Biological Sciences
Chromosomal Theory of Inheritance
The Chromosomal Theory of Inheritance states that genes are located on chromosomes and that the behavior of chromosomes during meiosis and fertilization accounts for Mendelian inheritance patterns. This theory, proposed by Walter Sutton and Theodor Boveri in the early 20th century, provided a unifying explanation for the inheritance of traits and laid the foundation for modern genetics.
Written by Perlego with AI-assistance
Related key terms
1 of 5
10 Key excerpts on "Chromosomal Theory of Inheritance"
eBook - PDF- Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
13 | MODERN UNDERSTANDINGS OF INHERITANCE Figure 13.1 Chromosomes are threadlike nuclear structures consisting of DNA and proteins that serve as the repositories for genetic information. The chromosomes depicted here were isolated from a fruit fly’s salivary gland, stained with dye, and visualized under a microscope. Akin to miniature bar codes, chromosomes absorb different dyes to produce characteristic banding patterns, which allows for their routine identification. (credit: modification of work by “LPLT”/Wikimedia Commons; scale-bar data from Matt Russell) Chapter Outline 13.1: Chromosomal Theory and Genetic Linkage 13.2: Chromosomal Basis of Inherited Disorders Introduction The gene is the physical unit of inheritance, and genes are arranged in a linear order on chromosomes. Chromosome behavior and interaction during meiosis explain, at a cellular level, inheritance patterns that we observe in populations. Genetic disorders involving alterations in chromosome number or structure may have dramatic effects and can prevent a fertilized egg from developing. Chapter 13 | Modern Understandings of Inheritance 361 13.1 | Chromosomal Theory and Genetic Linkage By the end of this section, you will be able to do the following: • Discuss Sutton’s Chromosomal Theory of Inheritance • Describe genetic linkage • Explain the process of homologous recombination, or crossing over • Describe chromosome creation • Calculate the distances between three genes on a chromosome using a three-point test cross Long before scientists visualized chromosomes under a microscope, the father of modern genetics, Gregor Mendel, began studying heredity in 1843. With improved microscopic techniques during the late 1800s, cell biologists could stain and visualize subcellular structures with dyes and observe their actions during cell division and meiosis.
eBook - PDF- Julianne Zedalis, John Eggebrecht(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
These questions address the following standards: [APLO 3.2][APLO 3.11][APLO 3.14][APLO 3.15][APLO 3.28][APLO 3.26][APLO 3.17][APLO 4.22] Long before chromosomes were visualized under a microscope, the father of modern genetics, Gregor Mendel, began studying heredity in 1843. With the improvement of microscopic techniques during the late 1800s, cell biologists could stain and visualize subcellular structures with dyes and observe their actions during cell division and meiosis. With each mitotic division, chromosomes replicated, condensed from an amorphous (no constant shape) nuclear mass into distinct X-shaped bodies (pairs of identical sister chromatids), and migrated to separate cellular poles. 518 Chapter 13 | Modern Understandings of Inheritance This OpenStax book is available for free at http://cnx.org/content/col12078/1.6 Chromosomal Theory of Inheritance The speculation that chromosomes might be the key to understanding heredity led several scientists to examine Mendel’s publications and re-evaluate his model in terms of the behavior of chromosomes during mitosis and meiosis. In 1902, Theodor Boveri observed that proper embryonic development of sea urchins does not occur unless chromosomes are present. That same year, Walter Sutton observed the separation of chromosomes into daughter cells during meiosis (Figure 13.2). Together, these observations led to the development of the Chromosomal Theory of Inheritance, which identified chromosomes as the genetic material responsible for Mendelian inheritance. Figure 13.2 (a) Walter Sutton and (b) Theodor Boveri are credited with developing the Chromosomal Theory of Inheritance, which states that chromosomes carry the unit of heredity (genes). The Chromosomal Theory of Inheritance was consistent with Mendel’s laws and was supported by the following observations: • During meiosis, homologous chromosome pairs migrate as discrete structures that are independent of other chromosome pairs.
