Law of Independent Assortment

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  Social Mendelism

  Genetics and the Politics of Race in Germany, 1900–1948

  • Amir Teicher(Author)
  • 2020(Publication Date)
  • Cambridge University Press

    (Publisher)

  In one of them, there are only two Mendel- ian laws. The first law is the Law of Segregation, which states that in sexually reproducing organisms, the hereditary factors received from both parents for any given trait do not blend into each other but remain separate. When the organism reproduces, it passes on to each of its descendants, with equal probability, either the factor it received from its father or the one from its mother. As a result, when conducting controlled hybridization experiments, it is possible (in principle) to com- pute the chances that a certain trait will appear among the progeny. The second law, the Law of Independent Assortment, states that factors for different traits are inherited independently of each other. For example, the color of the pea and its height are different traits; therefore, their respective hereditary factors are mutually independent. 22 In the alternative version, there exist three Mendelian laws. The first is the Law of Uniformity (Uniformitätsregel), which states that all the 21 This has allowed for considerable scope of interpretation regarding Mendel’s real objectives in constructing his experiments as well as in compiling his paper, and consequently also regarding the essence of Mendel’s work in Mendel’s own eyes. The scholarly debate on these matters has yielded a range of thought-provoking studies and unorthodox historical interpretations. For example, see Robert Olby, “Mendel no Mendelian?” History of Science 17 (1979): 53–72; Alain F. Corcos and Floyd V. Monaghan, “The Real Objective of Mendel’s Paper,” Biology and Philosophy 5 (1990): 267–292; Raphael Falk and Sahotra Sarkar, “The Real Objective of Mendel’s Paper: A Response to Monaghan and Corcos,” Biology and Philosophy 6 (1991): 447–451; Floyd V.

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  Biology for AP® Courses

  • Julianne Zedalis, John Eggebrecht(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  The role of the meiotic segregation of chromosomes in sexual reproduction was not understood by the scientific community during Mendel’s lifetime. Independent Assortment Mendel’s Law of Independent Assortment states that genes do not influence each other with regard to the sorting of alleles into gametes, and every possible combination of alleles for every gene is equally likely to occur. The independent assortment of genes can be illustrated by the dihybrid cross, a cross between two true-breeding parents that express different traits for two characteristics. Consider the characteristics of seed color and seed texture for two pea plants, one that has green, wrinkled seeds (yyrr) and another that has yellow, round seeds (YYRR). Because each parent is homozygous, the law of segregation indicates that the gametes for the green/wrinkled plant all are yr, and the gametes for the yellow/round plant are all YR. Therefore, the F 1 generation of offspring all are YyRr (Figure 12.16). 496 Chapter 12 | Mendel's Experiments and Heredity This OpenStax book is available for free at http://cnx.org/content/col12078/1.6 Figure 12.16 This dihybrid cross of pea plants involves the genes for seed color and texture. In pea plants, purple flowers (P) are dominant to white flowers (p) and yellow peas (Y) are dominant to green peas (y). What are the possible genotypes and phenotypes for a cross between PpYY and ppYy pea plants? What is the minimum number of squares that you need to do a Punnett square analysis of this cross? a. ppYY, Ppyy, ppYY, ppyy yielding white flowers with yellow peas, purple flowers with yellow peas, and white flowers with green peas. You can find this with a 3×3 Punnett square. b. PPYY, PpYy, ppYY, ppyy yielding purple flowers with yellow peas, white flowers with yellow peas, and white flowers with green peas.

