Pedigree Analysis

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  The Practical Guide to the Genetic Family History

  • Robin L. Bennett(Author)
  • 2004(Publication Date)
  • Wiley-Liss

    (Publisher)

  A pedigree is a wonderful way to clarify patient misconceptions. Table 1.2 lists many of the common misconceptions patients have about the inheritance of a condition in their family. THE CONTINUING EVOLUTION OF THE PEDIGREE IN THE AGE OF GENOMIC MEDICINE Thanks to the International Human Genome Project, the genes of the human genome are likely to be located and sequenced by the year 2003. The ability to prac- tice genomic medicine, by potentially viewing the molecular status of each patient’s individual genome, has an impact on all medical disciplines. Yet it is absurd to think 10 THE LANGUAGE OF THE PEDIGREE that a complete genomic reference map will then lead us to the understanding of all that is human or that we are the direct and inevitable consequence of our genome. The genetic family history will continue to play an essential role in the medicine of the 21st century. As Dr. Reed Pyeritz (1997), President of the American College of Medical Genetics, succinctly summarizes: The importance of the family history will only be enhanced in the future. Even when an individual’s genome can be displayed on a personal microchip, interpreting that in- formation will depend in large part, on the biological and environmental contexts in which the genome is expressed, and the family milieu is as good a guide as any. Physi- cians can help define those contexts through careful family and social histories. How those histories can be obtained and interpreted, when the average time for patient in- teraction with a physician continues to diminish, are crucial areas for research. Variation is the hallmark of humans—even within well-established diseases with known patterns of inheritance, there is remarkable disease variability. Pedigree as- sessment will continue to play a critical role in our understanding of gene expres- sion.

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  Relative Values

  Reconfiguring Kinship Studies

  • Sarah Franklin, Susan McKinnon, Sarah Franklin, Susan McKinnon(Authors)
  • 2002(Publication Date)
  • Duke University Press Books

    (Publisher)

  Biological scientists are no strangers to familial analyses: from at least Carolus Linnaeus forward, scientific thinkers have used what they understood to be family resemblances to classify, assign taxa, and experiment with the building blocks of life. While the study of inheritance in the classic era mainly involved plant and animal hybrids, modern medical genetics has always de-pended on the pedigree within individual families and the ‘‘family resem-blances’’ across pathological instances to advance diagnoses and interven-tions. Close observation and classification of abnormalities is, of course, a cen-tral strategy in the development of clinical medicine. Normality, as the work of George Canguilhem () and others asserts, is defined in a contras-tive system with abnormality. Tracing family pedigrees and imagining the various routes by which affliction was transmitted among those with rec-ognizable pathologies are two classic methodological strategies for accumu-lating knowledge about diseases and disorders. In the nineteenth century, these closely reasoned characterizations of abnormal people were conven-tionally assigned the name of their medical surveyors, who often drew quite philosophical lessons from their patient populations—for example, Dr. John Down’s famous syndrome was based on his humanist insistence that the ‘‘racial regression’’ involved in ‘‘Mongolism’’ proved the unity of the human species since the parents of the affected were almost always English people of normal intelligence, rather than individuals from a ‘‘lower’’ race (Down  Rayna Rapp, Deborah Heath, & Karen-Sue Taussig , ; compare Gould ).

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  Visualizing Human Biology

  • Kathleen A. Ireland(Author)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  Pedigree Charts Trace Traits Through Families Pedigree charts are symbolic representations of genetic transmission of phenotypic traits through families. Using a pedigree chart like the one shown in Figure 21.8, researchers can trace the pathway of a dis- ease through families, and characteristics of its transmission can be deduced. If, for example, the disease is autosomal dominant, anyone with alleles Aa or AA will be afflicted. If the disease shows up sporadi- cally or appears in a child of two asymptomatic parents, the disease is probably autosomal recessive, and both parents are heterozygous carriers for the dysfunctional allele. FIGURE 21.7 Punnett square for the inheritance of red- green color blindness A cross is shown here between a male with normal color vision and a female who carries the recessive color-blindness allele on one of her X chromosomes. In this Punnett square, the X chromosomes indicated in black font, with an upper case C superscript, carry the normal allele for color vision. The X chromosomes indicated in red font, with a lower case c superscript, carry the defective allele. Y X C X c X C X c X C X C Y X C Y X C X c X C X C X C X c X C Y X c Y X C Y X C X C X C X c X c Y Possible sperm types Possible ova types Punnett square Possible genotypes of zygotes (in boxes) Meiosis Possible phenotypes of offspring Normal male Normal female who carries recessive gene Normal female Normal female (carrier) Normal male Color-blind male geneticist). Figure 21.7 shows an example of a Punnett square used to predict inheritance of a sex-linked trait. Punnett squares predict phenotypic ratios Punnett squares predict the phenotypic ratios that Mendel observed in his pea plant experiments. Crossing a homozygous dominant individual and a homozygous recessive individual yields 100% heterozygous offspring, regardless of the trait. All of the offspring will express the dominant trait.

