DOCSLIB.ORG

Mendel, Human Genetics, & the Gene Idea

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mendel, Human Genetics, & the Gene Idea Genetics Mendel, Human Genetics, & The Gene Idea Genetics . Genetics -the study of inheritance. -how traits (characteristics) are passed down from parent to offspring. Gregor Mendel- mid 1800’s-Austrian monk -founded modern genetics with data gathered from growing peas. Peas -easy to grow and had many traits. Self-pollinate and cross-pollinate* Flower Anatomy Pollen is here Eggs are here Pollen grains and eggs Pollen is flower sperm Ovules are eggs at the flower base Mendel’s Terms Trait (variant for a character, i.e., brown) True-breeding (all offspring of same variety) -Pure-Breed Hybrid (offspring of 2 different true-breeds) Alleles- different forms of gene P generation (parents) F1 generation (first generation) F2 generation (second generation) Mendel’s Experiments: Self and Cross Pollinated 1. Focused on -garden pea traits by crossing different traits one at a time: Flower/seed coat color: gray vs white Seed color: yellow vs. green Seed shape: smooth vs. wrinkled Pod color: green vs. yellow Pod shape: inflated vs. pinched Stem height: tall vs. short Flower position: axial vs. terminal 2. Counted offspring of each trait form and analyzed the results using math. Vocabulary . Alleles –forms of a gene. Homozygous: pair of identical alleles for a trait . (pure/true-bred) . Heterozygous: two different alleles for a trait . (Hybrid) . Phenotype: an organism’s observed trait . Genotype: an organism’s genetic makeup Law of Segregation . Different alleles account for variations in inherited characteristics . For a trait-an organism inherits 2 alleles, one from each parent . Alleles - segregate (separate) during gamete production (meiosis). Probability and Punnett squares Punnett square- a tool to calculate expected genotypes of offspring of a cross. Principle of Dominance Heterozygous offspring, (Aa) . Dominant allele- fully expressed in the organism’s phenotype . Recessive allele, has no effect on the organism’s phenotype . (* 1 pattern of inheritance) Law of Independent Assortment . Alleles on different chromosomes, segregate independently of each other= . Mendel’s Law of Independent Assortment Dihybrid F1 generation Two traits- Two different chromosomes 2 homozygous Parents with different traits produce Dihybrid offspring Dihybrid cross: F2 generation Phenotype Ratio: 9:3:3:1 Additional Genetic Patterns Mendel’s peas Other Patterns Complete Incomplete Dominance Dominance Codominance Lethal Alleles Two alleles /gene Multiple Alleles One gene affects …Many characteristics one trait (Pleiotropy) Two (or more) genes affect one trait (Polygenic Traits) One gene masking another(Epistasis) Other Inheritance Patterns . Incomplete dominance - appearance between the phenotypes of the 2 parents. Ex: snapdragons CR=red CW=white Pink- heterozygous CRCW Recognize- Different allele representation Incomplete Dominance Problem Snapdragon problem: Use the allele representation C R = Red, C W = white The outcome of a cross between a red- flowered plant and a pink-flowered plant? P = C R C R x C R C W 50% red, C R C R 50% pink, C R C W Sometimes Genotype Written: RR, RW Incomplete Dominance Incomplete dominance: neither allele masks the other and both are observed as a blending in the heterozygote RR x R’R’ Four o’clock flowers Red White R = red, R’ = white RR’ pink Incomplete Dominance RR’ x RR’ Pink x Pink Genotypic Ratio: Phenotypic Ratio: Codominance . Codominance: two alleles equally expressed, but not blended, like incomplete dominance . Ex: Roan coat- cows- both red and white hairs Cross a red cow with a white bull. What is the expected genotype and phenotypes of the offspring? P = RR x WW RW, roan Multiple Alleles -Having more than 2 alleles for a trait. Human Blood alleles- IA ,IB, i codominance & multiple IA = IB > i IA and IB are codominant. IA and IB are completely dominant over i. Antigens on Red Blood Cells IAi IBi IAIB Lethal Alleles Gene capable of causing death- usually in embryo. Example: Manx cat ML = tailless, lethal in homozygote m = tail Tailless male x Tailless female Polygenic Traits . Most of your traits are controlled by the interaction of many genes. Multiple genes working together produce a continuous distribution in a “Bell Shape” curve of degrees. Examples of Polygenic Traits Individual genes of a . Body Type polygenic trait follow . Height Mendel's laws but . Skin Color together do not . Hair color produce Mendelian . Eye color ratios. Intelligence . We often see the famous “Bell Curve” Example of Polygenic Inheritance Two genes affecting skin coloration Number of Skin Color* Genotypes % Pigmentation Dominant (Phenotype) Alleles 0 White aabb 0-11% 1 Light Black Aabb or aaBb 12-25% 2 Medium Black AAbb or AaBb or 26-40% aaBB 3 Dark Black AABb or AaBB 41-55% 4 Darkest Black AABB 56-78% *Based on a study conducted in Jamaica. Polygenic Inheritance Medium Black Woman X Darkest Black Man (mother is white) Pleiotropic Effects One gene affects many phenotypic characteristics Allele S S’ Gene Product Hemoglobin A Hemoglobin S Cell Shape Round Sickled under low O2 tension Response to Susceptible Resistant in SS’ Malaria genotype Pleiotropy Pleiotropy refers to an allele which has more than one effect on the phenotype. This can be seen in human diseases such as cystic fibrosis or sickle cell anemia. In these diseases, multiple symptoms can be traced back to one defective allele. Recent studies show … . Hypertension . Diabetes . Cancers . Allergies . Cardiovascular diseases . Behavioral traits (alcoholism and phobias) …..have some genetic link but also environmental explanation. Environmental Effects Expression of some genes may be impacted by environment Gene for pigment production expressed in cooler regions of body Another example of environmental influence: . Hydrangeas – same genotype, different environments different color flowers Acid pH Alkaline pH Epistasis . An allele of one gene masks the expression of alleles of another gene and expresses its own phenotype instead. Gene that masks = epistatic gene . Gene that is masked = hypostatic gene Epistasis . Action of genes at one location modify expression genes at another location .Effects often complex . Examples . Coat color in Labrador dogs . Snake coloration Epistasis in Labrador Dogs . Bb or BB dark (black) pigment produced . bb light (brown) pigment produced . Ee or EE deposition of melanin . ee deposition of pigment blocked Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ee E_ No dark pigment in fur Dark pigment in fur Yellow Lab E_bb E_B_ eebb eeB_ Chocolate Lab Black Lab Yellow fur; Yellow fur; Brown fur, Black fur, brown nose, black nose, nose, lips, nose, lips, lips, eye rims lips, eye rims eye rims eye rims Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes One gene O = orange pigment o = no orange pigment Second gene B = black pigment b = no black pigment Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes Oo Bb x Oo Bb OB Ob o B o b OB OO BB OOBb Oo BB Oo Bb Ob OO Bb OO bb Oo Bb Oo bb o B Oo BB Oo Bb o o BB o o Bb o b Oo Bb Oo b b o o Bb o o b b Interacting Genes Affecting a Single Characteristic eg. Skin coloration in snakes OoBb x OoBb 9/16 O_B_ 3/16 O_bb 3/16 ooB_ 1/16 oobb Ch 14 Gene Disorders – Gene Mutations . Gene disorder -the harmful effect a mutated allele produces when it occurs with significant frequency in a population. Can be inherited in several ways Dominant/ recessive Codominance Recessive Disorders Ex PKU - phenylketonuria CF -Cystic fibrosis Tay-Sachs Albinism Prader-Willi Gene Disorders Phenylketonuria (PKU) A recessive disorder that occurs in 1 of 10,000 people. A defective gene on chromosome 12 is responsible. Cannot break down -Amino acid phenylalanine. Recessive Disorders Cystic Fibrosis A recessive disorder - mutated gene on chromosome 17. Excessive secretion of the mucus in the body. Tay-sachs Disease A recessive disorder that occurs in 1 of 5,000 people - European Ashkenazi Jews Defective gene on chromosome 15. Excess lipids in brain Prader Willi Syndrome A recessive disorder that occurs in 1 of 15,000 people. Determined by a set of Mutated genes on chromosome 15. Dominant Disorders Marfan’s Syndrome Huntington’s disease Osteogenesis imperfecta Neurofibromatosis (NF) Huntington Disease A dominant disorder that occurs in about 1 of 10,000 people. A dominant gene on chromosome 4 is responsible. It causes degeneration of neurons producing dementia, and random jerking movements. Other Patterns of Inheritance Multiple Alleles: ABO Blood Group . Codominance - No single allele is dominant, and each allele has its own effect. Blood alleles A and B Recessive . Blood O allele Human Blood Types Phenotype Genotype O i recessive A IA IA or IAi B IB IB or IB i AB IAIB Inherited traits and disorders can be… . Autosomal – non-sex chromosomes(1-22) ex sickle cell, CF, PKU . Sex-Linked – sex chromosomes (23rd) . A sex-linked trait is expressed by a gene on the sex chromosomes . We study traits on the X chromosome. Human Chromosomes . 22 of the pairs are called autosomes and are numbered from largest to smallest. The 23rd pair are the sex chromosomes: . XX females . XY males Chromosomes Sex-Linked Gene Disorders 1- Color Blindness Recessive disorder. Occurs in 1 of 10 males, green –red most frequent 2- Hemophilia A and B Recessive disorders that affect 1 of 5,000 males. Interferes with normal blood clotting and occur at positions on a chromosome on the X chromosome. Sex Linked Genetics problems -must include the chromosomes when doing problems. X Y The allele is superscripted on X H h X Y or X Y H=normal h=hemo Pedigrees Pedigrees - used to study inheritance of trait over generations Ex. hemophilia - inherited condition where blood is slow to clot or does not clot at all . Royal hemophilia - sex-linked You must learn how to analyze a pedigree! Make sure you understand the symbols and shading as we study the pedigrees on your problem sheet.
