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02:32Position-effect Variegation
In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
01:11Genetic Lingo
Overview
01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
01:39Epistasis
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...
01:43Incomplete Dominance
Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.
01:24Color Vision
Color perception begins in the retina, the light-sensitive layer at the back of the eye. Two main theories explain how colors are seen: the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, suggests that color vision is based on three types of cone receptors in the retina. These cones are sensitive to different but overlapping ranges of wavelengths corresponding to red, blue, and green.
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Heterochromia.
1Department of Internal Medicine, Regina General Hospital, Regina Qu'Appelle Health Region, Regina, Sask.
Summary
Congenital Horner syndrome can cause different eye colors and a constricted pupil (miosis) in one eye. This case highlights the varied presentation and clinical significance of this rare condition.
Area of Science:
- Ophthalmology
- Pediatrics
- Genetics
Background:
- Congenital Horner syndrome is a rare condition resulting from damage to the sympathetic nerve pathway to the face and eye.
- It can manifest with a range of symptoms, including miosis, ptosis, and heterochromia iridum.
Observation:
- A patient presented with distinct eye colors (heterochromia iridum) and a constricted pupil (miosis) in the left eye.
- These clinical signs were indicative of an underlying neurological condition.
Findings:
- The patient was diagnosed with congenital Horner syndrome.
- The case underscores the importance of recognizing ocular manifestations of neurological disorders.
Implications:
- Understanding the determinants of eye color in Horner syndrome is crucial for diagnosis and management.
- This case contributes to the clinical understanding of congenital Horner syndrome's presentation and potential long-term effects.