECD QSAR Toolbox version 3.3 and QMRF report has been attached.

Qualifier:

according to guideline

Guideline:

other: As mention below

Principles of method if other than guideline:

Prediction is done using QSAR Toolbox version 3.3.

GLP compliance:

not specified

Type of assay:

bacterial reverse mutation assay

Specific details on test material used for the study:

- Name of test material (IUPAC name): 2-phenylethyl propanoate
- Common name: Phenethyl propionate (PEP)
- Molecular formula: C11H14O2
- Molecular weight: 178.2296 g/mol
- Smiles notation: c1(CCOC(=O)CC)ccccc1
- InChl: 1S/C11H14O2/c1-2-11(12)13-9-8-10-6-4-3-5-7-10/h3-7H,2,8-9H2,1H3
- Substance type: Organic
- Physical state: Liquid

Target gene:

Histidine

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102

Details on mammalian cell type (if applicable):

Not applicable.

Additional strain / cell type characteristics:

not specified

Cytokinesis block (if used):

Not applicable.

Metabolic activation:

with

Metabolic activation system:

S9 metabolic activation

Test concentrations with justification for top dose:

No data available.

Vehicle / solvent:

Not specified.

Untreated negative controls:

not specified

Negative solvent / vehicle controls:

not specified

True negative controls:

not specified

Positive controls:

not specified

Details on test system and experimental conditions:

No data available.

Rationale for test conditions:

No data available.

Evaluation criteria:

Prediction was done considering a dose dependent increase in the number of revertants/plate

Statistics:

No data available.

Species / strain:

S. typhimurium, other: TA 1535, TA 1537, TA 98, TA 100 and TA 102

Metabolic activation:

with

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

not specified

Vehicle controls validity:

not specified

Untreated negative controls validity:

not specified

Positive controls validity:

not specified

Additional information on results:

Not specified.

The prediction was based on dataset comprised from the following descriptors: "Gene mutation"
Estimation method: Takes highest mode value from the 6 nearest neighbours
Domain  logical expression:Result: In Domain

(((((("a" or "b" or "c" or "d" or "e" )  and ("f" and ( not "g") )  )  and ("h" and ( not "i") )  )  and ("j" and ( not "k") )  )  and "l" )  and ("m" and "n" )  )

Domain logical expression index: "a"

Referential boundary: The target chemical should be classified as Esters (Acute toxicity) by US-EPA New Chemical Categories

Domain logical expression index: "b"

Referential boundary: The target chemical should be classified as Aryl AND Carboxylic acid ester by Organic Functional groups

Domain logical expression index: "c"

Referential boundary: The target chemical should be classified as Aryl AND Carboxylic acid ester by Organic Functional groups (nested)

Domain logical expression index: "d"

Referential boundary: The target chemical should be classified as Aliphatic Carbon [CH] AND Aliphatic Carbon [-CH2-] AND Aliphatic Carbon [-CH3] AND Aromatic Carbon [C] AND Carbonyl, aliphatic attach [-C(=O)-] AND Ester, aliphatic attach [-C(=O)O] AND Miscellaneous sulfide (=S) or oxide (=O) AND Olefinic carbon [=CH- or =C<] by Organic functional groups (US EPA)

Domain logical expression index: "e"

Referential boundary: The target chemical should be classified as Aromatic compound AND Carbonic acid derivative AND Carboxylic acid derivative AND Carboxylic acid ester by Organic functional groups, Norbert Haider (checkmol)

Domain logical expression index: "f"

Referential boundary: The target chemical should be classified as No alert found by DNA binding by OASIS v.1.3

Domain logical expression index: "g"

