This term is restricted to autosomal traits, and should not be confused with sex-linked characteristics, which have to do with genetic differences on the sex chromosomes (see sex-determination system).
However, the resulting phenotypes caused by sex-limited genes are present in only one sex and can be seen prominently in various species that typically show high sexual dimorphism.
[2] Sex-limited genes are responsible for sexual dimorphism, which is a phenotypic (directly observable) difference between males and females of the same species regardless of genotype.
Sex-limited genes are also responsible for some female beetles' inability to grow exaggerated mandibles,[5] research that is discussed in detail later in this article.
Sex-limited genes were first hypothesized by Charles Darwin and though he was unsuccessful in distinguishing the previously mentioned sex-linked traits, his hypothesis was the starting point for future study of the subject.
Modern research suggests that a substantial portion of the expression of sex-limited genes and sexual dimorphism may be influenced by certain epigenetic marks.
[3] The idea of sex-limited genes was initially developed by Charles Darwin in 1871 in his book The Descent of Man and Selection in Relation to Sex.
One of the more notable examples is John H. Gerould's "Inheritance of White Wing Color, a Sex-Limited (Sex-Controlled) Variation in Yellow Pierid Butterflies," published in Genetics in 1923 (and edited slightly in 1924).
After these groundbreaking works, papers continue to be published further exploring the causes, mechanisms, evolutionary advantages, and more of sex-limited genes.
The genetic study of sexual dimorphism, published in Evolution, hypothesizes two methods which leads to different ornamental characteristics in male and female birds.
The concept of this study was to examine female hybrids from species where males displayed different types of ornamental traits (elongated feathers, wattles, color patches).
The methods and materials of the experiment are discussed in detail in the paper, but the important result that emerged was that NO female hybrids expressed any of the ornamental traits found in the parent males.
These conclusions make it likely that at least some male-specific (thus, sex-limited) genes cue their expression by hormone levels, such as threshold ratios of estrogen and testosterone.
Thus, selection on males for sex-limited traits such as increased size (elephant seals) and weaponry (claws on fiddler crabs, horns on rhinoceros beetles) will change direction with fluctuation in population density.
One of the key principles of sex-biased gene expression that Parsch and Ellegren stressed in their paper in February 2013[13] is that of rapid evolution.
This makes sense in the context of genes with reproductive function evolving more quickly, a generally observed pattern in evolutionary biology.
By following a natural population of red-billed gulls for 46 years, Teplitsky et al. came to an unexpected conclusion - while laying date (aka breeding time) is only expressed in females, the trait is only heritable in males.
Specifically, this affects whether alleles are imprinted in consecutive generations with different evolutionary trajectories (under the same selection fitnesses) arising purely due to sex-limited epigenetics.
In humans, the process of X chromosome inactivation occurs in the beginning stages of development which is one of the main reasons why this topic has been challenging to study.
Thus sex-limited epigenetic traits may have played a pivotal role in the evolution of mammals and other species, particularly as a mechanism to ameliorate intralocus conflict between the sexes.