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  Genetics and Genomics in Medicine

  • Tom Strachan, Anneke Lucassen(Authors)
  • 2022(Publication Date)
  • CRC Press

    (Publisher)

  McKusick (2007) under Further Reading for further details.

  GeneCards® (http://www.genecards.org ). A gene-centered database, this contains a large amount of automatically generated entries, mostly relating to specific human genes. It provides substantial biological information about each gene.

  Investigating family history of disease and recording pedigrees

  The extent to which a human disorder has a genetic basis can often be established by taking a family history. Medical records may be available to health service professionals for some family members; details of deceased family members and others who may be difficult to contact may be obtained by consulting more accessible family members.

  A pedigree is a graphical representation of a family tree that uses the standard symbols depicted in Figure 5.1 . Generations are often labeled with Roman numerals that increase from top to bottom of the page (toward the youngest generation). Individuals within each generation are given Arabic numerals that increase from left to right. An extended family covering many generations may be described as a kindred. A family member through whom the family is first ascertained (brought to the attention of health care professionals) is known as the proband (also called propositus—feminine proposita) and may be marked with an arrow.

  Figure

  5.1

  Pedigree symbols.

  The term sib (sibling) is used to indicate a brother or sister, and a series of brothers and sisters is known as a sibship. According to the number of steps in the pedigree that links two family members, they may be classified relatives of the first degree (parent and child; sibs); second degree (grandparent and grandchild; uncle/aunt and nephew/niece; half-sibs); third degree (first cousins), and so on. Couples who have one or more recent ancestors in common are said to be consanguineous

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  Eugenics, Human Genetics and Human Failings

  The Eugenics Society, its sources and its critics in Britain

  • Pauline Mazumdar(Author)
  • 2005(Publication Date)
  • Routledge

    (Publisher)

  1 They could demonstrate that something was clearly hereditary without implying that it was either a Mendelian unit-character or part of the quantitative spectrum of blended inheritance in the biometric style. Conversely they could be used to demonstrate both of these theories, and even the influence of environment on an inherited constitution. Quite often there was no analysis of the pedigree in terms of any theory of transmission at all: it was the simple fact that like produced like that interested the eugenists. In the period from 1900 to 1930, the period when the Eugenics Society dominated the field, the methodology of human genetics in Britain was in practice the uncommitted pedigree study. In the United States too, the collection of pedigrees was the main method of study. American eugenists standardised and refined the symbolism used, and the British group adopted their conventions. But to the Americans, the pedigree implied a Mendelian interpretation of heredity. Its usefulness lay not only in the straightforward claim that it showed something to be inherited, but also in its ability to distinguish at a glance the dominant and recessive modes of transmission. Skipping a generation at once suggested, or even proved, that a condition was inherited as a Mendelian recessive.

  German eugenists too began work at the turn of the century with a methodology based on the collection of pedigrees. Many years before either the Americans or the British, the German eugenists began to develop the mathematical models of Mendelism that were to supersede scientifically the simple ad oculos demonstrations of the English literature. But though the pedigree had come to the end of its reign in Germany as a scientific tool, it gained a new significance as the official proof of Aryan descent under the race laws of the Nazi racial state.

  It is now often said that Mendelism and biometry represented two distinct and incompatible ways of explaining inheritance and evolution and that they were practised in two different camps by different groups of people who saw themselves as enemies. W.B. Provine has suggested that these camps were kept apart by the personal enmity of their leaders, Karl Pearson of the biometricians and William Bateson of the Mendelians.2

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