Referential boundary: The target chemical should be classified as AN2 OR AN2 >>  Michael-type addition, quinoid structures OR AN2 >>  Michael-type addition, quinoid structures >> Flavonoids OR AN2 >>  Michael-type addition, quinoid structures >> Quinones OR AN2 >> Carbamoylation after isocyanate formation OR AN2 >> Carbamoylation after isocyanate formation >> N-Hydroxylamines OR AN2 >> Michael-type addition on alpha, beta-unsaturated carbonyl compounds OR AN2 >> Michael-type addition on alpha, beta-unsaturated carbonyl compounds >> Four- and Five-Membered Lactones OR AN2 >> Schiff base formation OR AN2 >> Schiff base formation >> Polarized Haloalkene Derivatives OR AN2 >> Schiff base formation by aldehyde formed after metabolic activation OR AN2 >> Schiff base formation by aldehyde formed after metabolic activation >> Geminal Polyhaloalkane Derivatives OR AN2 >> Shiff base formation after aldehyde release OR AN2 >> Shiff base formation after aldehyde release >> Specific Acetate Esters OR AN2 >> Shiff base formation for aldehydes OR AN2 >> Shiff base formation for aldehydes >> Geminal Polyhaloalkane Derivatives OR AN2 >> Shiff base formation for aldehydes >> Haloalkane Derivatives with Labile Halogen OR AN2 >> Thioacylation via nucleophilic addition after cysteine-mediated thioketene formation OR AN2 >> Thioacylation via nucleophilic addition after cysteine-mediated thioketene formation >> Haloalkenes with Electron-Withdrawing Groups OR AN2 >> Thioacylation via nucleophilic addition after cysteine-mediated thioketene formation >> Polarized Haloalkene Derivatives OR Michael addition OR Michael addition >> Quinone type compounds OR Michael addition >> Quinone type compounds >> Quinone methides OR Non-covalent interaction OR Non-covalent interaction >> DNA intercalation OR Non-covalent interaction >> DNA intercalation >> Acridone, Thioxanthone, Xanthone and Phenazine Derivatives OR Non-covalent interaction >> DNA intercalation >> Coumarins OR Non-covalent interaction >> DNA intercalation >> DNA Intercalators with Carboxamide Side Chain OR Non-covalent interaction >> DNA intercalation >> Fused-Ring Nitroaromatics OR Non-covalent interaction >> DNA intercalation >> Quinones OR Non-specific OR Non-specific >> Incorporation into DNA/RNA, due to structural analogy with  nucleoside bases    OR Non-specific >> Incorporation into DNA/RNA, due to structural analogy with  nucleoside bases    >> Specific Imine and Thione Derivatives OR Radical OR Radical >> Generation of ROS by glutathione depletion (indirect) OR Radical >> Generation of ROS by glutathione depletion (indirect) >> Haloalkanes Containing Heteroatom OR Radical >> Radical mechanism by ROS formation OR Radical >> Radical mechanism by ROS formation >> Acridone, Thioxanthone, Xanthone and Phenazine Derivatives OR Radical >> Radical mechanism by ROS formation >> Polynitroarenes OR Radical >> Radical mechanism via ROS formation (indirect) OR Radical >> Radical mechanism via ROS formation (indirect) >> Conjugated Nitro Compounds OR Radical >> Radical mechanism via ROS formation (indirect) >> Coumarins OR Radical >> Radical mechanism via ROS formation (indirect) >> Flavonoids OR Radical >> Radical mechanism via ROS formation (indirect) >> Fused-Ring Nitroaromatics OR Radical >> Radical mechanism via ROS formation (indirect) >> Geminal Polyhaloalkane Derivatives OR Radical >> Radical mechanism via ROS formation (indirect) >> N-Hydroxylamines OR Radical >> Radical mechanism via ROS formation (indirect) >> Nitroaniline Derivatives OR Radical >> Radical mechanism via ROS formation (indirect) >> p-Aminobiphenyl Analogs OR Radical >> Radical mechanism via ROS formation (indirect) >> p-Substituted Mononitrobenzenes OR Radical >> Radical mechanism via ROS formation (indirect) >> Quinones OR Radical >> Radical mechanism via ROS formation (indirect) >> Specific Imine and Thione Derivatives OR Radical >> ROS formation after GSH depletion OR Radical >> ROS formation after GSH depletion >> Quinone methides OR SN1 OR SN1 >> Alkylation after metabolically formed carbenium ion species OR SN1 >> Alkylation after metabolically formed carbenium ion species >> Polycyclic Aromatic Hydrocarbon Derivatives OR SN1 >> Nucleophilic attack after carbenium ion formation OR SN1 >> Nucleophilic attack after carbenium ion formation >> N-Nitroso Compounds OR SN1 >> Nucleophilic attack after carbenium ion formation >> Pyrrolizidine Derivatives OR SN1 >> Nucleophilic attack after carbenium ion formation >> Specific Acetate Esters OR SN1 >> Nucleophilic attack after metabolic