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  Discoveries In Plant Biology (Volume I)

  (Volume I)

  • Shang-fa Yang, Shain-dow Kung(Authors)
  • 1998(Publication Date)
  • World Scientific

    (Publisher)

  If any other gene pair behaves independently the same way, then independent assortment occurs. However, the actual mechanism was unknown until chromosomes were discovered and the Chromosome Theory of Heredity was published by Walter Sutton (1903). Boveri's (1904) work established a crucial connection between cytology and Mendel's laws and furnished a rigorous proof that the chromosome location of genes is responsible for equal segregation and independent assortment. Mendel further correctly deduced that if n represents the number of the differentiating characters in the two original parents, 3 n gives the number of combination series, 4 n the number of individuals that belong to the series, and T the number of unions that remain constant (homozygous). For example, when n=2, like round vs wrinkled and 154 George H. Liang, D. Z. Skinner, Yi Sun, E. L. Sorenson and J. H. Guo yellow vs green, in F 2 there will be 3 2 = 9 combinations (RR YY, Rr YY, ... rryy); 4 2 = 16 individuals in the series (9 + 3 + 3 + 1); 2 2 = 4 homozygous zygotes (RR YY, RR yy, rr YY, and rr yy). Nearly four decades after Mendel's work, the definitive confirmation and clarification of the law governing the inheritance of individual traits finally came, thanks to the independent work of three scientists; Hugo de Vries, a Dutchman; Carl Correns, a German; and Erich Tschermak, an Austrian. None of them probably had heard of Mendel when they began their experiments. In 1900, de Vries published Concerning the Law of Segregation of Hybrids and The Law of Segregation of Hybrids (Sturtevant, 1965), Correns submitted his paper, G. Mendel's Law Concerning the Behavior of the Progeny of Racial Hybrids (Sturtevant, 1965) (he was acquainted with Mendel's work after he had terminated his own experiment), and Tschermak published his study entitled, Concerning Artificial Crossing in Pisum sativum (Sturtevant, 1965).

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  Genetics For Dummies

  • Rene Fester Kratz, Lisa Spock(Authors)
  • 2023(Publication Date)
  • For Dummies

    (Publisher)

  Sin- gle pairs of genes (that is, one locus) control each trait. That means that plant height is at one locus (controlled by one gene), seed color at a different locus, seed shape at a third locus, and so on. FIGURE 3-4: The principles of segregation and dominance as illustrated by three generations of pea plants with green and yellow seeds. CHAPTER 3 Visualize Peas: Discovering the Laws of Inheritance 45 Declaring independence As Mendel learned more about how traits were passed from one generation to the next, he carried out experiments with plants that differed in two or more traits. He discovered that the traits behaved independently — that is, that the inheritance of plant height had no effect on the inheritance of seed color, for example. The independent inheritance of traits is called the Law of Independent Assortment and is a consequence of meiosis. When homologous pairs of chromosomes sepa- rate, they do so randomly with respect to each other. The movement of each indi- vidual chromosome is independent with respect to every other chromosome. It’s just like flipping a coin: As long as the coin isn’t rigged, one coin flip has no effect on another — each flip is an independent event. Genetically, what this random separation amounts to is that alleles on different chromosomes are inherited independently. Segregation and independent assortment are closely related principles. Segregation tells you that alleles at the same locus on pairs of chromosomes separate and that each offspring has the same chance of inheriting a particular allele from a parent. Independent assortment means that every offspring also has the same opportunity to inherit any allele at any other locus (although this rule does have some excep- tions, which are described in Chapter 4). Predicting with Punnetts Mendel’s discoveries opened the door to the science of genetics. One British geneticist who continued Mendel’s studies was Reginald C.

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  Primer of Genetic Analysis

  A Problems Approach

  • James N. Thompson, Jr, Jenna J. Hellack, Gerald Braver, David S. Durica(Authors)
  • 2007(Publication Date)
  • Cambridge University Press

    (Publisher)

