Concept explainers
HOW DO WE KNOW?
In this chapter, we focused on many extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. Answer the following fundamental questions:
(a) How were early geneticists able to ascertain inheritance patterns that did not fit typical Mendelian ratios?
(b) How did geneticists determine that inheritance of some
(c) How do we know that specific genes are located on the sexdetermining chromosomes rather than on autosomes?
(d) For genes whose expression seems to be tied to the sex of individuals, how do we know whether a gene is X-linked in contrast to exhibiting sex-limited or sex-influenced inheritance?
(e) How was extranuclear inheritance discovered?
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Mastering Genetics with Pearson eText -- Standalone Access Card -- for Essentials of Genetics (9th Edition)
- Pedigree analysis is a fundamental tool for investigating whether or not a trait is following a Mendelian pattern of inheritance. It can also be used to help identify individuals within a family who may be at risk for the trait. Adam and Sarah, a young couple of Eastern European Jewish ancestry, went to a genetic counselor because they were planning a family and wanted to know what their chances were for having a child with a genetic condition. The genetic counselor took a detailed family history from both of them and discovered several traits in their respective families. Sarahs maternal family history is suggestive of an autosomal dominant pattern of cancer predisposition to breast and ovarian cancer because of the young ages at which her mother and grandmother were diagnosed with their cancers. If a mutant allele that predisposed to breast and ovarian cancer was inherited in Sarahs family, she, her sister, and any of her own future children could be at risk for inheriting this mutation. The counselor told her that genetic testing is available that may help determine if this mutant allele is present in her family members. Adams paternal family history has a very strong pattern of early onset heart disease. An autosomal dominant condition known as familial hypercholesterolemia may be responsible for the large number of deaths from heart disease. As with hereditary breast and ovarian cancer, genetic testing is available to see if Adam carries the mutant allele. Testing will give the couple more information about the chances that their children could inherit this mutation. Adam had a first cousin who died from Tay-Sachs disease (TSD), a fatal autosomal recessive condition most commonly found in people of Eastern European Jewish descent. Because TSD is a recessively inherited disorder, both of his cousins parents must have been heterozygous carriers of the mutant allele. If that is the case, Adams father could be a carrier as well. If Adams father carries the mutant TSD allele, it is possible that Adam inherited this mutation. Because Sarah is also of Eastern European Jewish ancestry, she could also be a carrier of the gene, even though no one in her family has been affected with TSD. If Adam and Sarah are both carriers, each of their children would have a 25% chance of being afflicted with TSD. A simple blood test performed on both Sarah and Adam could determine whether they are carriers of this mutation. Would you want to know the results of the cancer, heart disease, and TSD tests if you were Sarah and Adam? Is it their responsibility as potential parents to gather this type of information before they decide to have a child?arrow_forwardPedigree analysis is a fundamental tool for investigating whether or not a trait is following a Mendelian pattern of inheritance. It can also be used to help identify individuals within a family who may be at risk for the trait. Adam and Sarah, a young couple of Eastern European Jewish ancestry, went to a genetic counselor because they were planning a family and wanted to know what their chances were for having a child with a genetic condition. The genetic counselor took a detailed family history from both of them and discovered several traits in their respective families. Sarahs maternal family history is suggestive of an autosomal dominant pattern of cancer predisposition to breast and ovarian cancer because of the young ages at which her mother and grandmother were diagnosed with their cancers. If a mutant allele that predisposed to breast and ovarian cancer was inherited in Sarahs family, she, her sister, and any of her own future children could be at risk for inheriting this mutation. The counselor told her that genetic testing is available that may help determine if this mutant allele is present in her family members. Adams paternal family history has a very strong pattern of early onset heart disease. An autosomal dominant condition known as familial hypercholesterolemia may be responsible for the large number of deaths from heart disease. As with hereditary breast and ovarian cancer, genetic testing is available to see if Adam carries the mutant allele. Testing will give the couple more information about the chances that their children could inherit this mutation. Adam had a first cousin who died from Tay-Sachs disease (TSD), a fatal autosomal recessive condition most commonly found in people of Eastern European Jewish descent. Because TSD is a recessively inherited disorder, both of his cousins parents must have been heterozygous carriers of the mutant allele. If that is the case, Adams father could be a carrier as well. If Adams father carries the mutant TSD allele, it is possible that Adam inherited this mutation. Because Sarah is also of Eastern European Jewish ancestry, she could also be a carrier of the gene, even though no one in her family has been affected with TSD. If Adam and Sarah are both carriers, each of their children would have a 25% chance of being afflicted with TSD. A simple blood test performed on both Sarah and Adam could determine whether they are carriers of this mutation. If Sarah carries the mutant cancer allele and Adam carries the mutant heart disease allele, what is the chance that they would have a child who is free of both diseases? Are these good odds?arrow_forwardWhat is the difference between a Mendelian multifactorial trait and a polygenic multifactorial trait?arrow_forward
- What findings led geneticists to postulate the multiple- factor hypothesis that invoked the idea of additive alleles to explain inheritance patterns?arrow_forwardin own understanding, what is mendelian genetics?arrow_forward. Which part of the pedigree in Figure 2-23 in your opinion best demonstrates Mendel’s first law?arrow_forward
- When Mendel did his experiments, it was the case that the genes for each trait were on separate pairs of homologous chromosomes. For example, the genes for pod color were on one pair of chromosomes and the genes for the seed coat were on a different pair of chromosomes. What if the genes for the two traits were on the same chromosome? (That is, if the gene for pod color was on the same chromosome as the gene for seed coat.) Would Mendel’s 2nd Law still hold? Why or why not?arrow_forwardProvide a proof that a different phenotype can be produced from the same genotype. What are the possible causes for this different expression? How can the different gene interactions be differentiated from each other and from the Mendelian inheritance?arrow_forward. In Figure 2-17, how does the 3:1 ratio in the bottom-lefthand grid differ from the 3:1 ratios obtained by Mendel?arrow_forward
- Consider Mendelian traits versus polygenic traits. What impact do modifications, such as those offered by CRISPR and genetic testing, have on the generational lineage of these traits?Are some traits (e.g., susceptibility to Sickle Cell Anemia) worth removing from our genome? Support your position.arrow_forwardIn Figure 1-6, the students have 1 of 15 different heights,plus there are two height classes (4′11″ and 5′ 0″) forwhich there are no observed students. That is a total of17 height classes. If a single Mendelian gene can account for only two classes of a trait (such as purple orwhite flowers), how many Mendelian genes would beminimally required to explain the observation of 17height classes?arrow_forwardIn the pedigree shown in Figure Q19–14, the first born in each of three generations is the only person affected by a dominant genetically inherited disease, D. your friend concludes that the first child born has a greater chance of inheriting the mutant D allele than do later children.A. According to Mendel’s laws, is this conclusion plausible?B. What is the probability of obtaining this result by chance?arrow_forward
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