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Heredity and Development PART I Some Contributions of Certain Areas of Biology to the Training of Biology Teachers Heredity and Development HERBERT PARKES RILEY Head, Departmentof Botany University of Kentucky A study of heredity and development can Since the laws of heredity have been learned contribute greatly to the training of a biology from experiments conducted on both plants teacher by making him aware of the principles and animals, training in genetics will tend to of biological inheritance, of give a teacher of biology an insight into the Downloaded from http://online.ucpress.edu/abt/article-pdf/17/1/7/14460/4438657.pdf by guest on 02 October 2021 the factors involved in de- unity of life. Not only do fundamental velopment and of the inter- principles and the physical basis of heredity relation between develop- operate in the same fashion in both Kingdoms, ment and heredity. The but also the nature of gene action is very teacher should familiarize similar in both animals and plants. Therefore, himself with the basic laws the teacher who is trained in genetics is more of Mendel, with the exten- likelv to visualize the field of biology as one sion of those laws to cover big field rather than as two largely unrelated more complex situations, disciplines, zoology and botanv. Within recent with the physical basis of years, too, studies on Neurospora, bacteria, heredity and the structure, yeast, Paramecium and other lower organisms chemical nature and behavior of the chromo- have been extensive. By showing that the somes and with the principles of variation, its same laws govern both the simple and the occurrence in nature and its measurement. more advanced forms of life, studies in hered- Other noteworthy principles and generaliza- ity well illustrate the unity of life and the tions are the theory of the gene, the nature basic similarity of all plants and animals. and importance of polygenes and the role of A study of genetics and development leads plasmagenes in heredity. Of great value in the to a better understanding of cellular organiza- training of biologists would be a description tion and the cellular basis of life. Generaliza- of some of the traits found to be inherited in tions which aid in an understanding of these human beings and some information about the principles are the elaborate mechanism of methods which have been used to determine mitosis which ensures that the daughter cells their basis. hereditary Generalizations and receive the same number of chromosomes as theories important to a knowledge of develop- one another and as the cell which divides to ment are: the of tissues and folding the migra- produce them, the self-duplication of proteins, tion of cells during the of the embryology the reproductive capacity of cell constituents animal; the differentiation of germ layers in such as chromosomes, genes and mitochondria, animals and the differentiation of plant cells and the constancy of the chromosomes from from meristematic tissues; the importance of one cell generation to another. hormones and of other biochemical substances produced during development as understood In recent years, experiments on Drosophila from the transplantation of eye primordia in transplants and on Neurospora and other considerable infor- Drosophlia; the nature of genetic blocks in lower plants have yielded mation as to the inheritance of fundamental chains of chemical reactions during the de- biochemical processes. These studies have also velopment of and plants animals; organizers led to a better understanding of biochemistry and axial gradients; heterogonic growth; the in general and could well contribute to the germ layers and the development of the leaf training of a biology teacher. A discussion of and flower as demonstrated by induced biochemical processes shows that they are chromosomal periclinal chimeras. under the control of genes and that many of 7 8 THE AMERICAN BIOLOGY TEACHER January 1955 these processes are absolutely essential to life; types of chromosome aberrations, the haz- that genetic blocks can arise by mutation ards of overdoses of radiation and the use of which interrupt the chain of chemical reac- radiation in the treatment of cancer. tions; and that some fundamental biochemical Finally, genetics courses help to dispel some reactions in humans are under genetic control of the old notions which have no scientific and certain people who have mutant genes are basis. These "old wives' tales" die hard. Under unable to carry out certain important chemical this point might well be discussed the in- syntheses. heritance of acquired characters, biogenesis, Although the earlier work in genetics dealt telegony, and maternal impressions, including with higher plants and animals almost exclu- the difference between maternal impressions sively, numerous studies on lower organisms in the old sense and the effect of the placental have been carried out during the last fifteen environment of the child. years. Coupled with important cytological Downloaded from http://online.ucpress.edu/abt/article-pdf/17/1/7/14460/4438657.pdf