Mendelian Genetics

3 Key excerpts on "Mendelian Genetics"

• 

  eBook - ePub

  Advanced Molecular Biology

  A Concise Reference

  • Richard Twyman(Author)
  • 2018(Publication Date)
  • Garland Science

    (Publisher)

  Box 1.1 ). Mendel’s principles of inheritance can be summarized as follows.

  (1) The heredity and variation of characters are controlled by factors, now called genes, which occur in pairs. Mendel called these factors Formbildungelementen (form-building elements).

  (2) Contrasting traits are specified by different forms of each gene (different alleles).

  (3) When two dissimilar alleles are present in the same individual (i.e. in a heterozygote), one trait displays dominance over the other: the phenotype associated with one allele (the dominant allele) is expressed at the expense of that of the other (the recessive allele).

  Table 1.1: Definitions of some common terms used in transmission genetics

  Term	Definition
  Allele	Broadly, a variant form of a gene specifying a particular trait. At the molecular level, a sequence variant of a gene (q.v. wild-type allele, mutant allele, polymorphism)
  Character	A biological property of an organism which can be detected or measured
  Character mode	A general type of character, e.g. eye color
  Character trait, trait, variant	A specific type of character, e.g. blue eye color
  Gene	Broadly, a hereditary factor controlling or contributing to the control of a particular character. At the molecular level, a segment of DNA (or RNA in some viruses) which is expressed, i.e. used to synthesize one or more products with particular functions in the cell (q.v. gene, cistron, gene expression)
  (Gene) locus	The position of a gene (or other marker or landmark) on a chromosome or physical or genetic map. A useful term because it allows discussion of genes irrespective of genotype or zygosity
  Genetic	Pertaining to genes. Of characters, heredity and variation arising from the nucleotide sequence of the gene (cf. epigenetic, environmental

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  A Statistical Approach to Genetic Epidemiology

  Concepts and Applications, with an e-Learning Platform

  • Andreas Ziegler, Inke R. König, Friedrich Pahlke(Authors)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  2 Formal Genetics

  In the previous chapter, we described DNA and RNA as carriers of genetic information. However, before these structures were known, and even before chromosomes had been detected, some regularities had been discovered that still form the basis for formal genetics. Hence, in this chapter we will introduce some of these regularities and discuss their consequences.

  In the subsequent sections, we will focus on Gregor Mendel and look at the laws he derived from the observations in his cloister garden (Section 2.1). On the basis of that, we will address the question of how, in general, phenotypes are inherited in families (Section 2.2) and which complications to these general patterns exist (Section 2.3). We will conclude with a description of another regularity that was independently detected by Godfrey Harold Hardy and Wilhelm Weinberg (Section 2.4).

  To facilitate further description of pedigrees and the transmission of genetic factors, we introduce the conventional symbols for displaying pedigrees (Figure 2.1 ). More complex issues are shown in the literature [55]. In this exemplary pedigree, we depict how the affection with a certain disease is transmitted from generation to generation. The index proband is the individual via whom the pedigree has been ascertained. In Figure 2.1 , the index proband is an affected female in generation F 2. She has three offspring. The brother of the index proband has dizygotic twins. Her sister is a carrier of the mutation and has three offspring, but the information on two of these is fairly incomplete with the affection status of both and the gender of one being unknown.

  Fig. 2.1 Conventional symbols for displaying pedigrees.

  2.1 WHAT ARE MENDEL’S LAWS?

  Gregor Mendel was an Augustinian monk living in Brünn, Czech Republic, from 1822 to 1884. After studying natural sciences at the University of Vienna for two years, he performed large-scale cross-breeding experiments in the monastery gardens. Using pea pod plants or seeds, he observed the transmission of easy-to-distinguish traits such as blossom color or seed color. Through this, he developed some basic concepts on genetic information units he called “factors” that still remain valid today. Unfortunately for Mendel, his observations published in 1866 did not receive due attention until they were rediscovered in 1900 by Robert deVries. For detailed information on the history, the interested reader is referred to Ref. [647].

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Handbook Of Forensic Genetics: Biodiversity And Heredity In Civil And Criminal Investigation

  Biodiversity and Heredity in Civil and Criminal Investigation

  • Antonio Amorim, Bruce Budowle(Authors)
  • 2016(Publication Date)
  • WSPC (EUROPE)

    (Publisher)

  CHAPTER 2

  Mendelian Genetics, Modes of Transmission and Genomics

  Antonio Amorim

  Faculty of Sciences ,University of Porto and IPATIMUP / I3S, Porto, Portugal

     

  There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved

  .

  Charles Darwin (1859) “On the Origin of Species by Means of Natural Selection ,” p. 490.

  Perhaps Charles Darwin was exaggerating poetically on the seemingly infinite forms of life but undoubtedly the current and past biodiversity — some, if not most of which was unknown to him and still unknown to us — is prodigious. At the same time, he was publishing his most famous work, another researcher outside the scientific arena, Gregor Mendel, was determining how the distinctive characteristics of living beings are transmitted from parents to offspring. In his words (Mendel, 1866) “[..] so far, no generally applicable law governing the formation and development of hybrids has been successfully formulated”, since “among all the numerous experiments made, not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of the hybrids appear, or to arrange these forms with certainty according to their separate generations, or definitely to ascertain their statistical relations”. He concluded that “to undertake a labor of such far-reaching extent […] appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the history of the evolution of organic forms ” (italics are ours).

  His work and the importance of his results remained unrecognized for far too many years. Yet, still today his role as founder of a new discipline and creator of a formal theory with no parallel in Biology is not properly acknowledged (Rehmeyer, 2010).

  Sign up to read

  Learn more about book