From the origin of sex-determining factors to the evolution of sex-determining systems

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Updated: May 29, 2026

Dissection of Larval Zebrafish Gonadal Tissue
10:43

Dissection of Larval Zebrafish Gonadal Tissue

Published on: April 26, 2017

Tobias Uller1, Heikki Helanterä

  • 1Edward Grey Institute, Department of Zoology, University of Oxford Oxford OX1 3PS United Kingdom. TOBIAS.ULLER@ZOO.OX.AC.UK

The Quarterly Review of Biology
|September 30, 2011
PubMed

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Development of the Sexual Organs in the Embryo and Fetus

Development of the reproductive organs in an embryo starts from a bipotential state. This means the early embryo can develop either male or female reproductive organs. The formation of these organs begins with the growth of gonadal ridges that arise from the intermediate mesoderm during the fifth week of development.
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The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
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The Y Chromosome Determines Maleness

The Y chromosome is a sex chromosome found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human males have one X chromosome and one Y chromosome. In these organisms, the presence or absence of the Y chromosome determines the development of male traits.
Evolution
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X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
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The reproductive system generates offspring, ensuring the survival of the species. In humans, the reproductive system is complex and involves a variety of organs and hormones that work together to ensure successful reproduction.
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