Chapter 4 notes for BIOS 2250
Chapter 4 notes for BIOS 2250 Bios 2250
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This 9 page Class Notes was uploaded by hw767714 on Sunday February 21, 2016. The Class Notes belongs to Bios 2250 at Ohio University taught by Dr. Sugiyama in Winter 2016. Since its upload, it has received 13 views. For similar materials see Genetics in Human Society in Biology at Ohio University.
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BIOS 2250 - Genetics in Human Society ____CHAPTER 4 – PEDIGREE ANALYSIS IN HUMAN GENETICS____ Autosome – a chromosome that isn’t a sex chromosome. (Any chromosome that isn’t an X or a Y chromosome.) Although Punnett squares are useful when determining the potential genetics of offspring, they usually aren’t as accurate for humans. We tend to use pedigree maps to study the potential genetics in humans. Proband – the first affected family member who seeks treatment for their genetic disorder through a genetic counselor or doctor. The main focus of the pedigree map. Keys to reading a pedigree map: ▬ The parents of the offspring have a horizontal line directly connecting them. ▬ A vertical line represents the children they produced. ▬ Squares represent the males and circles represent females. ▬ If the person’s shape is filled in, that means that they are affected by the disorder/condition. ▬ Different generations are usually expressed through roman numerals while the individuals in each generation are expressed with regular numbers ▬ Other symbols: There are 6 common patterns of inheritance that you will find on pedigree maps. These include: ▬ Autosomal Recessive – In order to be affected by the disease or condition, you must have received 100% recessive genes. Autosomal recessive disorders are expressed by males and BIOS 2250 - Genetics in Human Society females equally. The offspring of two affected parents will be affected 100% of the time. ▬ Autosomal Dominant – To have an autosomal dominant disease or condition, you must have a dominant gene for it. Only one dominant gene is needed to express the disorder. Males and females are similarly affected. If the affected parent is homozygous (both of their alleles are the same) then 100% of the children will be affected. The phenotype in homozygous individuals is often more severe than the individuals that are heterozygous. ▬ X-linked Dominant – Disorders and conditions that are present when a dominant X chromosome is present. Males who are affected with an X-linked dominant disease or disorder produce 100% affected daughters. As long as you have at least one affected X chromosome, you will express the trait. On average, 2 times as many females are affected than males. ▬ X-linked Recessive –Disorders and conditions that appear when all of the X chromosomes are recessive. Since males only have one X chromosome, they are more commonly affected by X- linked recessive disorders. If their X chromosome is recessive, they don’t have another X chromosome to help. In order for female to be affected, both of her X chromosomes must be recessive. ▬ Y-linked Inheritance – Disorders and conditions that are present when an affected Y chromosome is present. Only present in males. Passed from fathers to sons. All Y-linked traits are always expressed. ▬ Mitochondrial Inheritance – A disorder that is present when affected mitochondria are inherited. Since you get all of your mitochondria from your mother, an affected male cannot pass this disorder onto his offspring. Males and females are equally affected. Pedigree analysis can help to rule out different possibilities of genetic inheritance. Some genetic disorders can have more than one pattern of inheritance, so pedigree analysis can help to find each individual’s family inheritance. Pedigree analysis has two distinct goals. These include: ▬ Determining whether the trait has a dominant or a recessive pattern of inheritance. ▬ Discovering whether the gene is located on the X chromosome, Y chromosome, or on an autosome. BIOS 2250 - Genetics in Human Society Cystic fibrosis is an autosomal recessive trait. It is caused by an abnormal Cl- channel on the plasma membrane. This affects the glands that produce sweat, mucus, and digestive enzymes. ▬ This can cause problems with breathing, pancreas degeneration, an unhealthy increase in appetite, and poor digestion. These factors can lead to a premature death. ▬ The cystic fibrosis gene is located on chromosome 7, so it is autosomal. ▬ Since it is recessive, having one dominant gene and one recessive gene only makes you a carrier of cystic fibrosis. You don’t actually show any symptoms. ▬ About 1/22 in the US white population are carriers of cystic fibrosis. ▬ If both parents are affected with cystic fibrosis, all of their children will be affected as well. Sickle cell anemia is another example of an autosomal recessive trait. Sickle cell anemia is caused by a mutation in the beta globin part of the hemoglobin gene. (Hemoglobin is a molecule in the red blood cells that transports oxygen.) Sickle cell anemia is named as such because of the “sickle” shaped blood cells. ▬ Symptoms of sickle cell anemia usually aren’t present until after the child is 4 months of age. Symptoms include anemia, paleness, rapid heart rate, shortness of breath, and yellowing of the eyes. This can lead to fatigue, kidney problems, joint pain, and death. ▬ If it goes untreated, this disease can be extremely lethal. The sickle shaped cells can easily stack up and form dangerous clots. ▬ There currently is no permanent cure, but some treatments have somewhat helped. These treatments include drinking lots of water, getting pain treatments, getting a bone marrow transplant, and getting blood transfusions. ▬ A carrier of the sickle cell anemia gene has been found to be resistant to malaria. The disease will only be expressed if the individual has all recessive alleles, but carriers (aka the individuals who have one dominant allele and one recessive allele) are still resistant to malaria. Albinism is another autosomal recessive trait. It is caused by a non- functioning allele in the