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Related Concept Videos

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”.
Sex-linked Disorders01:43

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 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...
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,...
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...
Dosage Compensation02:50

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...

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Ploidy Manipulation of Zebrafish Embryos with Heat Shock 2 Treatment
11:19

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Unusual distribution of Zfy and Zfx sequences on the sex chromosomes of the wood lemming, a species exhibiting XY sex

Y F Lau1, T L Yang-Feng, B Elder

  • 1Division of Cell and Developmental Genetics, Veterans Administration Medical Center, University of California, San Francisco 94121.

Cytogenetics and Cell Genetics
|January 1, 1992
PubMed
Summary

Sex reversal in wood lemmings is linked to a mutated X chromosome (X*). This X* chromosome disrupts normal male sex determination, causing X*Y individuals to develop as females, unlike typical XY males.

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Area of Science:

  • Genetics
  • Developmental Biology
  • Mammalian Sex Determination

Background:

  • Wood lemmings (Myopus schisticolor) exhibit natural sex reversal due to a variant X chromosome (X*).
  • X*Y individuals develop as females, while XY individuals are normal males.
  • This phenomenon points to a complex sex-determination system involving X and Y chromosomes.

Purpose of the Study:

  • To investigate the genetic basis of sex reversal in wood lemmings.
  • To map the location of ZFX and ZFY genes in relation to the sex-determining genes.
  • To explore the expression patterns of ZFX and ZFY genes in different tissues.

Main Methods:

  • Chromosome mapping using in situ hybridization.
  • DNA sequence analysis (Southern blot).
  • Gene expression analysis (Northern hybridization).

Main Results:

  • Wood lemming ZFX sequences map to Xp12-p11, near the X* breakpoint.
  • ZFX and ZFX* genes express similar transcripts in somatic tissues.
  • Multiple, transcriptionally inactive ZFY copies are found on the Y chromosome.

Conclusions:

  • The chromosomal location of ZFX suggests it or a linked gene may be the major sex-determining gene (Tdx).
  • The X* chromosome's Tdx may fail to interact with the Y-linked Tdy, causing female development in X*Y individuals.
  • The role of ZFY gene expression in wood lemming spermatogenesis requires further investigation.