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Dosage Compensation

Dosage Compensation

In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
In addition to sexual development, the X chromosome has genes involved in autosomal functions such as brain development and the immune system. Therefore, males and females with distinct numbers of X chromosomes will have...

The Ratio of X Chromosome to Autosomes

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.
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...

X and Y Chromosomes

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.
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...

The Y Chromosome Determines Maleness

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
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. Today,...

Sex-linked Disorders

Sex-linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.

X-Inactivation

X-Inactivation

The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, one might expect females to produce twice as many of the proteins, with undesirable results.

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Related Experiment Video

Updated: Jul 10, 2026

Slide Preparation Method to Preserve Three-dimensional Chromatin Architecture of Testicular Germ Cells

Slide Preparation Method to Preserve Three-dimensional Chromatin Architecture of Testicular Germ Cells

Published on: January 10, 2014

Sex chromosome complement regulates habit formation.

Jennifer J Quinn¹, Paul K Hitchcott, Elizabeth A Umeda

¹Division of Molecular Psychiatry, Yale University, Connecticut Mental Health Center Abraham Ribicoff Research Facilities, 34 Park Street, New Haven, Connecticut 06508, USA.

Nature Neuroscience

|October 24, 2007

Summary

Sex chromosomes, not just hormones, influence brain function. Female (XX) mice demonstrated quicker learning of food-rewarded tasks compared to male (XY) mice, irrespective of their gonads.

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Last Updated: Jul 10, 2026

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Area of Science:

Neuroscience
Genetics
Behavioral Science

Background:

Sex differences in brain function are often linked to gonadal hormones.
However, sex chromosome genes can directly impact brain sexual dimorphisms independently of hormones.

Purpose of the Study:

To investigate the direct role of sex chromosome complement (XX vs. XY) in brain function, separate from gonadal influences.
To determine if sex chromosome complement affects instrumental habit formation.

Main Methods:

Utilized genetically modified mice where sex chromosome complement (XX or XY) and gonadal sex (ovaries or testes) could be independently manipulated.
Assessed performance in a food-reinforced instrumental habit formation task.

Main Results:

Mice with a female sex chromosome complement (XX) exhibited significantly faster habit formation compared to mice with a male sex chromosome complement (XY).
This effect was observed irrespective of the gonadal phenotype (ovaries or testes).

Conclusions:

Sex chromosome complement plays a direct role in modulating specific brain functions, such as learning and habit formation.
These findings highlight a mechanism for sex differences in brain and behavior that is independent of gonadal hormones.