# Sex-ratio bias induced by mutation

## TL;DR

This paper explores how mutation influences sex ratio bias in species, showing that mutation-induced fluctuations can systematically shift the sex ratio away from equality, and provides a method to estimate mutation rates from observed ratios.

## Contribution

It demonstrates that mutation causes systematic deviations from the 1:1 sex ratio and introduces a way to estimate mutation rates based on observed sex ratios.

## Key findings

- Mutation causes fluctuations that bias sex ratios away from 1:1.
- The model links observed sex ratios to mutation rates.
- Mutation effects can be systematically quantified.

## Abstract

A question in evolutionary biology is why the number of males is approximately equal to that of females in many species, and Fisher's theory of equal investment answers that it is the evolutionarily stable state. The Fisherian mechanism can be given a concrete form by a genetic model based on the following assumptions: (1) Males and females mate at random. (2) An allele acts on the father to determine the expected progeny sex ratio. (3) The offspring inherits the allele from either side of the parents with equal probability. The model is known to achieve the 1:1 sex ratio due to the invasion of mutant alleles with different progeny sex ratios. In this study, however, we argue that mutation plays a more subtle role in that fluctuations caused by mutation renormalize the sex ratio and thereby keep it away from 1:1 in general. This finding shows how the sex ratio is affected by mutation in a systematic way, whereby the effective mutation rate can be estimated from an observed sex ratio.