tyrosinase gene. Individuals with albinism are unable to produce the melanin pigment that gives our skin and hair color. ▬ Symptoms include white skin, white hair, problems with vision, pale or sometimes red eyes. (Red eyes don’t always appear, most eyes are gray.) BIOS 2250 - Genetics in Human Society ▬ One in every 10,000 to 70,000 people have albinism. ▬ In some cultures, people mutilate and/or kill individuals with albinism for uses in witchcraft and other similar practices. This happens mostly in East Africa. Marfan syndrome is an autosomal dominant trait. It is caused by a mutated fibrillin that produces defective, weakened connective tissue. An excess of TGF-β accumulates, which further weakens the connective tissue. The most dangerous effect that Marfan syndrome produces is the weakened, enlarged aorta. ▬ Characteristics include being tall, having thin arms and legs, long and thin fingers and toes. ▬ Due to weakened connective tissue, the aorta can enlarge, weaken, and eventually rupture. ▬ There is not a test or cure for Marfan’s syndrome at this time, patients who are believed to have this disorder are monitored closely. Huntington’s disease is an autosomal dominant trait that causes neurological degeneration. It is caused by a toxic protein being produced in the brain. ▬ Some symptoms include personality changes, agitated behavior, involuntary muscle movement, slow or abnormal eye movement, speech issues, and dementia. ▬ The average onset for this disease is around 30-40 years old, but onset can happen much earlier or later in life. Life expectancy for this disease is around 20 years after onset. ▬ There currently isn’t a cure for this disease, but medications can help manage some symptoms more comfortably. Sex-linked inheritance means that the genes responsible for a certain disease or disorder are located on either the X or Y chromosome. Sex- linked diseases or disorders can be X-linked dominant, X-linked recessive, or Y-linked inheritance. Colorblindness is an X-linked recessive disorder that is common in the male population. The most common type of colorblindness is red-green blindness. In this situation, both red and green turn gray. Some forms of muscular dystrophy are X-linked recessive traits. Individuals without muscular dystrophy have normal levels of dystrophin. Dystrophin stabilizes the membranes of the muscle cells during the muscle contractions. Muscular dystrophy is caused by a lack of dystrophin which causes the muscle membranes to be torn apart by the forces generated by muscle contraction. This eventually causes the muscle tissue to die. BIOS 2250 - Genetics in Human Society ▬ Symptoms include muscle degeneration, problems with motor skills, weakness, fragileness, heart problems, and heart failure. Heart failure is usually the final cause of death. ▬ Individuals with this type of muscular dystrophy often only life for about 20 years. These individuals also are usually in a wheelchair by 12 years old. Hemophilia is an X-linked recessive trait which causes problems with blood clotting. The blood of a hemophiliac is unable to clot which causes the individual to be unable to stop bleeding. ▬ Treatments include injecting blood clotting factors and/or blood transfusions. ▬ About one in every 5,000-10,000 males are affected with hemophilia. Hypophosphatemia is an X-linked dominant trait. Symptoms include low phosphates in the blood, growth retardation, fragile bones, and are vitamin-D resistant. Rickets-like symptoms. Most people who are affected cannot walk well. Congenital generalized hypertrichosis is another X-linked dominant trait. Symptoms include extra hair follicles and abundant upper hair. It is called “werewolf syndrome” because of the extra hair. However, this disorder is strictly cosmetic and doesn’t affect heath in any way. Issues related to mitochondrial inheritance are passed down strictly from mother to offspring. Males cannot pass this on to their children. Symptoms usually include fatigue, vision problems, muscle problems, eye movement and vision, brain functioning, etc. These issues are usually adult onset and are often quite mild. Many people with mitochondrial diseases are not aware of having the disease. Since you get all of your mitochondria from your mother, you only have one species of mitochondria in your body. Variations in gene expression include: ▬ Penetrance – this is the probability that a disease will appear when the diseased genotype is present. For example, someone with the breast cancer gene doesn’t always develop breast cancer. ▬ Expressivity – the degree or severness of a given trait. For example, not all individuals with muscular dystrophy have the same severity of symptoms. Distinguishing the different types of inheritance is very important. Autosomal dominant – An affected individual has to have at least one affected allele. This affects males and females the same. If the affected parent is heterozygous, they can still produce unaffected offspring. BIOS 2250 - Genetics in Human Society Autosomal recessive – In order to be affected by an autosomal recessive disorder, you must have 100% recessive genes. Heterozygous carriers will not express the disorder. Males and females are affected equally. Offspring of 2 affected parents will express the disorder 100% of the time. BIOS 2250 - Genetics in Human Society X-linked dominant – Disorders that are present when at least one dominant X chromosome is present. If a male is affected, 100% of his daughters will be affected. X-linked recessive – Disorders that are present when all of the X chromosomes are recessive. Males are more commonly affected since they only have one X chromosome. BIOS 2250 - Genetics in Human Society Y-linked inheritance – Disorders present when an affected Y chromosome is present. These can only be found in males. Mitochondrial inheritance – a disease that is present when and individual has affected mitochondria. Since you get your mitochondria from your mother, all of an affected females children will also be affected. BIOS 2250 - Genetics in Human Society
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