Sex Chromosomes: A Review of the Genetic Basis of Sexual Dimorphism
In humans and other mammals, sex is determined by the presence or absence of certain genetic material. This material is found in the form of chromosomes, and the two primary sex chromosomes are the X and Y chromosomes. This review article provides an overview of sex chromosomes, including their history, structure, and function, as well as their role in sexual dimorphism.
History
The first recorded discovery of sex chromosomes was made by Nettie Stevens in 1905. Stevens, using the mealworm species, found that males had an X and a Y chromosome, while females had two X chromosomes. This was the first time that the presence of sex chromosomes was directly observed. Since then, research has revealed that sex chromosomes are present in many species, including humans, and that their structure and function are highly conserved across species.
Structure
Sex chromosomes are composed of both coding and non-coding DNA. The X chromosome has more than 1000 genes, while the Y chromosome has fewer than 100. In addition, the Y chromosome is significantly smaller than the X chromosome. The X chromosome contains genes that are involved in many biological processes, such as development, metabolism, and immunity. The Y chromosome, on the other hand, has genes that are involved primarily in male fertility.
Function
The primary function of sex chromosomes is to determine the sex of an individual. In humans, the presence of a Y chromosome results in male development, while the absence of a Y chromosome results in female development. Furthermore, the function of sex chromosomes is not limited to sexual dimorphism. For instance, the X chromosome is also involved in the regulation of gene expression, as well as in the functioning of the immune system.
Role in Sexual Dimorphism
Sex chromosomes are responsible for the development of the phenotypic differences between males and females. This is because they contain the genetic material necessary for the development of the sex-specific characteristics. The presence of a Y chromosome leads to the development of male characteristics, such as facial and body hair, and the absence of a Y chromosome leads to the development of female characteristics, such as breasts and a wider pelvis. Furthermore, sex chromosomes are also responsible for the differences in reproductive function between males and females, as they contain the genetic material necessary for the development of the reproductive organs.
Conclusion
In conclusion, sex chromosomes are responsible for the determination of sex, as well as the development of the phenotypic differences between males and females. This review article has provided an overview of sex chromosomes, including their history, structure, and function, as well as their role in sexual dimorphism.
References
Burgoyne, P. S. (2016). Chromosomes and sex determination. In Encyclopedia of Reproduction (pp. 531–542). Academic Press.
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Ohno, S. (1967). Sex chromosomes and sex-linked genes. Science, 156(3774), 397–405.
Stevens, N. (1905). Sex in the mealworm (Tenebrio molitor). Science, 22(570), 545–547.