Load more

Recommended publications
  • Biology Incomplete Dominance 5E Model Lesson
    BIOLOGY INCOMPLETE DOMINANCE 5E MODEL LESSON Teacher: Expected Length of Lesson Topic: Unit: Heather Lesson: Incomplete Genetics Yarbrough 1 - 90 minute class Dominance SB3. Obtain, evaluate, and communicate information to analyze how biological traits are passed on to successive generations. Targeted Content Standards/ b. Use mathematical models to predict and explain patterns of inheritance. Element: (Clarification statement: Students should be able to use Punnett squares (Include the entire standard) (monohybrid and dihybrid crosses) and/or rules of probability, to analyze the following inheritance patterns: dominance, codominance, incomplete dominance.) L9-10RST2: Determine the central ideas or conclusions of a text; trace ​ the text’s explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text. L9-10RST7: Translate quantitative or technical information expressed in ​ words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words. L9-10RST9: Compare and contrast findings presented in a text to those Targeted Literacy Skills or ​ Standards: (include as many as your from other sources (including their own experiments), noting when the ​ lesson incorporates) findings support or contradict previous explanations or accounts. L9-10WHST2: Write informative/explanatory texts, including the ​ narration of historical events, scientific procedures/ experiments, or technical processes. d. Use precise language and domain-specific vocabulary to manage the complexity of the topic and convey a style appropriate to the discipline and context as well as to the expertise of likely readers. L9-10WHST4: Produce clear and coherent writing in which the ​ development, organization, and style are appropriate to task, purpose, and audience.
    [Show full text]
  • Genetics in Harry Potter's World: Lesson 2
    Genetics in Harry Potter’s World Lesson 2 • Beyond Mendelian Inheritance • Genetics of Magical Ability 1 Rules of Inheritance • Some traits follow the simple rules of Mendelian inheritance of dominant and recessive genes. • Complex traits follow different patterns of inheritance that may involve multiples genes and other factors. For example, – Incomplete or blended dominance – Codominance – Multiple alleles – Regulatory genes Any guesses on what these terms may mean? 2 Incomplete Dominance • Incomplete dominance results in a phenotype that is a blend of a heterozygous allele pair. Ex., Red flower + Blue flower => Purple flower • If the dragons in Harry Potter have fire-power alleles F (strong fire) and F’ (no fire) that follow incomplete dominance, what are the phenotypes for the following dragon-fire genotypes? – FF – FF’ – F’F’ 3 Incomplete Dominance • Incomplete dominance results in a phenotype that is a blend of the two traits in an allele pair. Ex., Red flower + Blue flower => Purple flower • If the Dragons in Harry Potter have fire-power alleles F (strong fire) and F’ (no fire) that follow incomplete dominance, what are the phenotypes for the following dragon-fire genotypes: Genotypes Phenotypes FF strong fire FF’ moderate fire (blended trait) F’F’ no fire 4 Codominance • Codominance results in a phenotype that shows both traits of an allele pair. Ex., Red flower + White flower => Red & White spotted flower • If merpeople have tail color alleles B (blue) and G (green) that follow the codominance inheritance rule, what are possible genotypes and phenotypes? Genotypes Phenotypes 5 Codominance • Codominance results in a phenotype that shows both traits of an allele pair.
