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Related Concept Videos

Epistasis01:39

Epistasis

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...
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Gene Duplication and Divergence

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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.  
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Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
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Human trichromacy revisited.

Hiroshi Horiguchi1, Jonathan Winawer, Robert F Dougherty

  • 1Psychology Department, Stanford University, Stanford, CA 94305, USA.

Proceedings of the National Academy of Sciences of the United States of America
|December 21, 2012
PubMed
Summary
This summary is machine-generated.

Scientists investigated if humans can see light absorbed by melanopsin, a nonvisual photopigment. Results show melanopsin

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Area of Science:

  • Vision science
  • Photobiology
  • Neuroscience

Background:

  • Melanopsin, a photopigment in retinal ganglion cells, is known for nonvisual functions like circadian rhythms.
  • Its role in human visual perception, especially at high light levels, remains unclear.

Purpose of the Study:

  • To determine if light absorbed by melanopsin influences visual perception in healthy humans.
  • To test whether a fourth photopigment class beyond the three cone types is necessary to explain visual sensitivity.

Main Methods:

  • Subjects detected stimuli presented using four independent, intense, and well-controlled light primaries.
  • Detection thresholds were measured in both the fovea and the periphery under high photopic conditions.
  • Data were analyzed to compare observed sensitivity with predictions from trichromatic and tetrachromatic models.

Main Results:

  • Foveal detection thresholds were consistent with standard trichromatic theory (three cone photopigments).
  • Peripheral detection thresholds at high photopic levels deviated from trichromatic predictions.
  • Peripheral sensitivity was better explained by a model incorporating four photopigment classes, including melanopsin.

Conclusions:

  • Melanopsin's light absorption appears to influence visual perception in the human periphery at high light levels.
  • This suggests that melanopsin contributes to visual sensitivity, extending beyond its known nonvisual roles.