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Key Event: 2418
Key Event Title
Increased, phenotypic female-biased sex ratio
Short name
Biological Context
| Level of Biological Organization |
|---|
| Population |
Event Components
| Process | Object | Action |
|---|---|---|
| female sex determination | population of organisms | increased |
Key Event Overview
AOPs Including This Key Event
| AOP Name | Role of event in AOP | Point of Contact | Author Status | OECD Status |
|---|---|---|---|---|
| Activation, ERα leads to female-biased sex ratio via increased, differentiation to ovaries | AdverseOutcome | John Frisch (send email) | Under development: Not open for comment. Do not cite |
Taxonomic Applicability
| Term | Scientific Term | Evidence | Link |
|---|---|---|---|
| Animals | Metazoa | Moderate | NCBI |
Life Stages
| Life stage | Evidence |
|---|---|
| Development | Moderate |
Sex Applicability
| Term | Evidence |
|---|---|
| Unspecific | Moderate |
Key Event Description
Sex ratio is determined by the proportion of females to males in a population, with increased phenotypic female biased sex-ratio reflecting an increased proportion of females to males.
How It Is Measured or Detected
Sex ratio is determined by the proportion of females to males in a population. Verification of phenotypic sex can be done by histological examination of reproductive organs.
Domain of Applicability
Life Stage: Development.
Sex: Applies to females and males.
Taxonomic: Possible in any animal species that has females and males.
Regulatory Significance of the Adverse Outcome
Increased female biased sex ratio is an adverse outcome monitored in Endocrine Disruptor Screening Program (EDSP) protocol (US EPA 1998).
References
US Environmental Protection Agency (EPA). 1998. Health Effects Test Guidelines OPPTS 870.3800 Reproduction and Fertility Effects https://ntp.niehs.nih.gov/sites/default/files/iccvam/suppdocs/feddocs/epa/epa_870_3800.pdf (retrieved 19 Jan 2026)
NOTE: Italics indicate edits from John Frisch April 2026. A full list of updates can be found in the Change Log on the View History page.