  CHAPTER FOUR Basic Mendelian Genetics STUDY HINTS Although Mendel did not know about the events that occur in a dividing cell, his laws of segregation and independent assortment are really descriptions of chromosome behavior during meiosis. Segregation simply refers to the fact that the two homol- ogous chromosomes separate to opposite sides of the cell (that is, they segregate) after synapsis in the first meiotic division. Independent assortment reflects the fact that the orientation of one pair of homologous chromosomes at the equatorial plate in cell division is independent of the orientation of other pairs; that is, alignment of chromosomes occurs randomly relative to one another. The secret to solving Mendelian genetics questions is to recognize that there is a pattern hidden within the superficial confusion of facts with which you are presented. The first important step is to have a clear understanding of mitosis and meiosis. Then you must have a thorough working knowledge of the terminology. Beginning students commonly confuse phenotype and genotype, or gene and allele. Genotype is the genetic makeup (such as Aa), whereas phenotype is the expression of the genotype interacting with its environment (such as brown versus black fur). Different genes code for totally different protein products (such as a pigment enzyme versus blood membrane protein), whereas alleles are the different forms that a specific gene can have (such as normal enzyme A versus the lower-activity form of the same enzyme a). A list of Important Terms is given at the end of this section, and definitions can be found in the Glossary. We recommend that you use this list of terms as a study aid to test your own ability to define terms. Set up flash cards for difficult terms. Remember that beginning to study a new science is not very different from beginning to learn a foreign language.

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  Key Notes on Agriculture Botany

  • Chavan, U D(Authors)
  • 2021(Publication Date)
  • Daya Publishing House

    (Publisher)

  This ebook is exclusively for this university only. Cannot be resold/distributed. For example, the F 1 hybrids (Tt) of a monohybrid cross between tall (TT) and dwarf (tt) pea plant has one dominate allele (T) for tallness and one recessive allele (t) for dwarfness. This genotype of F 1 hybrids remains the same from the unicellular zygote stage to the gametogenesis stage of multicellular adult plant. These F 1 hybrids by selffertilization produce tall and dwarf plants in the ratio of 3 : 1. It means that tall and dwarf alleles though, remain together for long time but does not contaminate or mix with any one and both alleles segregate to produce gametes which either having dominant allele T or recessive allele t. These gametes unite to produce the 3 : 1 phenotypic ratio in F 2 . This ebook is exclusively for this university only. Cannot be resold/distributed. Mendel’s Law of Independent Assortment Mendel’s Law of Independent Assortment or recombination off genes states that when the gametes are formed the members of the different pairs of factors (genes) segregate quite independently of each other and that all possible combinations of the factors (genes) concerned will be found among the progeny. (figure on next page). Vapour and Fluid Theory Early Greek philosophe rs speculated that the hereditary informations of parents existed in the form of vapours of fluids. Pythagoras (500 B.C.) speculated that a moist “vapour” descended from the brain, nerves and other body organs of the male during the coitus and from these vapours an embryo was formed in the uterus of the female. According to him, the male transmitted all the characters of the embryo and the female does not. However, another Greek philosopher of the same age, Empedocles thought that both parents contributed equally to the embryo and each parent produces “semen” which arises directly from various body parts.

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  Philosophy of Biology

  A Contemporary Introduction

  • Alex Rosenberg, Daniel W. McShea(Authors)
  • 2007(Publication Date)
  • Routledge

    (Publisher)

  It does not take much more examination than that to conclude that Mendel’s laws are not, after all, really laws at all. Mendel did his famous experiments on pea plants in the mid-nineteenth century. His published results went unnoticed until rediscovered in the early twentieth century and, since then, a major theme of the history of genetics has been the discovery of more and more exceptions to his laws. Luckily for Mendel and for genetics, the traits he first studied did not happen to involve genes located close together on the same chromosomes. Had they been so “linked,” that is lying close together on the same chromosome, they would not have assorted independently. Once linkage was detected, it became clear that the second law is a rough and ready generalization with enormous numbers of exceptions, such as those arising from linkage. As for the law of segregation, geneticists now know cases in which segregation is unequal, in which one of the two alleles is preferentially transmitted to the next generation, the so-called segregation distorter alleles.

