Committee Meeting Fall 2025

Cross-Sex Genetic Correlation

How strongly the same genes affect a characteristic in both males and females. High values mean the sexes share the same underlying genes for that characteristic.

Evolution

Changes in inherited characteristics of a population over time

Sexual Dimorphism

Physical differences between males and females of the same species (like size, coloration, or antlers).

Intralocus Sexual Conflict

When the same gene produces different ideal outcomes for males versus females, creating a genetic tug-of-war within the genome.

Interlocus Sexual Conflict

When separate genes in males and females are locked in an evolutionary arms race (like male persistence vs. female resistance to mating).

Fitness Optimum

The ideal value of a characteristic that gives the highest reproductive success.

Fitness Surface

A landscape showing which combinations of characteristics produce the highest reproductive success (peaks) and lowest success (valleys).

Trait Distribution

The pattern of how a measurable characteristic varies across individuals in a population (its average, spread, and shape).

Relative Fitness

How well an individual reproduces compared to others in the population.

Trait

Any measurable characteristic of an organism (like height, beak size, or flowering time).

Fitness

The number of surviving offspring an individual produces; a measure of reproductive success.

Partially Resolved Sexual Conflict

When males and females have evolved some independence in their genes but still share enough that neither can reach their ideal characteristics.

Fully Resolved Sexual Conflict

When males and females have completely separate control over genes affecting a characteristic, allowing each to reach their ideal independently.

Gene

A unit of hereditary information that codes for a particular characteristic or function.

Locus

A specific location on a chromosome where a particular gene sits (plural: loci).

Allele

Different versions of the same gene (like blue vs. brown eye color versions).

Genetic Variation

Differences in DNA sequences between individuals that can be passed to offspring.

Genome

The complete set of DNA instructions in an organism

Inheritance

The passing of characteristics from parents to offspring through genes

Absolute Fitness

The actual number of surviving offspring an individual produces (not compared to others).

Common Theorized Constraints of Sexual Dimorphism

1. Shared Genome/Genetic Architecture: Males and females share nearly identical genomes, so genes affecting a characteristic in one sex often affect it in the other, preventing independent optimization.

2. Cross-Sex Genetic Correlations: Strong positive genetic correlations between sexes mean selection on one sex causes correlated responses in the other, limiting divergence.

3. Pleiotropic Gene Effects: Single genes often affect multiple characteristics, so changing one trait to benefit one sex may harm other traits or the other sex.

4. Developmental Constraints: Males and females share the same developmental pathways early in life, limiting how differently they can develop later.

5. Lack of Sex-Specific Genetic Variation: Insufficient genetic variation that affects only one sex; without raw material for sex-specific evolution, dimorphism cannot evolve.

6. Mutation Load: Sexually antagonistic alleles (beneficial in one sex, harmful in the other) accumulate and persist, preventing populations from reaching sex-specific optima.

7. Linkage and Chromosomal Architecture: Physically linked genes may constrain independent evolution if beneficial alleles for one sex are linked to harmful alleles for the other.

8. Cost of Trait Expression: Extreme dimorphism may be too costly to produce or maintain, especially if resources are limited for development and reproduction.

9. Opposing Selection Pressures: Natural selection for survival may favor similar phenotypes in both sexes, counteracting sexual selection for dimorphism.

10. Limited Evolutionary Time: Insufficient time has passed for complete resolution of sexual conflict through evolution of sex-limited expression.

Phenotype

The observable physical and behavioral characteristics of an organism.

Genotype

The specific combination of gene versions (alleles) an individual carries

Trait Divergence

When a characteristic evolves to become increasingly different between populations or sexes over time.

Autosome

Any chromosome that isn't a sex chromosome

Disruptive Selection

When extreme values of a characteristic are favored over intermediate values, potentially splitting a population.

Directional Selection

When one extreme of a characteristic is consistently favored, shifting the population average in that direction.

Balancing Selection

Forces that maintain multiple versions of a gene in a population (like when heterozygotes have advantages).

Sexually Antagonist Selection

When different values of a characteristic are favored in males versus females.

Breeding Value

The genetic worth of an individual as a parent, based on how much better or worse its offspring perform on average.

Autosomal Breeding Value

The parental genetic worth based only on chromosomes that aren't sex chromosomes.

X-linkage

When a gene is located on the X chromosome, causing different inheritance patterns in males and females.

Y-linkage

When a gene is located on the Y chromosome, passing only from fathers to sons.

Principal Component Analysis

A statistical method that identifies the main patterns of variation in multiple correlated measurements.

First Principal Component

The single axis that captures the largest amount of variation in a dataset.

Second Principal Component

The next most important axis of variation, independent of the first, capturing remaining patterns.

