Finding a Target
Nathan Keighley in Miraculous Medicines and the Chemistry of Drug Design, 2020
Different sequences of these base pairs comprise a gene. Genes are the information containing elements of DNA that code for a particular protein and produce hereditary characteristics, such as eye colour. In a population, there may be different forms of the same gene. In the example of eye colour, the gene coding for the pigment in the iris varies between people who have different coloured eyes. The different forms of a gene are called alleles. Remarkable diversity of proteins is achieved from these four bases. The unique sequence of the bases on a gene governs the specific sequence of amino acids during protein synthesis. The DNA sequence exhibits a triplet code, where a particular combination of three base pairs codes for a particular amino acid when translated from the RNA sequence at the ribosome, which was transcribed from DNA. A particular sequence of triplets codes for a specific protein.
Cancer Biology and Genetics for Non-Biologists
Trevor F. Cox in Medical Statistics for Cancer Studies, 2022
A gene can have different codings, and these variants are called alleles. One allele is inherited from your mother and one from your father for each gene, and these determine your physical traits (phenotype), such as hair colour, height, etc. The combination of the alleles that you have inherited make up your genotype, but we can also use this term for a particular gene. If there are two possible alleles for a gene, A and a, there are three possible genotypes, AA, Aa and aa, depending on which alleles you inherited. For example, the OCA2 gene on chromosome 15 is associated with melanin production, which is a pigment for hair, eye and skin colour. A might be the allele for brown eyes and a for blue eyes. A is dominant and a is recessive, and so individuals with AA and Aa will have brown eyes, and individuals with aa will have blue eyes. But eye colour is not quite so simple as this as other genes are also involved. The allele that codes for the most common phenotype is called the wild type allele.
Genetic Principles
Gail S. Anderson in Biological Influences on Criminal Behavior, 2019
The X and Y chromosomes not only determine sex but also carry other genes. The X chromosome is quite large and carries many genes, but the Y chromosome is very small and carries only a few genes. If a gene is on a sex chromosome, it is said to be sex linked. Usually, this means that it is on the X chromosome, simply because it has more genes. We know about a few such sex-linked genes, and some cause diseases in humans. We know the most about genes that cause diseases, because they are of most interest to us. Genes that are involved in hair or eye color are not so vital and therefore do not get the same research attention. Two classic examples of sex-linked conditions are color blindness and hemophilia.2 They are both usually found in men and only very rarely in women. It is quite common for men to be color blind but not for women, and the same is true for hemophilia. The reason is that both diseases are caused by recessive genes. The dominant form is normal. If you think back about the earlier examples relating to dominant and recessive genes, you will see that people only express the recessive gene if they have two recessive alleles. If they had two dominant alleles, or one of each, then the recessive gene would not be expressed, just as the purple flower “hid” the white flower. Also, these disease-causing recessive genes are usually fairly rare, so the allele ratio may be 98% normal dominant and 2% disease-causing recessive.
Natural options for management of melasma, a review
Published in Journal of Cosmetic and Laser Therapy, 2018
Mpofana N, Abrahamse H
A blemish free, even skin tone is desirable by everybody. Flawless skin is considered a universal indication of beauty and healthy skin (1). Melanin, a naturally occurring pigment in humans, is responsible for skin, hair, and eye color, therefore determines our race and phenotypic appearance (2). It plays a vital protection role from cytotoxic ultraviolet (UV) radiation and oxidative stress (3,4). Melanin is produced from the melanosomes and transferred from melanocytes to keratinocytes (2,5,6). Melanin production is controlled by the expression and activity of a copper containing enzyme, tyrosinase (7). Tyrosinase is a vital enzyme involved in melanin synthesis. Tyrosinase regulates the catalytic processes of hydrolysis of tyrosine to l-DOPA as well as oxidation of DOPA to DOPA quinine (2,7–9). When this process is malfunctioning, it often leads to overproduction of melanin. Over secretion of melanin causes unwanted skin problems such as post-inflammatory melanoderma, hyperpigmentation, and melasma (4).
Faces: Identification and Biases
Published in Issues in Mental Health Nursing, 2020
Jacquelyn H. Flaskerud
Researchers in the psychology of eyewitness identification say that it is not bias or bigotry that makes it difficult for people to distinguish between people of another race. It is the lack of early and meaningful exposure to other groups that often makes it easier for us to quickly identify and remember people of our own ethnicity or race while we often struggle to do the same for others (Malpass, Ross, Meissner & Marcon, 2009). Starting when we are infants and young children, people become attuned to the key facial features and characteristics of those around them. Whites often become accustomed to focusing on differences in hair color and eye color. African-Americans grow more familiar with subtle shadings of skin color. It is a product of our perceptual experience. Minorities tend to be better at cross-race identification than whites in part because they have more extensive and meaningful exposure to whites than the other way around (Malpass et al., 2009). However, a meta-analysis of 30 years of research has shown that interracial contact accounts for only about 2% of the variance in own race bias across samples. Although negative racial attitudes are correlated with limited interracial contact, no relationship has been found between the ORB and racial attitudes, whether explicit or implicit (Johnson & Fredrickson, 2005).
The Invention of Heterosexual Culture, by Louis-Georges Tin
Published in Journal of Homosexuality, 2018
Michael Ferguson
The presence of romantic love and passionate heterosexual connection in antiquity—or at any time—should not be surprising. Men and women do enjoy having sex together—sometimes. But the prevailing social ethos was homoerotic. This is the point that Tin makes. It is not that heterosexuality did not exist in premodern societies or that some people did not prefer it and find satisfaction in it or even idealize it. The point is that the culture, the prevailing attitudes, values, and expectations, did not hold it in high regard and in many quarters were contemptuous of it. Ancient societies did not think in the dichotomies characterizing sex that we are trapped in today. We need to keep in mind that the word heterosexuality—and thus the concept—did not appear in the English language until the late 19th century (Tin, p. 157). In fact, heterosexual and homosexual are artificial constructions that have come into the language only a little over 100 years ago. They are not inherent qualities of people such as hair and eye color. As Christianity recedes and sexuality becomes looser and more flexible, the need to categorize people by who they have sex with will diminish, and we will be able to abandon these terms altogether.
Related Knowledge Centers
- Eye
- Phenotypic Trait
- Polygene
- Turbidity
- Melanin
- Iris
- Scattering
- Stroma of Iris
- Iris Pigment Epithelium
- Tyndall Effect