eBook - PDF- D. Peter Snustad, Michael J. Simmons(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
This idea, called the Chromosome Theory of Heredity, stands as one of the most important achievements in biology. Since its formulation in the early part of the twentieth century, the Chromosome Theory of Heredity has provided a unifying framework for all studies of inheritance. Sperm White-eyed female Normal eggs Nondisjunctional eggs X X X w w XX red-eyed female w + w w w Red-eyed male X Y w + XXX metafemale (usually dies) XO exceptional red-eyed male YO (dies) P F 1 nullo-X XY white-eyed male XXY exceptional white-eyed female w w w + w w w w w + w + ◾ FIGURE 5.5 X chromosome nondisjunction is responsible for the exceptional progeny that appeared in Bridges’ experiment. Non- disjunctional eggs that contain either two X chromosomes or no X chromosome unite with normal sperm that contain either an X chromo- some or a Y chromosome to produce four types of zygotes. The XXY zygotes develop into white-eyed females, the XO zygotes develop into red-eyed, sterile males, and the YO zygotes die. Some of the XXX zygotes develop into sickly, red-eyed females, but most of them die. The Chromosome Theory of Heredity 93 94 Chapter 5 The Chromosomal Basis of Mendelism THE CHROMOSOMAL BASIS OF MENDEL’S PRINCIPLES OF SEGREGATION AND INDEPENDENT ASSORTMENT Mendel established two principles of genetic transmission: (1) the alleles of a single gene segregate from each other, and (2) the alleles of two different genes assort independently. The finding that genes are located on chromosomes made it possible to explain these principles (as well as exceptions to them) in terms of the meiotic behavior of chromosomes. The Principle of Segregation During the first meiotic division, homologous chromosomes pair. One of the homologues comes from the mother, the other from the father. If the mother was homozygous for an allele, A, of a gene on this chromosome, and the father was homo- zygous for a different allele, a, of the same gene, the offspring must be heterozygous, that is, Aa.
eBook - ePub- Dov M. Gabbay, Paul Thagard, John Woods(Authors)
- 2007(Publication Date)
- North Holland(Publisher)
For Morgan the Chromosomal Theory of Inheritance provided the resolution to the phenomenon of deviation from independent segregation of trait, or linkage [ Morgan, 1911 ]. I venture to suggest a comparatively simple explanation based on results of inheritance of eye color, body color, wing mutations and the sex factor for femaleness in Drosophila. If the materials that represent these factors are contained in the chromosomes, and if those factors that “couple” be near together in a linear series, then when the parental pairs (in the heterozygote) conjugate like regions will stand opposed. … [W]hen the chromosomes separate (split) … the original material will, for short distances, be more likely to fall on the same side of the split, while remoter regions will be as likely to fall on the same side as the last, as on the opposite side. … [W]e find coupling in certain characters, and little or no evidence at all of coupling in other characters; the difference depending on the linear distance apart of the chromosomal materials that represent the factors. … The results are a simple mechanical result of the location of the materials in the chromosomes, … and the proportions that result are not so much the expression of a numerical system as of the relative location of the factors in the chromosomes. [ Morgan, 1911 ] For the Chromosomal Theory of Inheritance to be the explanation of linkage, it was necessary to spell out why linkage was not absolute, or, why all factors linked to a given chromosome should not segregate as a unit. Since “coupling” and “repulsion” were not absolute, Morgan had to add the notion of crossing over, which he borrowed from Janssens’ chiasmatype theory, based on observations of meiosis at spermatogenesis in the Batarchine salamander [ Janssens, 1909 ]. During meiosis homologous chromosomes (each had already replicated to form two chromatids) pair, and are increasingly coiled and twisted one about the other up to the pachytene stage
eBook - ePubBiology Trending
A Contemporary Issues Approach
- Eli Minkoff, Jennifer K. Hood-DeGrenier(Authors)
- 2023(Publication Date)
- CRC Press(Publisher)
CHAPTER 2 Genes, Chromosomes, and DNADOI: 10.1201/9781003391159-2CHAPTER OUTLINE
- MENDEL OBSERVED PHENOTYPES AND FORMED HYPOTHESES
- THE CHROMOSOMAL BASIS OF INHERITANCE EXPLAINS MENDEL'S HYPOTHESES
- OUR UNDERSTANDING OF DNA FURTHER EXPLAINS MENDEL'S HYPOTHESES
- CONCLUDING REMARKS
- CHAPTER SUMMARY
- BIBLIOGRAPHIC REFERENCES
ISSUES- How have our concepts of genes developed?
- What are the limitations of Mendelian genetics?
- Does Mendelian genetics explain inheritance in all species?
- How is hereditary material copied?
