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Related Concept Videos

The Y Chromosome Determines Maleness02:19

The Y Chromosome Determines Maleness

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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....
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The Ratio of X Chromosome to Autosomes02:45

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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...
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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.
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Dosage Compensation02:50

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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.
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Lampbrush Chromosomes01:51

Lampbrush Chromosomes

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In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps.
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops...
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Genetics of Speciation

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Speciation is the evolutionary process resulting in the formation of new, distinct species—groups of reproductively isolated populations.
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Sex Chromosome Evolution: Hallmarks and Question Marks.

Paul A Saunders1, Aline Muyle1

  • 1CEFE, University of Montpellier, CNRS, EPHE, IRD, Montpellier, France.

Molecular Biology and Evolution
|October 17, 2024
PubMed
Summary

Sex chromosomes evolve diverse forms across species, with new technologies revealing common evolutionary paths. However, the ultimate reasons for this diversity and the existence of sex chromosomes remain key research questions.

Keywords:
degenerationdosage compensationevolutionary rategene contentrearrangementrecombination suppressionturnover

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Area of Science:

  • Evolutionary biology
  • Genetics
  • Molecular evolution

Background:

  • Sex chromosomes are fundamental to sexual reproduction in many species.
  • Their evolution is characterized by remarkable diversity across independent origins.
  • Recent technological advancements have enabled deeper exploration of sex chromosome evolution.

Purpose of the Study:

  • To review theoretical and empirical work on sex chromosome evolution.
  • To highlight key unanswered questions regarding sex chromosome origins and diversity.
  • To discuss recent theoretical progress on the existence of sex chromosomes.

Main Methods:

  • Literature review of theoretical and empirical studies.
  • Analysis of molecular evolution data from diverse organisms.
  • Synthesis of findings on sex chromosome mechanisms.

Main Results:

  • Common evolutionary routes shaping sex chromosomes are increasingly understood.
  • Significant diversity exists in sex chromosome systems, with origins still debated.
  • Pending questions include degeneration, dosage compensation, and gene content evolution.

Conclusions:

  • While common evolutionary patterns are emerging, the drivers of sex chromosome diversity are not fully explained.
  • Further research is needed to address fundamental questions about sex chromosome origins and function.
  • Recent theoretical work offers insights into the evolutionary persistence of sex chromosomes.