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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.

Pedigree Analysis

Pedigree Analysis

X-linked Traits

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 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....

Development of the Sexual Organs in the Embryo and Fetus

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.
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...

Nondisjunction

Nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.

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Related Experiment Video

Updated: Nov 8, 2025

Urethroplasty with Pedicled Tunica Vaginalis for the Treatment of Long-segment Anterior Urethral Stricture Caused by Lichen Sclerosus of Glans Penis

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Published on: October 18, 2024

Hypospadias in ring X syndrome.

Hatem Elghezal¹, Khowla Alfayez¹, Inesse Ben Abdallah¹

¹Cytogenetics and Molecular Genetics Division, Prince Sultan Military Medical City, Riyadh, Saudi Arabia.

European Journal of Medical Genetics

|April 19, 2021

Summary

Ring X chromosome is a rare anomaly in males, typically incompatible with survival. This study details a unique case in a male child, identifying genetic deletions and duplications that may explain survival and specific developmental features.

Keywords:

Hypospadias Inv dup del Ring X chromosome SHOX deletion

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Area of Science:

Genetics
Human Biology
Chromosomal Abnormalities

Background:

Ring X chromosome (r(X)) is a rare chromosomal anomaly, primarily observed in females with Turner syndrome, often in mosaic form due to mitotic instability.
In males, large nullisomy for X chromosome material is generally considered incompatible with survival, making male r(X) cases exceptionally rare.

Observation:

This report details a four-year-old male with a ring X chromosome, characterized by Karyotype, Fluorescence In Situ Hybridization (FISH), and array Comparative Genomic Hybridization (aCGH).
The patient presented with short stature, microcephaly, and hypospadias.

Findings:

Molecular investigations revealed a 923 Kb terminal deletion on the pseudoautosomal region 1 (PAR1), encompassing the SHOX gene, followed by a 2.4 Mb duplication.
The presence of a second copy of the deleted genes in the Y chromosome PAR1 region likely explains the survival in this male r(X) case.
Short stature is attributed to SHOX gene deletion and "ring syndrome" effects, while hypospadias may result from the duplication involving the PRKX gene.

Implications:

This case expands the understanding of male ring X chromosome survival, highlighting the role of genetic compensation mechanisms.
The findings suggest that deletions within PAR1, particularly involving the SHOX gene, contribute to short stature in male r(X) individuals.
The associated duplication provides a potential genetic basis for hypospadias in this rare condition, offering insights into urogenital development.