Essential Elements of Biochemistry BCHM 3050 Dr Srikripa Chandrasekaran Lecture 3 27 15 Notes Case Study I Evidence that points to a particular gene that is responsible for skin color in humans II Darwin brought about the theory of natural selection o Theory that human intelligence is an inherited trait affected by natural selection III Eugenics Movement Darwin o 1883 coined in England by Sir Francis Galton a cousin of Charles o Greek word meaning well born or of good origins or breeding o Science of improving qualities of race IV The Triangle of life Environment education heritage V Historical case women was diagnosed with feeble mindedness IQ of 56 and was sterilized so that she could not have any more kids and pass on the traits of feeble mindedness o This is a failure in the field of science VI What affects skin color o Close to the equator skin color is darker o Far away from the equator skin color is lighter VII Migration of our ancestors out of Africa first establishment of civilization VIII The yin and yang of radiations o Vitamin D production proportional to light penetration o Folic acid Vitamin B9 destruction proportional to light penetration Too much radiation destroys folic acid Expecting mothers need folic acid to allow for development of spinal chord and maxillary features in child without folic acid child my die In order for the people of Africa to adapt and not lose too much folic acid they had extremely dark skin because of the harsh sunlight allows them to not absorb as much sunlight and maintain folic acid levels o Closer to the equator has more exposure to high amount of UV radiation o UV radiation causes cross links and damages in DNA o The darker the skin do not absorb as much UV radiation IX Special cells called melanocytes make melanin o More melanocytes more melanin o When people with dark skin moved away from harsh sunlight they could not absorb the little bit of sunlight needed to aid them with melanin 1 X Sun Saharan Africans adapted to have darker skin color o Mutation in MC1R a gene responsible for melanin production allowed positive selection for dark skin in early sub Saharan Africans about 130 000 years ago o When we evolved from monkeys lost hair and had light pink skin so we needed to adapted to obtained dark skin color XI Adaptation permitting light skin color o Many genes control melanin levels o Vitamin D UV light makes Vitamin D o Folic Acid Vitamin B9 UV light destroys vitamin B9 o Lots of sunlight Africa increased melanin o Cold less sunlight N Europe less melanin XII Gold fish have smaller fewer more translucent melanocytes o How was the gene responsible for the golden phenotype identified Positional cloning identify where a particular gene is cloning all genes until I locate the position of the gene of interest Slc24a5 is the gene responsible for golden color o Knock down using morpholinos Morpholinos prevent mRNA from being expressed Used in reverse genetics morpholinos are synthetic oligonucleotides which can bind RNA sequences thereby blocking translation Synthetic RNA molecule which is designed to bind to RNA to prevent it from getting translated Prevent mRNA from getting translated Knockdown of slc24a5 with morpholinos in wildtype larvae phenocopies the golden mutation Wild type fish without mutations Golden larvae lack melanin pigments Wild type larvae injected with slc24a5 morpholinos wild type larvae started looking like golden larvae o RNA in situ hydridization to detect RNA in zebrafish larvae Send a color that attached to the RNA of interest Add digoxigenin labeled probe into cell and it attached to mRNA send another enzyme to make it glow able to locate where the mRNA is now because it is colored Wildtype fish could pick up the dye color but the golden fish couldn t because they lacked the gene needed for the color to bind to Sent probe to seek out a gene but it was not present in the mutant showed scientists to determine that that gene was responsible for melanin production o How is this study relevant to human populations 2 Homology studies indicated that the human slc24a5 gene also is an ion transporter Search human gene pool for a similar gene and found that humans have the same gene African decent Ala 111 on slc24a5 gene European Thr 111 on slc24a5 gene Within this gene only a single SNP exists where the nucleotide Allele of slc24a5 with the nucleotide G codes for Alanine at Allele of slc24a5 with nucleotide A codes for Threonine at G is converted to A position 111 position 111 Dark skin a G from mom and dad Intermediate skin color G from one parent and A from another Light skin A from mom and dad Skin color does not make you a fast runner 3
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