by guest on 02 October 2021 observations, they have increased greatly our knowledge of reproduction, life cycles, and Recorder's Report of Discussion on cellular structures in these lower forms. Items of general interest to the biology teacher HEREDITYAND DEVELOPMENT would be sexual reproduction in bacteria and There is a body of subject matter called yeast, the bacterial nucleus, the nucleus and biology. It is neither botany nor zoology. cellular structure of yeast, and mitosis in lower Genetics is a biological subject. Training in organisms. genetics can therefore be of great value to a While problems of speciation and hybridiza- biology teacher. It can help to give a teacher tion may be discussed in the section on Evolu- a perspective of biology as a unified whole. tion and Paleontology, they involve the An understanding of mitosis and meiosis is hereditary mechanism and can appropriately fundamental to an understanding of genetics. be taken up here, also. They involve such The chromosomes and their mitotic activity topics as gene mutation, polyploidy and other should be studied rather carefully. Meiosis is chromosomal aberrations, hybridization be- a much more complex process than mitosis, tween species, and the importance of allo- and though certain aspects such as reduction polyploidy in rendering hybrids fertile. Iso- and crossing over need to be known thor- lating mechanisms and the appearance of oughly, care should be exercised in the selec- hybrid swarms can be studied in this group as tion of the remaining material which is pre- well as in the group on evolution. sented. Life cycles are important and need to A biology teacher should be prepared to be stressed. Internal and external environments discuss the age-old problem of heredity and should be recognized and carefully considered environment. It should be pointed out that when studying the characteristics of organ- this problem is no longer pertinent and that isms. it is replaced today by a study of the action After the study of the cell and its activities, and effects of different genes acting in differ- certain other areas of genetics seem to repre- ent environments, for the developed character sent a minimum of recommended knowledge: is the result of the cooperation of the geno- 1. lendel's basic laws (monohybrid, di- type, the cytoplasm and the environment all hybrid ratios). operating together during the development 2. Polyhybrids-trihybrids, etc. gives the of the individual. Phenocopies could be in- student some conception of the mathe- troduced in this discussion. matics on which genetics is based. Since the explosion of the first atomic 3. Sex inheritance and sex linkage-mostly bomb, great interest has centered around the an animal approach. effects of radiation on living organisms. 4. Linkage and crossing over: genes on Courses in genetics should be helpful as they chromosomes; linear order; an appreci- frequently discuss the effects of radiation on ation of linkage. the hereditary mechanism and include topics 5. Mlutations and the mutation process. The such as the induction of gene mutations, both action of genes. Genes are not entirely lethal and visible, the production of various stable. Volume 17, No. 1 HEREDITY AND DEVELOPMENT 9 6. Biochemical genetics. Shows the mutual plex areas as human genetics.2 "The easiest relationshipsbetween chemistryand gene- way to confuse a student is by lack of in- tics. formation." 7. Polygenes-quantitative characters;inter- 2. Laboratory is helpful in the study of action of genes. genetics, but not an absolute essential. It is 8. Radiationeffect on hereditarymechanism helpful and probably essential that teachers -speeds up process; not new, repetition and studentssee chromosomes,and demonstra- of same things already discovered in tions of fruit flies, biochemical inheritance (Neurospora), P. T. C. taster leaflets,etc. nature. 9. Populationgenetics-not very deeply, be- Analysis of human family histories, and cause of mathematicalrequirement. study of newspaperclippings concerned with genetics are worthwhile activities, as is the 10. Human genetics and eugenics. field trip to a greenhouse,museum, or places Downloaded from http://online.ucpress.edu/abt/article-pdf/17/1/7/14460/4438657.pdf by guest on 02 October 2021 Genetics for high school teachers can be outside the school building where variation descriptive as opposed to mathematicaland genetic and environmental) can be seen in quantitative.'This does not mean that teachers many plants and animals. should not be given some of the statistical 3. Genetics can explain and remove many treatment so important to the field, but that false ideas. Mlisconceptionand prejudiceoften the amount and kind of mathematicsshould go hand in hand. be tempered with the needs and abilities of 4. The history of genetics can be effectively the students kept in mind. A minimum is integratedinto the total genetics course. represented by insisting that teachers have 5. A basis can be provided to understand the opportunity to see examplesof the statis- practicalplant and animalbreeding.
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