nitrenium ion formation OR SN1 >> Nucleophilic attack after metabolic nitrenium ion formation >> N-Hydroxylamines OR SN1 >> Nucleophilic attack after metabolic nitrenium ion formation >> p-Aminobiphenyl Analogs OR SN1 >> Nucleophilic attack after nitrenium and/or carbenium ion formation OR SN1 >> Nucleophilic attack after nitrenium and/or carbenium ion formation >> N-Nitroso Compounds OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> Conjugated Nitro Compounds OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> Fused-Ring Nitroaromatics OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> Nitroaniline Derivatives OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> Nitrobiphenyls and Bridged Nitrobiphenyls OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> Polynitroarenes OR SN1 >> Nucleophilic attack after reduction and nitrenium ion formation >> p-Substituted Mononitrobenzenes OR SN1 >> Nucleophilic substitution on diazonium ions OR SN1 >> Nucleophilic substitution on diazonium ions >> Specific Imine and Thione Derivatives OR SN1 >> SN1 reaction at nitrogen-atom bound to a good leaving group or on  nitrenium ion OR SN1 >> SN1 reaction at nitrogen-atom bound to a good leaving group or on  nitrenium ion >> N-Acyloxy(Alkoxy) Arenamides OR SN2 OR SN2 >> Acylation OR SN2 >> Acylation >> Specific Acetate Esters OR SN2 >> Acylation involving a leaving group  OR SN2 >> Acylation involving a leaving group  >> Geminal Polyhaloalkane Derivatives OR SN2 >> Acylation involving a leaving group  >> Haloalkane Derivatives with Labile Halogen OR SN2 >> Acylation involving a leaving group after metabolic activation OR SN2 >> Acylation involving a leaving group after metabolic activation >> Geminal Polyhaloalkane Derivatives OR SN2 >> Alkylation, direct acting epoxides and related OR SN2 >> Alkylation, direct acting epoxides and related >> Epoxides and Aziridines OR SN2 >> Alkylation, direct acting epoxides and related after cyclization OR SN2 >> Alkylation, direct acting epoxides and related after cyclization >> Nitrogen Mustards OR SN2 >> Alkylation, direct acting epoxides and related after P450-mediated metabolic activation OR SN2 >> Alkylation, direct acting epoxides and related after P450-mediated metabolic activation >> Haloalkenes with Electron-Withdrawing Groups OR SN2 >> Alkylation, direct acting epoxides and related after P450-mediated metabolic activation >> Polycyclic Aromatic Hydrocarbon Derivatives OR SN2 >> Alkylation, nucleophilic substitution at sp3-carbon atom OR SN2 >> Alkylation, nucleophilic substitution at sp3-carbon atom >> Haloalkane Derivatives with Labile Halogen OR SN2 >> Alkylation, ring opening SN2 reaction OR SN2 >> Alkylation, ring opening SN2 reaction >> Four- and Five-Membered Lactones OR SN2 >> Direct acting epoxides formed after metabolic activation OR SN2 >> Direct acting epoxides formed after metabolic activation >> Coumarins OR SN2 >> Direct acting epoxides formed after metabolic activation >> Quinoline Derivatives OR SN2 >> DNA alkylation OR SN2 >> DNA alkylation >> Alkylphosphates, Alkylthiophosphates and Alkylphosphonates OR SN2 >> DNA alkylation >> Vicinal Dihaloalkanes OR SN2 >> Internal SN2 reaction with aziridinium and/or cyclic sulfonium ion formation (enzymatic) OR SN2 >> Internal SN2 reaction with aziridinium and/or cyclic sulfonium ion formation (enzymatic) >> Vicinal Dihaloalkanes OR SN2 >> Nucleophilic substitution at sp3 Carbon atom OR SN2 >> Nucleophilic substitution at sp3 Carbon atom >> Haloalkanes Containing Heteroatom OR SN2 >> Nucleophilic substitution at sp3 Carbon atom >> Specific Acetate Esters OR SN2 >> Nucleophilic substitution at sp3 carbon atom after thiol (glutathione) conjugation OR SN2 >> Nucleophilic substitution at sp3 carbon atom after thiol (glutathione) conjugation >> Geminal Polyhaloalkane Derivatives OR SN2 >> SN2 at an activated carbon atom OR SN2 >> SN2 at an activated carbon atom >> Quinoline Derivatives OR SN2 >> SN2 at Nitrogen Atom OR SN2 >> SN2 at Nitrogen Atom >> N-acetoxyamines OR SN2 >> SN2 at sp3 and activated sp2 carbon atom OR SN2 >> SN2 at sp3 and activated sp2 carbon atom >> Polarized Haloalkene Derivatives OR SN2 >> SN2 reaction at nitrogen-atom bound to a good leaving group OR SN2 >> SN2 reaction at nitrogen-atom bound to a good leaving group >> N-Acetoxyamines OR SN2 >> SN2 reaction at nitrogen-atom bound to a good leaving group or nitrenium ion OR SN2 >> SN2 reaction at nitrogen-atom bound to a good leaving group or nitrenium ion >> N-Acyloxy(Alkoxy) Arenamides by DNA binding by OASIS v.1.3

