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Related Concept Videos

Frequency-dependent Selection01:21

Frequency-dependent Selection

20.2K
When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.
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The Y Chromosome Determines Maleness02:19

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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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Testes: Gross Anatomy01:19

Testes: Gross Anatomy

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The testes, also known as testicles, are the male gonads. They are housed within the scrotum, a sac-like structure located beneath the penis. The scrotum's primary role is to regulate the temperature of the testes, which is crucial for sperm production.
Each testis is surrounded by the tunica albuginea, a dense connective tissue layer that provides structural support and protection. This layer is covered by an outer serous membrane called the tunica vaginalis, which helps reduce friction...
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Testes: Histology01:27

Testes: Histology

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A tough, fibrous membrane, the tunica albuginea, covers the testes, extending inward to form fibrous partitions or septa, dividing them into internal compartments called lobules. Each lobule has 1 to 3 tightly coiled seminiferous tubules where sperm production occurs. These tubules merge into a tubular network at the back of the testis, known as the rete testis. It connects to 15 to 20 efferent ductules, leading to the epididymis.
The spermatogenic cells, responsible for producing sperm, are...
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In-vitro Mutagenesis01:16

In-vitro Mutagenesis

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To learn more about the function of a gene, researchers can observe what happens when the gene is inactivated or “knocked out,” by creating genetically engineered knockout animals. Knockout mice have been particularly useful as models for human diseases such as cancer, Parkinson’s disease, and diabetes.
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Related Experiment Video

Updated: May 6, 2026

Isolate Cell-Type-Specific RNAs from Snap-Frozen Heterogeneous Tissue Samples without Cell Sorting
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Human testis-specific genes are under relaxed negative selection.

Denis Pierron1, Harilanto Razafindrazaka, Christophe Rocher

  • 1Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI, 48201, USA.

Molecular Genetics and Genomics : MGG
|November 9, 2013
PubMed
Summary
This summary is machine-generated.

Negative selection acts on human genes, but is relaxed for testis-specific genes. Deleterious SNPs are less common overall, yet more frequent in genes expressed in the testes, suggesting evolutionary changes in male reproduction.

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Area of Science:

  • Evolutionary genetics
  • Human genomics
  • Molecular biology

Background:

  • Selective pressures on genes vary across organs during human evolution.
  • Understanding organ-specific selection provides insight into evolutionary processes.

Purpose of the Study:

  • To investigate organ-determined negative selection forces.
  • To compare non-synonymous single nucleotide polymorphism (SNP) diversity in genes across different organs.

Main Methods:

  • Utilized the HapMap dataset across 11 human populations.
  • Determined SNP frequencies and predicted the deleteriousness of resulting amino acid changes.
  • Analyzed SNP diversity in genes specific to various organs, including the testes.

Main Results:

  • Deleterious SNPs were found at significantly lower frequencies than tolerated SNPs across all studied organs.
  • Testis-specific genes exhibited a higher proportion of deleterious SNPs compared to genes from other organs.
  • This indicates relaxed negative selection on genes specific to the testes.

Conclusions:

  • Negative selection operates genome-wide but is less stringent on testis-specific genes.
  • Findings support hypotheses of recent evolutionary changes in the human male reproductive system.
  • Organ-specific gene expression influences the efficacy of negative selection.