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Why is there such a huge difference in gene expression between the sexes? Uncovering the secret of dosage compensation!
Biologically, sexual differences in various animals and plants are often reflected in significant differences in their genomes and gene expression. In order to reconcile the differences in gene expression caused by the different numbers of sex chromosomes in organisms, organisms have evolved a dosage compensation mechanism. This phenomenon is not limited to one species, but is a mechanism that adapts to the imbalance of gene expression in different genders in multiple evolutionary branches.
Dosage compensation, the process by which gene expression is balanced between the sexes, has profound biological implications.
In humans and many other mammals, female cells randomly silence the transcription of one of the X chromosomes, ensuring the same expression levels as males. In this case, both sexes have the same number of effective X chromosomes in the cell, an important example of balanced gene expression.
Different dose compensation mechanisms
The mechanisms of dosage compensation vary in different species and can be summarized into three main forms: random X chromosome inactivation, twofold transcription of one male X chromosome, and reduced expression of both X chromosomes in intersex individuals. Half.
Random X chromosome inactivation
Random X chromosome inactivation has been observed in mammals such as humans and mice. This process was first discovered by Murray Barr and Ewert Bertram in 1949. They described a structure present in mammalian female cells that came to be known as Barr bodies, which is actually a condensation of extra X chromosomes.
The law of random X inactivation causes each female cell to express only one X chromosome, thus ensuring the balance of gene expression.
Double transcription of one X chromosome
In species such as Drosophila melanogaster, males possess an X chromosome and compensate by tripling the amount of transcripts from this X chromosome. This mechanism was first proposed by H.J. Muller in 1932. Since then, many scientists have verified the existence of this phenomenon in fruit flies.
The expression of the two X chromosomes in intersex individuals is halved
In Caenorhabditis elegans, gene expression on the two X chromosomes of intersex individuals is halved to ensure a balanced sex ratio. During this process, the dosage compensation complex (DCC) assists in completing this change, allowing the expression of the two X chromosomes to be consistent during embryonic development.
Other species-specific methods
In addition to the three main mechanisms mentioned above, some birds, such as chickens (ZZ/ZW system), only selectively silence part of the redundant Z chromosome genes, rather than the entire gene combination, when achieving gene expression balance. This different dosage compensation method causes male chickens to express only part of the genes on the Z chromosome, resulting in incomplete silence.
Dosage compensation mechanisms across species show how organisms adapt to differences between the sexes by regulating gene expression.
Overall, the mechanism of dosage compensation demonstrates how organisms have addressed the challenges posed by differences in gene expression between testicles and ovaries during their evolution. This not only reveals the complexity of biology, but also reflects the important role of natural selection in gene regulation. As the researchers pointed out, the differences in gene expression caused by these mechanisms have far-reaching significance for the survival and reproduction of organisms. Then, further understanding of the differences in gene regulation between different sexes will affect our understanding of genetics and evolutionary biology. What about cognition?