Domain logical expression index: "h"

Referential boundary: The target chemical should be classified as Michael addition AND Michael addition >> P450 Mediated Activation to Quinones and Quinone-type Chemicals AND Michael addition >> P450 Mediated Activation to Quinones and Quinone-type Chemicals >> Arenes by DNA binding by OECD

Domain logical expression index: "i"

Referential boundary: The target chemical should be classified as Acylation OR Acylation >> Isocyanates and Isothiocyanates OR Acylation >> Isocyanates and Isothiocyanates >> Isothiocyanates OR Acylation >> P450 Mediated Activation to Isocyanates or Isothiocyanates OR Acylation >> P450 Mediated Activation to Isocyanates or Isothiocyanates >> Benzylamines-Acylation OR Acylation >> P450 Mediated Activation to Isocyanates or Isothiocyanates >> Formamides OR Michael addition >> P450 Mediated Activation of Heterocyclic Ring Systems OR Michael addition >> P450 Mediated Activation of Heterocyclic Ring Systems >> Furans OR Michael addition >> P450 Mediated Activation to Quinones and Quinone-type Chemicals >> Alkyl phenols OR Michael addition >> P450 Mediated Activation to Quinones and Quinone-type Chemicals >> Hydroquinones OR Michael addition >> P450 Mediated Activation to Quinones and Quinone-type Chemicals >> Methylenedioxyphenyl OR Michael addition >> Polarised Alkenes-Michael addition OR Michael addition >> Polarised Alkenes-Michael addition >> Alpha, beta- unsaturated aldehydes OR Michael addition >> Polarised Alkenes-Michael addition >> Alpha, beta- unsaturated esters OR Michael addition >> Polarised Alkenes-Michael addition >> Alpha, beta- unsaturated ketones OR Michael addition >> Quinones and Quinone-type Chemicals OR Michael addition >> Quinones and Quinone-type Chemicals >> Quinones OR No alert found OR Schiff base formers OR Schiff base formers >> Direct Acting Schiff Base Formers OR Schiff base formers >> Direct Acting Schiff Base Formers >> Mono aldehydes OR SN1 OR SN1 >> Carbenium Ion Formation OR SN1 >> Carbenium Ion Formation >> Allyl benzenes OR SN1 >> Iminium Ion Formation OR SN1 >> Iminium Ion Formation >> Aliphatic tertiary amines OR SN1 >> Nitrenium Ion formation OR SN1 >> Nitrenium Ion formation >> Aromatic azo OR SN1 >> Nitrenium Ion formation >> Aromatic nitro OR SN1 >> Nitrenium Ion formation >> Primary (unsaturated) heterocyclic amine OR SN1 >> Nitrenium Ion formation >> Primary aromatic amine OR SN1 >> Nitrenium Ion formation >> Secondary aromatic amine OR SN1 >> Nitrenium Ion formation >> Tertiary aromatic amine OR SN1 >> Nitrenium Ion formation >> Unsaturated heterocyclic azo OR SN2 OR SN2 >> SN2 at an sp3 Carbon atom OR SN2 >> SN2 at an sp3 Carbon atom >> Aliphatic halides by DNA binding by OECD

Domain logical expression index: "j"

Referential boundary: The target chemical should be classified as Non binder, without OH or NH2 group by Estrogen Receptor Binding

Domain logical expression index: "k"

Referential boundary: The target chemical should be classified as Non binder, MW>500 OR Strong binder, OH group by Estrogen Receptor Binding

Domain logical expression index: "l"

Referential boundary: The target chemical should be classified as No alert found by Protein binding by OASIS v1.3 ONLY

Domain logical expression index: "m"

Parametric boundary:The target chemical should have a value of log Kow which is >= 2.78

Domain logical expression index: "n"

Parametric boundary:The target chemical should have a value of log Kow which is <= 4.69

Conclusions:

2-phenylethyl propanoate (122-70-3) was predicted to not induce gene mutation in Salmonella typhimurium strains TA 1535, TA 1537, TA 98 , TA 100 TA 102 in the presence of S9 metabolic activation system and hence, according to the prediction made, it is not likely to classify as a gene mutant in vitro.

Executive summary:

Based on the prediction done using the OECD QSAR toolbox version 3.3 with log kow as the primary descriptor and considering the five closest read across substances, gene mutation was predicted for 2-phenylethyl propanoate (122-70-3) .The study assumed the use of Salmonella typhimurium strains TA 1535, TA 1537, TA 98 TA100 and TA 102  with S9 metabolic activation system. 2-phenylethyl propanoate as predicted to not induce gene mutation in Salmonella typhimurium strains TA 1535, TA 1537, TA 98 , TA 100and TA102 in the presence of S9 metabolic activation system and hence, according to the prediction made, it is not likely to classify as a gene mutant in vitro.

