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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-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”.
Pedigree Analysis01:35

Pedigree Analysis

Overview
The Y Chromosome Determines Maleness02:19

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,...
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.

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Exploring X Chromosomal Aberrations in Ovarian Cells by Using Fluorescence In Situ Hybridization
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Published on: April 7, 2023

Testing for association on the X chromosome.

David Clayton1

  • 1Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrookes's Hospital, Cambridge, UK. david.clayton@cimr.cam.ac.uk

Biostatistics (Oxford, England)
|April 29, 2008
PubMed
Summary

This study introduces new statistical tests for X-linked genotype-phenotype associations in mixed-sex groups. These methods do not require Hardy-Weinberg equilibrium and improve power when phenotypes differ between sexes.

Keywords:
Genetic association studies

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Area of Science:

  • Genetics
  • Statistical Genetics
  • Population Genetics

Background:

  • Testing genotype-phenotype associations for X-linked loci in mixed-sex samples is challenging.
  • Existing methods often assume Hardy-Weinberg equilibrium and may lack power due to sex stratification.

Purpose of the Study:

  • To develop novel statistical tests for X-linked genotype-phenotype association in mixed-sex samples.
  • To propose methods that do not assume Hardy-Weinberg equilibrium and are robust to sex-specific phenotypic variation.

Main Methods:

  • Proposed 1 and 2 degree-of-freedom association tests.
  • Treated males as homozygous females for analytical purposes.
  • Developed methods that do not assume Hardy-Weinberg equilibrium.

Main Results:

  • The proposed tests remain valid even when phenotype varies between sexes, as long as allele frequencies are consistent.
  • The new methods avoid power loss associated with stratifying analyses by sex.
  • The approach is applicable to mixed-sex samples without assuming Hardy-Weinberg equilibrium.

Conclusions:

  • The developed statistical tests offer a more robust and powerful approach for analyzing X-linked genotype-phenotype associations in mixed-sex populations.
  • These methods address limitations of previous approaches, particularly concerning Hardy-Weinberg equilibrium and sex-specific phenotypes.