Darwin defined sexual selection as selection based solely on reproduction success. The selection pressure has endowed males to display their sexual ornaments as a visible sign for dominance to attract females. Female sexual ornaments have not received the interest as male sexual ornaments, but recently it has been shown that sexual ornaments are not exclusive to males. Enlarged ornaments in females have equally to males evolved through intra-sexual competition.

The comb represents the female sexual ornament in the chicken and it has been proven to be an honest ornament. “Females are not expected to invest in ornamentation unless the fitness benefits of the ornament exceed those derived from investing the resources directly into offspring” LeBas et al. (2003). The information displayed as the size of the comb is directly correlated to fecundity. Females that carry a large comb will produce larger and more eggs, than a hen that has a smaller comb.

The genes underlying the traits for comb size and egg size are not yet fully understood. The traits are quantitative and the Quantative Trait Loci (QTL) for comb size and egg size has been found on chromosome 1 and 3. It is not yet known if the QTLs for comb and egg are very closely linked, since the trait is honest, or if the phenotypical effects are pleiotropic. In this project I have used an 8 th generation Advanced Intercross Line bred to maintain genotypic and phenotypic diversity, to ensure a greater combination of alleles for QTL detection. The project attempts to measure the females’ combs, measuring weight, area and length and correlate that to the production and weight of the eggs. The aim is to, by observing phenotypical traits, understand the genetical background.  

Collecting eggs during two weeks to measure productivity.

Three egg measurements:

1. Number of eggs
2. Mean egg weight
3. Total egg mass

Photographing comb for two measurements:

1. Length in cm
2. Area in sqcm

Third size indicator, weighing comb postmortem