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Key Event: 2418

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Increased, phenotypic female-biased sex ratio

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
Increased, female-biased sex ratio
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization
Population

Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Process Object Action
female sex determination population of organisms increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
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

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
Animals Metazoa Moderate NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help
Life stage Evidence
Development Moderate

Sex Applicability

An indication of the the relevant sex for this KE. More help
Term Evidence
Unspecific Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

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

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

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

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

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

An AO is a specialised KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help

Increased female biased sex ratio is an adverse outcome monitored in Endocrine Disruptor Screening Program (EDSP) protocol (US EPA 1998).  

References

List of the literature that was cited for this KE description. More help

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.