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Biology 30 – Ch. 27 Applied Genetics Notes Albinism Albinism results from inheritance of rare recessive alleles. The condition is known to affect mammals (including humans), fish, birds, reptiles and amphibians. Characterized by a partial or total lack of _______________________ in the eyes, skin and hair (or more rarely the eyes alone). About 1 in 17,000 human beings has some type of albinism, although up to 1 in 70 is a carrier of albinism genes Most forms of albinism are the result of the inheritance of recessive alleles (genes) passed from both parents of an individual, though some rare forms are inherited from only one parent. The eyes of an animal with albinism occasionally appear red due to the underlying retinal blood vessels showing through where there is not enough pigment to cover them. In humans this is rarely the case, as a human eye is quite large and thus produces enough pigment to lend opacity to the eye, often colouring the iris pale blue. Animals that are albino often are hypersensitive to light due to lack of pigment in the eyes and are extremely susceptible to sunburn and over exposure due to the lack of melanin in their skin Misconceptions A common misconception is that albinos are ____________; they are in fact fully capable of _______________________. It is also thought by many that people with albinism live short life spans. This is not true in general, but may be a distorted view of a more reasonable fact that people with albinism have a higher risk of skin cancer if they do not use proper skin protection when in the sun. It has also been misunderstood that a person or other animal with albinism will become blind halfway through life; this is incorrect. Genetic Disorders and Gene Therapy Chromosomal Diseases Gametes have __________________________________________________ Offspring inherit _____________________________________ a chromosome Caused by problems with _______________________________ Nondisjunction 'Nondisjunction' is the failure of chromosome pairs to _________________________ ___________________________________________ This could arise from a failure of homologous chromosomes to _________________, or the failure ___________________ to separate during _____________________. The result of this error is a cell with an __________________________. When a single chromosome is lost (2n-1), it is called a _____________, in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs. When a chromosome is gained, it is called ______________, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs. 1 Biology 30 – Ch. 27 Applied Genetics Notes Amniocentesis Used on pregnant women over __________ years of age Performed during weeks 15-17 of pregnancy A needle is inserted into the ____________________ Amniotic fluid with _____________ is removed A _______________ (genetic profile) of the fetal chromosomes is prepared . Huntington Disease • Person gradually loses psychomotor control in adulthood • Caused by ____________________ allele Genetics Problem A woman (hh) with normal nerve physiology has a child with a man (Hh) who will develop Huntington Disease. What is the chance that the child will have Huntington Disease? Cystic Fibrosis As of 2002, the median age of survival of Canadians with cystic fibrosis is 37 years of age. Since 1989 when Canadian researchers discovered the gene responsible for CF, global research to find a cure for the disease has brought us closer and closer to a solution. The pace of CF science suggests that there is good reason to feel optimistic about the future. Genetics Problem A woman (Nn) with normal lung physiology has a child with a man (Nn) who has normal lung physiology (both are carriers of allele)n What is the chance that the child will have Cystic Fibrosis? 2 Biology 30 – Ch. 27 Applied Genetics Notes Sickle Cell Disease (Sickle Cell Anemia) • Red blood cells are sickle shaped, interfering with circulatory system and causing anemia and pain. • Caused by a recessive allele Tay Sach’s Disease Tay-Sachs disease is an _____________________ inherited disorder, meaning a child inherits one copy of the abnormal gene from each parent. The parents do not actually have the disease, but carry the Tay-Sachs gene and passes it on to the baby. Infants usually begin to show signs of the disease between 3 months and 6 months of age. Children with Tay-Sachs disease can become deaf, blind and paralyzed, and usually die by the age of 5. Early signs and symptoms can include: Loss of muscle tone, exaggerated response to sudden noises, lack of energy, loss of motor skills, such as the ability to roll over, crawl, reach for things or sit up. Trisomy-21: Down’s Syndrome 1 in 600 births, short, broad nose, epicanthal fold, small oral cavity, large, furrowed tongue, large, irregular teeth, IQs from 20 to 50 Trisomy 13: Patau’s Syndrome 1 in 20,000 births, sloping forehead, small head & eyes, cleft lip and/or palate, heart defects, 75% die in first year, 100% by age 6. Trisomy 18: Edwards’ Syndrome 1 in 11,000 births, small mouth and/or jaw, low-set/malformed ears, clenched fist, index finger overlapping 3rd and 4th fingers, rocker-bottom feet, heart defects, hearing loss, 90% die by age 1. Kleinfelter’s Syndrome 1 in 500 males (XXY), taller than average, partial breast development, small testicles, high-pitched voice, female hair distribution, altered body proportions, hips slightly larger than normal, IQ about 90 Turner’s Syndrome (X) 1 in 2500 females, grow slowly, shield chest when young, low hair line, widely spaced nipples, fail to menstruate, no ova, normal IQ; weakness in math, spatial perception Jacob’s Syndrome (XYY) “Super Male”, 1 in 1000 males, 1 in 50 in prison populations, excessively tall (2/3’s > 6 feet), IQs around 80, low threshold for control of aggression X-Polysomy (XXX, XXXX) XXX, 1 in 1400 females Cannot be distinguished from XX females Problems with spontaneous abortions XXX have normal IQs, increasing numbers cause mental deficiency 3 Biology 30 – Ch. 27 Applied Genetics Notes Genetics & Human Diseases About 4,000 human diseases are thought to be inherited. Scientists are making good progress figuring out where genes are located on chromosomes and in understanding how the mutations in genes cause disease Genetic Testing Now have DNA tests for 30 - 40 diseases • Cystic fibrosis, some forms of breast cancer, fragile X syndrome, Huntington disease, Duchenne muscular dystrophy Tests are up to 99% accurate Tests can be run on embryos created by in-vitro fertilization prior to implantation Future of Genetic Testing Genetic tests for 1000s of genetic diseases will be available after the Proteome Project is completed…or after scientists figure out which proteins go with which genes…probably in 10-20 years. Issues about Genetic Testing What if the news is bad? Should the fetus be aborted or allowed to live with a “cruel” disease? Should insurance coverage provide care for a child having a genetic disease that was diagnosed before birth? Should blood relatives be warned? Should our genetics be part of our records? Should employers be allowed to consider genetically based diseases in hiring employees? Will eugenics (manipulation of the hereditary qualities of a race) be practiced? Gene Therapy Gene therapy is lagging behind genetic testing • For example, gene for cystic fibrosis was identified in 1989 • Scientists have been testing ways to insert copies of the normal gene into cells of the respiratory tract It is difficult to get the gene inserted into the tissue so that it can take over control of protein synthesis Breeding Methods Selection: The process of _______________________________________. Inbreeding: The mating of ________________________individuals to obtain desirable traits. Very common in self fertilizing plants. Hybridization: Crossing individuals that are not closely related to introduce new, beneficial alleles to the population. New individuals are generally hardier than either parent. This is called ________________________. Mutations In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. 4 Biology 30 – Ch. 27 Applied Genetics Notes Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens or viruses Mutations create ________________________________________________. Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes. Peppered Moth The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light coloration, which effectively camouflaged them against the light-colored trees and lichens which they rested upon. However, due to widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees which peppered moths rested on became blackened by soot, causing most of the light-colored moths to die off due to predation. At the same time, the dark-colored moths, flourished because of their ability to hide on the darkened trees. This changing of color of a species due to pollution is called ____________________. 5