Concept explainers
To analyze:
The human melanocortin
Introduction:
The human skin color or pigmentation results from both the parents’ genetic makeup and ultraviolet radiation. The evolution of skin shows the natural selection in order to regulate the penetration of the UV rays into the skin and also controlling its biochemical effects.
Melanin is the pigment that determines the skin color, and it is produced by melanocytes.
The
Eumelanin tends to have black or brown pigmentation, and most often, eumelanin protects skin from UV radiation in sunlight.
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Genetic Analysis: An Integrated Approach (2nd Edition)
- Alzheimer’s is a progressive neurological disorder resulting in dementia and memory loss that occurs in 10% of the US population older than 65. In the 1990s, several researchers showed evidence that the allele of a cholesterol precursor gene, APO E4, increased risk of developing the disorder compared to APO E2 or APO E3. This was especially pronounced if patients carried two alleles of APO E4. However, not all people with APO E4 develop the disorder and some without it will present with Alzheimer's nevertheless. This suggests other genes influence development of the disease. Current research has elucidated dozens of genes that interact with APO E4 pathways in hundreds of ways. As many as 27 of the interactions are epistatic, with some as dominant epistasis and some as recessive epistasis. In addition, some of the gene candidates for non-APO E4 Alzheimer’s have other relationships such as dominant, codominant or incomplete dominant. No reliable cure currently exists for Alzheimer’s…arrow_forwardThe gene SLC24A5 is a key part of the melanin expression pathway, which contributes to skin and hair pigmentation. A SNP that is strongly associated with lighter skin pigment in Europe is rs1426654. The SNP has two alleles, A (darker skin) and G (light skin). fG=100% in Utah European-Americans, 62% in Mexico, 41% in Puerto Rico, 19% African-Americans in Charleston, SC. Calculate FST at this locus. If the genome-wide Fst for humans globally is 0.11, do you think this locus is currently or has been under selection in the past? If so, what type of selection?arrow_forwardWhich of the following best explains how individuals who inherit phenylketonuria alleles can avoid the symptoms of this disease (mental impairment, foul smelling urine)? It exhibits variable expressivity. The expression of this disease depends on the environment. If the individual removes phenylalanine from their diet they can avoid the disease entirely. PKU alleles are epistatic to alleles of another gene, which acts downstream in phenylalanine metabolism. These individuals supplement their diets with enzymes that break-down phenylalanine.arrow_forward
- APOE gene has been found to be a major contributor to sporadic Alzheimer's disease (AD), by acting as an age-of-onset modifier for the common relatively late-onset forms of the disease. Among four alleles causing early onset of AD, the epsilon4 allele (APOE4) disrupts this function. If you generate transgenic monkeys in which the normal allele of APOE gene is knocked out, what phenotype will you expect for those knockout monkeys? A. The APE mRNA expression will be completely suppressed. B. They slow down the development of AD. C. They develop AD early. D. They don't show any AD symptom.arrow_forwardSpherocytosis is an inherited blood disease in which erythrocytes (red blood cells) are spherical instead of biconcave. This condition is inherited in a dominant fashion, with ANK1 (the nonfunctional mutant allele) dominant to ANK1+. In people with spherocytosis, the spleen recognizes the spherical red blood cells as defective and removes them from the bloodstream, leading to anemia; this removal occurs with different efficiency in different people. Some people with spherical erythrocytes suffer severe anemia, some have mild anemia, and others do not have any symptoms of anemia. When 2400 people with the genotype ANK1/ANK1+ were examined, it was found that all of them had spherical erythrocytes, 2250 had anemia of varying severity, and 150 had no anemia symptoms. The ANK1/ANK1 genotype is never observed. Which evidence suggests that spherocytosis is incompletely penetrant?arrow_forwardForward Genetics Analysis uses a variety of beneficial approaches to identify never before described genes. For each of the following approaches or outcomes, briefly (maximum 2 sentences) discuss in your own words, their purpose in Forward Genetics Analysis. c) Mendelian ratios d) Genetic screenarrow_forward
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- Steven Frank and Laurence Hurst argued that a cytoplasmically inherited mutation in humans that has severe effects in males but no effect in females will not be eliminated from a population by natural selection because only females pass on mtDNA (S. A. Frank and L. D. Hurst. 1996. Nature 383:224). Using this argument, explain why males with Leber hereditary optic neuropathy are more severely affected than females.arrow_forwardFor three years, Gunther Schlager and Margaret Dickie estimated theforward and reverse mutation rates for five loci in mice that encodevarious aspects of coat color by examining more than 5 million mice forspontaneous mutations (G. Schlager and M. M. Dickie. 1966. Science151:205–206). They detected the following numbers of mutations at thedilute locus: Gametes examined Mutations detectedForwardmutations 260,675 5Reversemutations 583,360 2 Calculate the forward and reverse mutation rates at this locus. If thesemutations rates are representative of rates in natural populations of mice,what would the expected equilibrium frequency of dilute mutations be?arrow_forwardOne particularly useful feature of the Hardy-Weinberg equation is that it allows us to estimate the frequency of heterozygotes for recessive genetic diseases, assuming that Hardy-Weinberg equilibrium exists. As an example, let’s consider cystic fibrosis, which is a human genetic disease involving a gene that encodes a chloride transporter. Persons with this disorder have an irregularity in salt and water balance. One of the symptoms is thick mucus in the lungs that can contribute to repeated lung infections. In populations of Northern European descent, the frequency of affected individuals is approximately 1 in 2500. Because this is a recessive disorder, affected individuals are homozygotes. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of individuals who are heterozygous carriers?arrow_forward
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