Sex-Limited

A characteristic that appears in only one sex, even though both sexes carry the genes for it (like antlers or lactation).

Sex-Specific

Characteristics controlled by genes found only on sex chromosomes, or traits expressed differently due to sex.

Breeder's Equation

A formula predicting how much a population will change in one generation: response to selection equals heritability times selection strength.

Cross-sex Genetic Covariance v. Correlation

Covariance measures the absolute shared genetic variation between sexes for a characteristic; correlation standardizes this (from -1 to +1) to show the strength of the relationship regardless of scale.

Additive Genetic Variance

The portion of genetic variation that parents reliably pass to offspring; determines how predictably a population responds to selection.

Heritability

The proportion of variation in a characteristic that is due to genetic differences between individuals (ranges from 0 to 1).

Selection Differential

The difference between the average value of a characteristic in selected parents versus the whole population before selection.

Selection Intensity

The strength of selection expressed in standardized units; how many standard deviations the selected parents differ from the population average.

G-matrix

A table showing genetic variances for multiple characteristics and how they genetically covary with each other.

Selection Pressures

Environmental or reproductive forces that favor certain characteristics over others, causing populations to change.

Sexual Conflict

When the optimal value of a characteristic differs between males and females, creating opposing evolutionary pressures.

X-linked Genetic Effects

Influences on characteristics caused by genes located on the X chromosome, which follow special inheritance patterns.

Development

The process by which an organism grows from a fertilized egg to its adult form.

Gene Expression

The process of turning genetic information into functional products (proteins or RNA) that affect the organism.

Sex-linkage

The pattern of inheritance for genes located on sex chromosomes (X or Y), which differs between males and females.

Dominance

When one version of a gene masks the effect of another version in individuals carrying both.

Variance

A statistical measure of how spread out values are in a population; the average of squared deviations from the mean.

Covariance

A measure of how two characteristics vary together; positive values mean they tend to increase together, negative means one increases as the other decreases.

Correlation

A standardized measure (from -1 to +1) of how strongly two characteristics are related to each other.

Population

A group of interbreeding individuals of the same species living in the same area at the same time.

Adaptive Landscape

A visualization where "height" represents how well-adapted different combinations of characteristics are in a given environment.

Double First Cousin Breeding Design

A mating scheme where offspring share all four grandparents, used to estimate genetic parameters by creating specific relatedness patterns.

Urban Area

A city or town environment characterized by high human population density, buildings, and modified landscapes.

Urban Gradient

The gradual change in environmental conditions from rural areas through suburbs to city centers.

Environmental Pressures

Non-living or living factors in the surroundings that affect survival and reproduction (like temperature, predators, or resource availability).

Fecundity Selection

Reproductive success based on the number of offspring produced, rather than survival alone.

Viability Selection

Reproductive success based on survival to reproductive age, rather than number of offspring produced.

Ecology

The study of how organisms interact with each other and their physical environment.

Red Queen Hypothesis

The idea that species must constantly evolve just to maintain their current fitness level, because other species (parasites, predators, competitors) are also evolving.

Type II Error

Failing to detect a real effect or difference when one actually exists; a "false negative" in statistical testing.

Type I Error

Detecting an effect or difference that doesn't actually exist; a "false positive" in statistical testing.

p-value

The probability of observing results as extreme as those found, if there were actually no real effect; commonly used threshold is 0.05.

Credible Interval

A range of values that likely contains the true value of a parameter, based on probability; the Bayesian equivalent of a confidence interval.

Natural Selection

The process where heritable characteristics that improve survival or reproduction become more common in populations across generations, because individuals with advantageous characteristics leave more offspring than those without them.

Sexual Selection

Selection based on competition for mates or mate choice, rather than survival; often produces elaborate ornaments or weapons.

Linkage Disequilibrium

When two genes are inherited together more often than expected by chance, usually because they're close together on a chromosome.

Genetic Drift

Random changes in gene frequencies from one generation to the next, especially strong in small populations.

Genetic Hitchhiking

When a neutral or slightly harmful gene increases in frequency because it's physically close to a beneficial gene being selected for.

Mutation

A random change in DNA sequence that creates new versions of genes; the ultimate source of all new genetic variation.

Dosage Compensation

Biological mechanisms that equalize the expression of X chromosome genes between males (XY) and females (XX), despite females having twice as many copies.

Pleiotropy

a genetic phenomenon where a single gene influences multiple, distinct phenotypic traits

Narrow-sense heritability (ℎ^2)

proportion of the phenotypic variance that can be attributed to additive genetic variance

Broad-sense heritability (H^2)

the proportion of total phenotypic variation in a trait that is due to all genetic variation, including additive, dominance, and epistasis effects