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Related Concept Videos

X and Y Chromosomes02:32

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...
X-Inactivation01:58

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.
X-inactivation01:58

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.
X-linked Traits01:19

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
X-linked Traits01:19

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
The Ratio of X Chromosome to Autosomes02:45

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...

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Related Experiment Video

Updated: Jun 28, 2026

Strategies for Assessing Autistic-Like Behaviors in Mice
07:38

Strategies for Assessing Autistic-Like Behaviors in Mice

Published on: September 20, 2024

Autism-lessons from the X chromosome.

Elysa J Marco1, David H Skuse

  • 1Behavioral and Brain Sciences Unit, Institute of Child Health, London, UK.

Social Cognitive and Affective Neuroscience
|November 6, 2008
PubMed
Summary

Autism spectrum disorder (ASD) prevalence is increasing, with X-linked genes potentially explaining the male predominance. Studying genetic disorders highlights ASD as a broad phenotype influenced by multiple genes and epigenetic factors.

Area of Science:

  • Neurogenetics
  • Developmental Disorders
  • Genetics

Background:

  • Recognized cases of autism spectrum disorders (ASD) are increasing globally.
  • The male predominance in ASD (4:1 to 10:1) suggests a role for sex-linked genetic factors.
  • Understanding the genetic underpinnings of ASD is crucial for improved diagnosis and treatment.

Purpose of the Study:

  • To review the role of X-linked genes in autism spectrum disorders.
  • To explore how specific genetic disorders illuminate the genetic architecture of ASD.
  • To discuss the implications of X-linked genetic research for understanding ASD etiology.

Main Methods:

  • Review of scientific literature on X-linked genetic disorders and autism.
  • Analysis of genetic conditions including aneuploidies, trinucleotide expansions, and nucleotide mutations.

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  • Examination of epigenetic factors like imprinting and X-inactivation.

    • Main Results:

    • X-linked genes are implicated in the male vulnerability observed in ASD.
    • Genetic disorders such as Turner syndrome, Klinefelter syndrome, Fragile X syndrome, Rett Syndrome, and mutations in Neuroligins and SLC6A8 provide insights into ASD phenotypes.
    • ASD should be viewed as a broad phenotype, not a single entity, influenced by multiple genes and epigenetic factors.

    Conclusions:

    • X-linked genetic disorders offer valuable models for understanding autism spectrum disorders.
    • Multiple genes and epigenetic mechanisms contribute to the manifestation and severity of ASD.
    • Further research into social cognition phenotypes and X-linked neurogenetics will enhance our understanding of ASD.