Based on the predicted result it can be concluded that the substance is considered to not toxic as per the criteria mentioned in CLP regulation.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Prediction model based estimation and data from read across chemical have been reviewed to determine the mutagenic nature of 2-phenylethyl propanoatem (122-70-3). The studies are as mentioned below

Based on the prediction done using the OECD QSAR toolbox version 3.3 with log kow as the primary descriptor and considering the five closest read across substances, gene mutation was predicted for 2-phenylethyl propanoate (122-70-3) .The study assumed the use of Salmonella typhimurium strains TA 1535, TA 1537, TA 98 TA100 and TA 102  with and without S9 metabolic activation system. 2-phenylethyl propanoate as predicted to not induce gene mutation in Salmonella typhimurium strains TA 1535, TA 1537, TA 98 , TA 100and TA102 in the presence and absence of S9 metabolic activation system and hence, according to the prediction made, it is not likely to classify as a gene mutant in vitro. Based on the predicted result it can be concluded that the substance is considered to not toxic as per the criteria mentioned in CLP regulation

Gene mutation toxicity was predicted for 2-phenylethyl propanoate (122-70-3) using the battery approach from Danish QSAR database (2017). The study assumed the use of Salmonella typhimurium bacteria in the Ames test. The end point for gene mutation has been modeled in the Danish QSAR using the three software systems Leadscope, CASE Ultra and SciQSAR. Based on predictions from these three systems, a fourth and overall battery prediction is made. The battery prediction is made using the so called Battery algorithm. With the battery approach it is in many cases possible to reduce “noise” from the individual model estimates and thereby improve accuracy and/or broaden the applicability domain.

In a Gene mutation toxicity study was performed by Errol Zeiger and Barry H. Margolin (Regulatory Toxicology and Pharmacology ,2000)) to determine the mutagenic nature of Benzyl phenylacetate (RA CAS no102-16-9; IUPAC name: Benzyl phenylacetate . The read across substances share high similarity in structure and log kow .Therefore, it is acceptable to derive information on mutation from the analogue substance. Gene mutation toxicity study was performed to determine the mutagenic nature of Benzyl phenylacetate. The study was performed as per the preincubation modification of the Salmonella/mammalian microsome mutagenicity (Ames) test. The chemicals were tested in a preincubation procedure in strains TA98 and TA100 without metabolic activation and with activation provided by Aroclor induced rat and hamster liver homogenates (S9). If a positive response was seen in one of these two strains, the strain/metabolic activation combination producing that response was repeated, and no further testing was performed. If no positive responses were seen, the chemical was tested in strains TA97 and TA1535. The plates were observed for a dose dependent increase in the number of revertants/plate. The combination of a questionable (?) and negative (-) response was considered negative (-); the combination of a weakly positive (+w) and negative response was considered questionable (?). Benzyl phenylacetate did not induce a dose dependent increase in the number of revertants in Salmonella typhimurium TA98, TA100, TA97 and TA1535 in the presence and absence of S9 metabolic activation system and hence it is not likely to classify as a gene mutant in vitro.

 

 In a Gene mutation toxicity study was performed by T.B. Adams et al (Food and Chemical Toxicology, 2005) to determine the mutagenic nature of Isopentyl phenylacetate (102-19-2); IUPAC name: 3-methylbutyl phenylacetate. The read across substances share high similarity in structure and log kow .Therefore, it is acceptable to derive information on mutation from the analogue substance. Genetic toxicity in vitro study was assessed for Isoamyl Phenylacetate (102-19-2) for its possible mutagenic potential .For this purpose Bacillus subtilis recombination assay was performed using BACILLUS SUBTILIS, H17 (rec +) and M45(rec -).The maximum dose of test chemical exposed was 20µL/disk. The test was evaluated by observing strong DNA damaging, DNA damaging, not DNA damaging, and reverse. The test chemical was considered to be to be non mutagenic in the REC assay. Hence Isoamyl Phenylacetate not likely to be classified as genetox in vitro.

 

Based on the data available for the target chemical and its read across substance and applying weight of evidence, it is concluded that 2-phenylethyl propanoatem (122-70-3) does not exhibit gene mutation in vitro. Hence the test chemical is not likely to classify as a gene mutant in vitro.

Justification for classification or non-classification

Thus based on the above annotation and CLP criteria for the target chemical and its read across substance and applying weight of evidence, it is concluded that 2-phenylethyl propanoatem (122-70-3) does not exhibit gene mutation in vitro. Hence the test chemical is not likely to classify as a gene mutant in vitro.