BIOLOGICAL CONCEPTS- The gene
- Patterns of inheritance
- Mitosis and meiosis
- DNA (the genetic material, DNA structure, DNA replication)
How do offspring come to resemble their parents physically? This is the major question posed by the field of biology called genetics, the study of inherited traits. Genetics begins with the unifying assumption that biological inheritance is transmitted by structures called genes. The discovery of what genes are and how they work has been the subject of many years of research. Among the earliest findings was the fact that the same basic patterns of inheritance apply to most organisms. The inheritance of many human traits can be explained by the same hypotheses first formulated from the study of pea plants. These basic principles are discussed in this chapter. The inheritance of other human traits, such as sex determination and susceptibility for many diseases, involves further complications that are addressed in Chapter 3 .We now know that genes are made of DNA, and we will discuss how we know this later in the chapter. We begin, however, with experimental evidence for the existence of genes and their role in inheritance.2.1 MENDEL OBSERVED PHENOTYPES AND FORMED HYPOTHESES
No two individual organisms are exactly alike. Folk wisdom going back to ancient times taught people that a child or an animal resembles both its mother and its father by showing a mixture of traits derived from the two sides of the family. This suggested a concept that came to be called “blending inheritance,” in which heredity was compared to a mixing of fluids, often identified as “blood.” The research we are about to describe caused this explanation to be abandoned.
eBook - PDFHuman Heredity
Principles and Issues
- Michael Cummings(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
© Cengage Learning Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 3-6 Meiosis Explains Mendel’s Results: Genes Are on Chromosomes | 53 many different organisms, it became obvious that genes and chromosomes had much in common ( Table 3.2 ). Both chromosomes and genes occur in pairs. In meiosis, members of a chromosome pair separate from each other, and members of a gene pair separate from each other during gamete formation ( Figure 3.10 ). Finally, the fusion of gametes during fertilization restores the diploid number of chromosomes and two copies of each gene to the zygote, producing the genotypes of the next generation. In 1903, Walter Sutton and Theodor Boveri independently proposed that because genes and chromosomes behave in similar ways, genes must be located on chromosomes. This idea, the chromosome theory of inheritance, has been confirmed in many different ways and is one of the foundations of modern genetics. Each gene is located at a specific site—called a locus —on a chromosome, and each chromosome carries many genes. In humans, it is estimated that 20,000 genes are carried on the 24 different chromosomes (22 autosomes, the X, and the Y). Locus The position occupied by a gene on a chromosome.
eBook - PDF- Kostas Kampourakis(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
Another important idea in that book by Morgan and his colleagues was that genes are located sequentially on chromosomes, like beads on a string (Figure 2.4a). Figure 2.4a is indicative of how genes were conceived as discrete parts of chromosomes. Morgan and his collaborators had realized that several genes were not inherited independently; in contrast, there was some kind of genetic linkage between them that in turn pointed to a physical linkage. In this sense, Caption for Figure 2.4 (cont.) Heredity, p. 60). (b) How crossing over of homologous chromosomes occurs during meiosis. This exchange of chromosome parts creates combinations of alleles (in this case Ry and rY) that did not exist in the parents. THE ORIGIN AND EVOLUTION OF THE GENE CONCEPT 43 genes could be conceived as beads on the same string. This conceptualization was essential for the techniques used by Morgan and his colleagues for mapping genes, and for the process of crossing over depicted in Figure 2.4a. Crossing over is the phenomenon of exchange of chromosome parts between two homologous chromosomes during meiosis (Figure 2.4b), which results in new combinations of genes in offspring that did not exist in their parents. The first genetic map – that is, the first map showing the linear arrangement of genes on chromosomes – had been published in 1913 by Alfred Sturtevant, a student of Morgan. In that paper, Sturtevant also set out the logic for genetic mapping. The number of crossovers per 100 cases was used as an index of the distance between any two genes (still described as factors in that paper). If one could thus determine the distances between genes A and B and between genes B and C, one would also be able to predict the distance between genes A and C. Therefore, the relative positions of genes could be empirically mapped on chromosomes, and this gave them a more material character than before. This understanding became possible at that time in part because of luck.