  Of course, just because Mendel’s principles are not laws does not mean that they are not important in biology. What it does mean is that when they are successfully applied in prediction, and when they are not, is a matter to be explained by appeal to other more fundamental regularities. In the case of Mendel’s laws, these will be regularities about meiosis and other details of cell physiology. Is that where the laws are? Somewhere in these lower level processes, is that where we will find the fundamental causal laws of biology that explain Mendelian generalizations and their exceptions?

  The answer is almost certainly not. Again, the reason goes back to Darwinian theory. For the theory tells us that meiosis, segregation, and assortment are—like other features of organisms such as genes, chromosomes, and sexual reproduction—the result of a long evolutionary history. In the course of that history, natural selection produced adaptation, including both the Mendelian processes themselves—such as meiosis that produces segregation—and other non-Mendelian processes, some of which—such as segregation distorters—take advantage of Mendelian processes. Future environmental changes could modify meiosis further, or even do away with it altogether. Similarly, if natural selection is operating on other worlds circling other suns, we have some reason to suppose that there will be replicators and perhaps also interactors on these worlds but little reason to suppose that they will reproduce by meiosis, or that anything like Earthly sexual physiology will have emerged. The domain of any laws that we discover about sexual processes, or about anything else in biology, could well be quite limited, that is to say limited to a single instance of biology here on Earth and further limited to a particular time range in Earthly evolutionary history.

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  The Selected Works of C. H. Waddington (7 vols)

  • C. H. Waddington(Author)
  • 2021(Publication Date)
  • Routledge

    (Publisher)

  The mutant allelomorphs of the locus are written with small letters unless they are dominant over the wild (e.g. vv« eosin, w«> coral are allelomorphs of white, Bd beaded is dominant over the wild allelomorph). The cross of the wild type gene is now often written as an exponent, e.g. w+. Complex heterozygotes may be written AoBBCc, or the genes in one chromo some may be separated from those in the homologue by a dot (e.g. ABC.aBc) or a line (e.g. - f + +/we + f, where the two recessives we and f occur in the same chromosome). 3. Mendel's Second Law: Independent Assortment Mendel’s original experiments dealt with the inheritance of several characters simultaneously: tall or short plants, round or wrinkled seeds, etc. Each pair of allelomorphs was found to behave quite independently of every other pair. In a double heterozygote AaBb half the germ cells will of course contain A 9 and of these, it was pure chance which con tained B and which byso that the combinations A B and Ab were found in equal numbers. P1 . Round Yellow RR YY X Wrinkled Green rr yy (germ cells RY) | (germ cells ry) F1 Round Yellow RY ry (germ cells 1RY: 1Ry : 1rY : 1ry) V/ 4 1 RY 1 Ry 1 rY 1 ry FI. 1 V \Y RRYY RRYy RrYY RrYy 1 Ry RRYy RRyy RrYy Rryy 1 rY RrYY RrYy rrYY rrYy 1 ry RrYy Rryy rrYy rryy Total of the F2. 9 with R and Y, showing Round Yellow. 3 with R and y, showing Round Green. 3 with r and Y, showing Wrinkled Yellow. 1 with r and y, showing Wrinkled Green. This is known as the “ chequerboard” method of finding the progeny of a cross. An alternative is to multiply the two series of gametes together algebraically, e.g. to get the F2 above we have (RY + Ry rY + ry) (RY 4- Ry + rY -f ry) —RRYY + 2RRYy + 2RrYY + URrYy + RRyy + IRryy + rrYY + 2rrYy + rryy. Fig. 2. IndepenJent Assortm ent of Factors in a cross between round yellow and green wrinkled peas (Mendel).

