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Genetics Notes Aristotle: Greek philosopher – lived 2300 years ago *believed traits were carried in the blood as pangenes and transported to the reproductive organs -expressions such as blood relative and bloodline come from this idea *proven wrong when the discovery was made that traits for inheritance were found in each cell on chromosomes and had nothing to do with the blood Gregor Mendel – Austrian Monk *worked on the scientific study of heredity in the late 1800’s *unique background in math and physics *applied mathematical background (probability) to reproduction of pea plants *studied 7 traits for many generations *used probability to predict outcome of a cross *hypothesized that each trait is controlled by something called a “factor” – we now call these factors genes *first to use dominant and recessive Mendel’s Laws 1. The Law of Segregation: a pair of factors (alleles) is separated during the formation of gametes (meiosis) 2. The Law of Dominance: One allele shows up in the phenotype while the other is hidden 3. The Law of Independent Assortment: Factors (traits) are distributed to gametes independently (they don’t travel together) P1 Generation: parental generation F1 Generation: first filial generation – offspring from P1 generation F2 Generation: second filial generation – offspring from F1 generation Applied Genetics Biotechnology is the application of biological science to solve practical problems *people have applied genetics to everyday use longer than they have actually understood them -the natives used controlled breeding to develop corn and potatoes from wild plants - the domestication of the dog from wild wolves Selective Breeding: the breeding of animals and plants to produce a desired trait by choosing which animals/plants will be bred to which animals/plants ex. Sheep for wool Cattle for beef Inbreeding: the crossing of organisms with similar genotypes *when you cross two closely related animals, after several generations you will probably have homozygous alleles for the most desired traits *you can also have homozygous alleles for undesired traits Inbreeding can cause problems -may carry a recessive allele that produces harmful traits when homozygous ex. Deafness in dalmations -offspring may be weak or unhealthy ex. Royalty married royalty to keep bloodline pure and passed on recessive trait for hemophilia Outbreeding: crossing of distantly related organisms *may come from different species or more often from different breeds within the same species -in some cases, the cross may result in larger, healthier offspring ex. Mule *when two species are crossed, offspring is almost always sterile because chromosomes don’t match *outbreeding is done in order to cross the best qualities of each species -used to improve cattle *Brahman cattle: resistant to heat and insects *Hereford cattle: high quality beef Polyploidy: cells have more than two sets of chromosomes *rare – almost always lethal in animal cells *desired trait in plant cells -produce double flowers and larger fruit -can be the source of a new species of plant -polyploidy is induced by applying a chemical called colchicine – prevents the cell from dividing after the chromosomes have doubled Genetic Engineering: Modification of genes using biotechnology *combining DNA from genes of different organisms -called recombinant DNA ex. Genetic engineers have transferred specific human genes into bacteria enabling them to produce proteins *applications of genetic engineering -medicine -insulin, antiviral drugs (interferon), human growth hormone, vaccines -gene therapy for hereditary disease -crops, food Ethical Issues Human Genetics Difficult to study patterns of inheritance -humans have few offspring -too many years between generations -most of what we know about human inheritance comes from studying families and inheritance patterns in populations Pedigree: chart that shows how a trait and the alleles that control that trait are inherited in a family Karyotype: photograph that shows an individuals chromosomes -used to determine chromosomal abnormalities *too few or too many chromosomes *abnormal chromosome size or shape -chromosomes are arranged by size from biggest (#1) to smallest (#23) Chromosomal Disorders *mutations can occur spontaneously – in most cases they are not harmful and do not show up in the phenotype -in severe cases, the fetus does not survive -in a few cases, the mutation is able to sustain and the child is born mentally or physically challenged Non-disjunction: the failure of one or more chromosome pairs to separate during meiosis -this can result in monosomy – 1 chromosome per pair instead of 2 or trisomy – 3 chromosomes instead of 2 Examples: Down Syndrome: Trisomy at site #21 -mildly to severely developmentally disabled -almond eyes and enlarged tongue -short, stocky bodies -muscle development and coordination poor -prone to heart defects Klinefelter Syndrome: Trisomy at site #23 -caused by an extra X chromosome in male XXY -sterile -causes feminine characteristics -breast development, feminine body shape -in females – XXX usually sterile and developmentally disabled Turner Syndrome: Monosomy at site #23 -female X instead of XX -normal childhood – normal intelligence -don’t go through puberty – do not reach normal height and fail to develop sexually -sterile Sometimes a person is born with a normal number of chromosomes but the chromosome structure is abnormal. *Inversion *Missing end *Mutation Cri-du-chat syndrome: disorder caused by a defective chromosome -large deletion from chromosome #5 -cri-du-chat means cry of the cat -babies have a cry that sounds like a cat’s meow -extremely small head -seriously developmentally disabled -seldom survive more than 1-2 years Most genetic disorders in humans are caused by single allele mutations Recessive Genetic Disorders *all alleles are passed on even if not expressed – these alleles remain in the gene pool *recessive disorders are not as common as you must have two recessive alleles to exhibit the disorder Tay-Sachs Disease: fatal genetic disorder that results in the inability to break down lipids causing an accumulation of the substance in the brain *as lipids build up in the brain, the individual suffers blindness and seizures *usually causes death within the first months of life *most often found in Ashkenazi Jews in in central Europe -incidence is 100 times greater than among non-Jews Cystic Fibrosis: disorder that results in excessive secretion of thick mucus from the pancreas, lungs and other organs *leads to blockage of digestive tract, congestion of lungs, pneumonia, and other infections *if untreated, individuals die at an early age *current treatments lead to prolonged life *usually found in Caucasians Dominant Allele Disorders Huntington’s Disease: fatal disorder that involves the deterioration of the nervous system – particularly the brain *individuals don’t develop symptoms until late 30’s or early 40’s *by this time, most people have passed it on to their children Achondroplasia: Dwarfism *never reach more than 4 ft. 4 inches *arms and legs are disproportionately short Other characteristics caused by dominant allele: *polydactyly (extra fingers and toes) *dimples, freckles, widows peaks, ability to roll tongue **A dominant allele disorder is not always more common than a recessive allele disorder X-Linked Traits (sex linked) 1. Colorblindness – can’t distinguish between certain colors 2. Hemophilia – occurs almost exclusively in males -blood can’t clot 3. Duchenne Muscular Dystrophy – progressively weakens and destroys muscle tissue Co-Dominant Allele Disorders Sickle Cell Anemia: abnormal form of hemoglobin – the protein in red blood cells that carries oxygen *sickle cell is co-dominant to normal allele *individuals affected by this disease contain a mixture of normal hemoglobin and sickle cell hemoglobin *sickle cell attack begins when oxygen supply becomes low – sickle cells start to stick together and become tangled masses *clogs capillaries and stop blood flow *extremely painful and can cause death *primarily found in Africans and African-Americans *often found in areas where malaria is common – individuals with sickle cell have an increased resistance to malaria