eBook - ePub- F. A. E. Crew, J. M. Dodd, Francis Knowles(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
Another American, McClung, † suggested that the characters maleness and femaleness were associated with the distribution from parent to offspring of a particular chromosome, and in 1903 W. S. Sutton, ‡ a young American postgraduate student, who later became a surgeon, gave the first satisfactory account of the exact parallelism between the transmission of Mendelian characters from generation to generation and the transmission of the chromosomes from cell-generation to cell-generation. The notion that the hereditary particles were borne by the chromosomes came to be known as the Sutton–Boveri hypothesis. It was largely because the development of cytology was actively encouraged by the geneticists of the United States in the first decade of this century that the leadership in the genetical field passed to America. FIG. 9 A. The chromosomes of the normal human male (they are already partially divided into their daughter chromosomes). B. The karyotype of the normal human male (Gk. karyon, nucleus; typos, image): a systematized array of the chromosomes of a single cell, prepared either by drawing or by photography. It is assumed that this karyotype typifies the chromosome complex of the individual as a whole and also that of the species to which the individual belongs. Suitable material, e.g. blood-film, is exposed to the action of colchicine and hypotonic citrate solution and is then fixed and stained and then squashed in order to disperse the chromosomes. The preparation is then drawn or photographed and greatly enlarged. It can then be seen that the chromosomes differ among themselves in respect of length. They are cut out of the photograph and matched in pairs according to their size. The pairs are then numbered according to their relative length, 1–22, number 1 being the largest, and 22 the smallest. The chromosomes fall into seven size groups: 1–3, 4 and 5, 6–12, 13–15, 16–18, 19 and 20, 21 and 22
eBook - PDF- Gerald Karp, Janet Iwasa, Wallace Marshall(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Each of these discoveries is discussed in the present chapter. 10.2 The Discovery of Chromosomes 435 Mendel drew the following conclusions, which are expressed in modern genetic terminology: 1. The characteristics of the plants were governed by distinct factors (or units) of inheritance, which were later termed genes. An individual plant possessed two copies of a gene that controlled the development of each trait, one derived from each parent. The two copies could be either identical to one another or nonidentical. Alternate forms of a gene are called alleles. For each of the seven traits studied, one of the two alleles was dominant over the other. When both were present together in the same plant, the existence of the recessive allele was masked by the dominant one. 2. Each reproductive cell (or gamete) produced by a plant contained only one copy of a gene for each trait. A particu- lar gamete could have either the recessive or the dominant allele for a given trait, but not both. Each plant arose by the union of a male and a female gamete. Consequently, one of the alleles that governed each trait in a plant was inherited from the female parent, and the other allele was inherited from the male parent. 3. Even though the pair of alleles that governed a trait remained together throughout the life of an individual plant, they became separated (or segregated) from one another during the formation of gametes. This finding formed the basis of Mendel’s law of segregation. 4. The segregation of the pair of alleles for one trait had no effect on the segregation of alleles for another trait. A par- ticular gamete, for example, could receive a paternal gene governing seed color and a maternal gene governing seed shape. This finding formed the basis of Mendel’s law of independent assortment. Mendel presented the results of his work to the mem- bers of the Natural History Society of Brünn; the minutes of the meeting recorded no discussion of his presentation.
eBook - PDF- Chavan, U D(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
He further suggested that the two genes are found in coupling phase or in repulsion phase, because they are present on the same chromosome (coupling) or on two different homologues chromosomes (repulsion). Such genes are then called linked genes and the phenomenon of inheritance of linked genes is called linkage by Morgan. • Chromosome Theory of Linkage : The chromosome theory of linkage of Morgan and Castle states that: (i) The genes which show linkage are situated in the same pair of chromosomes. (ii) The linked genes remain arranged in a linear fashion on the chromosome. Each linked gene has a definite and constant order in its arrangement. (iii) The distance between the linked genes determines the degree of strength of linkage. The closely located genes show strong linkage then the widely located genes which show weak linkage. (iv) The linked genes remain in their original combination during the course of inheritance. Kinds of Linkage: The phenomenon of linkage is of following two kinds: 1. Complete Linkage: Example: According to Bridge all the genes of male Drosophila remain completely linked. Further, in a mutant strain of Drosophila , the genes for bent wings (b+) and shaven bristles (svn) of the fourth chromosome exhibit complete linkage. 2. Incomplete Linkage: Example: Incomplete linkage has been observed in pea, Zea mays (maize), tomato, female ( Drosophila , Mice, poultry, and man. Here, the examples of linkage have been considered only for Drosophila and Zea mays (maize). Linkage groups All the linked genes of a chromosome form a linkage group. Because, This ebook is exclusively for this university only. Cannot be resold/distributed. all the genes of a chromosome have their identical genes (allelomorphs) on the homologous chromosome, is considered as one. The number of linkage groups of a species thus corresponds with haploid chromosome number of that species. Examples: 1. Drosophila has 4 pairs of chromosomes and 4 linkage groups.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