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  Introduction to Genetics

  11th Hour

  • Sandra Pennington(Author)
  • 2009(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  These progeny are unlike any plants seen before in this experiment in that color and shape are combined dirrercmly in the F\! generation than they were in the P generation. A less obvious aspect is that the frequency at which these exceptionaJ progeny appear is consistent with random reassortmem of the characters or genes. If the gametes that form these progeny (gill and Gw) did not occur at the same frequency as the other two gametes (i.e., the "paremal" gamt"tt"s, Gill and gw), a ratio other than 9: 3: 3: 1 would have occurred. (In Chapter 4, we will examine the situation where reassorunem is not random. Suffice it to say now that we can recognize non- random assortment of genes by an aJtered 9: 3: 3: I dihybrid ratio.) recognized the randomness that is needed to create this distinctive ratio and correcLly inferred from it the phenomenon that would be described by his principle of independent assortment. This principle states that the fate of one character (seed color) is independent of the other character (seed shape). In modern terms, we say that the segregation of alleles of one gene is independent of that of alleles of a second gene. The proof of this statement is the appearance of non- parental combinations or phenotypes in the proportions 3/16 green round seeds and 3/16 yellow wrinkled seeds in the generation. Topic Test 5: Independent Assortment True/False I. The green round progeny in the cross discussed in this topic art: dearly produced by independent assortment of genes. 2. The principle of indcpcndenl a.ssurtment means that green and yellow will sometimes appear in the same seed. Multiple Choice 3. The dihybrid ratio 9: 3: 3: I refers to a. genotypes. b. phenotypes. 12 Chapter 1 Mendelian Inheritance c. gametes produced by the dihybrid. d. the number of generations needed to get a heterozygote. 4. The cross (by genotype) that produces progeny in the ratio 9:3:3: I can be generalized: a. AaBb X AaBb h. AAbb X •• /111 c. AaBb X aabb d. AAbb X AaBb e.

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  Introduction to Molecular Biology, Genomics and Proteomics for Biomedical Engineers

  • Robert B. Northrop, Anne N. Connor(Authors)
  • 2008(Publication Date)
  • CRC Press

    (Publisher)

  genetics. .Mendel.used.pea.plants.as.his.model,.cultivating.and.testing.some.28,000.plants.[Field. Museum.2007] . .He.discovered.that.dominant.and.recessive.genes.combine.in.specific,.predictable. ratios.in.each.generation . .Mendelian.inheritance.can.be.summarized.in.generalizations.known.as. Mendel’s Laws of Heredity: Mendel’s First Law: The Law of Segregation . .During.gamete.formation,.each.member.of.the. allelic.pair.(of.genes).separates.from.the.other.member,.ensuring.variation . .In.other.words,. the.expression.of.the.dominant.allele.does.not.eliminate.the.recessive.allele.in.the.pair.but. merely.suppresses.it . .Thus,.a.recessive.gene.can.be.passed.on.through.the.generations,.even. when.the.phenotype.is.not.expressed . Mendel’s Second Law: The Law of Independent Assortment . .During.gamete.formation,.each. allelic.pair.separates.independently.of.all.other.allelic.pairs . .This.is.the.essence.of.Men-del’s.conceptual.breakthrough—genetic.inheritance.happens.in.discrete.units . Linked Genes: .During.his.experiments,.Mendel.encountered.an.exception.to.the.second.law . .Some. traits.did.not.appear.independently.but.always.appeared.together.with.at.least.one.other.trait.(e .g., . red.hair.and.a.pale.complexion.are.often.linked).[Hunter.&.Mitchell.1997] . .Today,.we.know.that. some.genetic.traits.are.located.close.to.one.other.on.a.chromosome.and.tend.to.be.linked,.or.inher-ited.together . .Therefore,.Mendel’s.Law.of.Independent.Assortment.only.applies.to.genes.on.differ-ent.chromosomes . Mendelian F2 Ratios: .Mendel.found.that.mixing.parents.with.different.forms.of.the.same.trait. yields.a.3:1.ratio.between.dominant.and.recessive.phenotypes.in.the.offspring.(see.Table.5 .1). Example :.Red.versus.white.flowers.in.pea.plants . .Recessive.alleles.are.indicated.with.lowercase. letters. Exceptions to the F2 rule: .Despite.his.large.sample.sizes,.Mendel.did.not.find.perfect.3:1.ratios.

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