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Related Concept Videos

The Ratio of X Chromosome to Autosomes02:45

The Ratio of X Chromosome to Autosomes

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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.  
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female...
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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.
Near the gonadal ridges, two duct systems are present: the mesonephric ducts (Wolffian ducts) and paramesonephric ducts (Müllerian ducts). These ducts form the basis for the...
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The Y Chromosome Determines Maleness02:19

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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
Around 300 million years ago, the two sex chromosomes diverged from two identical autosomal chromosomes. Over time, the Y chromosome has lost most of its genes, shrinking in size....
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Background and Environment Affect Phenotype02:27

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Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...
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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.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...
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Natural Selection and Mating Preferences01:06

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The principle of natural selection posits that organisms better adapted to their environment are more likely to survive and reproduce. This principle is closely intertwined with mating preferences, a key aspect of sexual selection, which evolutionary psychologists believe is driven by instincts to propagate one's genes. Such instincts significantly influence mating behaviors and preferences between genders.
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Related Experiment Video

Updated: Sep 24, 2025

Dissection of Larval Zebrafish Gonadal Tissue
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Evolution: Various routes to sex determination.

Manus M Patten1

  • 1Department of Biology, Georgetown University, Washington, DC, USA.

Current Biology : CB
|May 10, 2022
PubMed
Summary

Researchers studied the African pygmy mouse, Mus minutoides, to understand its complex sex chromosome system. This analysis combined empirical data and theoretical models to reveal its evolutionary path.

Area of Science:

  • Evolutionary biology
  • Genetics
  • Mammalian evolution

Background:

  • The African pygmy mouse (Mus minutoides) possesses a unique and complex sex chromosome system.
  • Understanding the evolution of sex chromosomes provides insights into speciation and reproductive biology.

Purpose of the Study:

  • To reconstruct the evolutionary history of the sex chromosome system in Mus minutoides.
  • To analyze the genetic and theoretical factors driving the diversification of sex chromosomes.

Main Methods:

  • Integration of empirical genetic data.
  • Application of theoretical evolutionary analyses.
  • Comparative genomics and phylogenetic reconstruction.

Main Results:

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  • Detailed reconstruction of the step-by-step evolutionary changes.
  • Identification of key genetic events shaping the sex chromosomes.
  • Elucidation of the mechanisms leading to the current elaborate system.

    • Conclusions:

    • The study provides a comprehensive model for sex chromosome evolution in mammals.
    • Findings shed light on the adaptability and diversification of the Mus genus.
    • The complex system of Mus minutoides offers a unique case study for evolutionary genetics.