Unit 3 Part 1 - Chapter 14 (Mendelian Genetics) - DAY 2
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Unit 3 Part 1 - Chapter 14 (Mendelian Genetics) - DAY 2 - Leaderboard
Unit 3 Part 1 - Chapter 14 (Mendelian Genetics) - DAY 2 - Details
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17 questions
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| Why are humans not good subjects for genetic research? | - Generation time is too long - Parents produce relatively few offspring - Breeding experiments are unacceptable However, basic Mendelian genetics endures as the foundation of human genetics In human genetics, geneticists analyze the results of human matings that have already occurred |
| Pedigree | - A pedigree is a family tree that describes the inheritance of a trait across generations - Pedigrees can be used to make predictions about future offspring - We can use the multiplication and addition rules to predict the probability of specific phenotypes |
| Recessively Inherited Disorders | - Many genetic disorders are inherited in a recessive manner - These range from relatively mild to life-threatening - Recessively inherited disorders show up only in individuals homozygous for the allele - Example: Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair |
| Carriers | - Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal - Most individuals with recessive disorders are born to carrier parents - If a recessive allele that causes a disease is rare, it is unlikely that two carriers will meet and mate |
| Consanguineous matings | - Consanguineous matings (that is, between close relatives) increase the chance that both parents of a child carry the same rare allele - Most societies and cultures have laws or taboos against marriages between close relatives |
| Cystic fibrosis | - Cystic fibrosis is the most common lethal genetic disease in the United States, striking one out of every 2,500 people of European descent - The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes, leading to a buildup of chloride ions outside the cell - Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine - Untreated, cystic fibrosis can cause death by the age of 5 - Daily doses of antibiotics to stop infection and physical therapies can prolong life - In the United States, more than half of those with cystic fibrosis now survive into their 40s |
| Sickle-cell disease | - Sickle-cell disease affects one out of 400 African-Americans - It is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells - In homozygous individuals, all hemoglobin is abnormal (sickle-cell) - Symptoms include physical weakness, pain, organ damage, and even paralysis - Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms - About one out of ten African-Americans has sickle-cell trait, an unusually high frequency - Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous in regions where malaria is common |
| Dominantly Inherited Disorders | - Some human disorders are caused by dominant alleles - Dominant alleles that cause a lethal disease are rare and arise by mutation - Example: Achondroplasia is a form of dwarfism caused by a rare dominant allele |
| Huntington’s disease | - Huntington’s disease is a degenerative disease of the nervous system - The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age - Once the deterioration of the nervous system begins, the condition is irreversible and fatal - The timing of onset of a disease significantly affects its inheritance - There is a test that can detect the presence of the Huntington’s allele in an individual’s genome - Some individuals with a family history of Huntington’s disease choose to be tested for the allele - Others decide that it would be too stressful to find out |
| Multifactorial Disorders | - Many diseases, such as heart disease, cancer, alcoholism, and mental illnesses, have both genetic and environmental components - No matter what our genotype, our lifestyle has a tremendous effect on phenotype |
| Genetic Testing and Counseling | - Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease - Fetal and newborn testing can also reveal genetic disorders |
| Genetic Counselor Couple Example (For reference) | - Suppose a couple both have a brother who died from the same recessively inherited disease - A genetic counselor can help determine the risk that this couple will have a child with the disease - It is important to remember that each child represents an independent event in the sense that its genotype is unaffected by the genotypes of older siblings - If both members of the couple had a sibling with the recessively inherited illness, both of their parents were carriers - Thus each has a ⅔ chance of being a carrier themselves - If both are carriers, there is a ¼ chance of each child having the recessive illness - The overall probability of them having a child with the illness is ⅔ × ⅔ × ¼ = 1/9 |
| Tests for Identifying Carriers | - For a growing number of diseases, tests are available that identify carriers and help define the odds of having an affected child more accurately - The tests enable people to make more informed decisions about having children - However, they raise other issues, such as whether affected individuals fully understand their genetic test results, and how the test results are used |
| Amniocentesis | - Fetal Testing - In amniocentesis, the liquid that bathes the fetus is removed and tested for certain genetic disorders |
| Chorionic villus sampling (CVS) | - Fetal Testing - In chorionic villus sampling (CVS), a sample of the placenta is removed and tested |
| Fetal testing techniques | - Amniocentesis - Chorionic villus sampling - Other techniques, such as ultrasound, allow fetal health to be assessed visually in utero |
| Newborn Screening | - Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States - One common test is for phenylketonuria (PKU), a recessively inherited disorder that occurs in one of every 10,000–15,000 births in the United States - The number of conditions that can be tested in newborns is over 100 and ever-increasing |