    [Show full text]
  • Roadmap • Optimal Mutation Rate • Dominance and Its Implications
    Roadmap • Optimal mutation rate • Dominance and its implications { Why is an allele dominant or recessive? { Overdominance (heterozygote advantage) { Underdominance (heterozygote inferiority) One minute responses • Q: I don't understand degrees of freedom! (About six of these....) • Q: Show the calculation of µ and ν Degrees of freedom revisited Thanks to Patrick Runkel: http://blog.minitab.com/blog/statistics-and-quality-data-analysis/ what-are-degrees-of-freedom-in-statistics A a Total A 20 a 10 Total 15 15 One more look at degrees of freedom Fictional data for sickle-cell hemoglobin (alleles A and S) in African-American adults Normal AA 400 Carrier AS 90 Affected SS 10 • Suppose I told you: { How many people I sampled { How many of each allele I found { How many AS carriers I found • Are there any possible surprises left in the data? (AA? SS?) • This is why there is only 1 df Mu and nu • µ (mu, forward mutation rate) { mutation rate per site is observed { rate per significant site in gene is: { rate per site x number of significant sites • ν (nu, back mutation rate) { mutation rate per site is observed { need the right nucleotide (1/3 chance) { rate per site x 1/3 Is mutation good or bad? • Most mutations have no fitness effect • Of those that do, most are bad • Most organisms expend significant energy trying to avoid mutations (DNA proofreading, etc) • Are organisms trying (and failing) to reach a mutation rate of zero? • Could there be selection in favor of a non-zero rate? Transposons as mutagens • Transposons are genetic elements that
    [Show full text]
  • Dominance Hierarchy Arising from the Evolution of a Complex Small RNA Regulatory Network Eléonore Durand, Raphaël Méheust, Marion Soucaze, Pauline M
    RESEARCH ◥ between S alleles (6). Selection is expected to RESEARCH ARTICLE favor genetic elements (“dominance modifiers”), which establish dominance-recessivity interac- tion rather than codominance, because individ- PLANT GENETICS uals with a codominant genotype can produce pollen rejected by more potential mates than would occur in a dominant-recessive system (7, 8). Dominance hierarchy arising from On the basis of modeling (8), the large non- recombining region composing the S locus (9–11) is a strong candidate region for hosting such ge- the evolution of a complex small netic elements. Until recently, the dominance modifiers as- RNA regulatory network sumed in models (7, 8) remained hypothetical. A particular small RNA (sRNA) has been identified Eléonore Durand,1,2* Raphaël Méheust,1* Marion Soucaze,1 Pauline M. Goubet,1† (12) within the S locus of dominant alleles in Sophie Gallina,1 Céline Poux,1 Isabelle Fobis-Loisy,2 Eline Guillon,2 Thierry Gaude,2 Brassica (called Smi). This sRNA acts as a trans- Alexis Sarazin,3 Martin Figeac,4 Elisa Prat,5 William Marande,5 Hélène Bergès,5 modifier of the gene controlling pollen specificity Xavier Vekemans,1 Sylvain Billiard,1 Vincent Castric1‡ via de novo methylation of the promoter of re- cessive alleles, which leads to transcriptional si- The prevention of fertilization through self-pollination (or pollination by a close relative) lencing of recessive alleles by dominant alleles in the Brassicaceae plant family is determined by the genotype of the plant at the (13, 14). However, the mechanism in the more self-incompatibility locus (S locus). The many alleles at this locus exhibit a dominance complex dominance-recessivity networks in spe- Downloaded from hierarchy that determines which of the two allelic specificities of a heterozygous genotype cies that have many levels in the dominance is expressed at the phenotypic level.
    [Show full text]
  • An Introduction to Quantitative Genetics I Heather a Lawson Advanced Genetics Spring2018 Outline
    An Introduction to Quantitative Genetics I Heather A Lawson Advanced Genetics Spring2018 Outline • What is Quantitative Genetics? • Genotypic Values and Genetic Effects • Heritability • Linkage Disequilibrium and Genome-Wide Association Quantitative Genetics • The theory of the statistical relationship between genotypic variation and phenotypic variation. 1. What is the cause of phenotypic variation in natural populations? 2. What is the genetic architecture and molecular basis of phenotypic variation in natural populations? • Genotype • The genetic constitution of an organism or cell; also refers to the specific set of alleles inherited at a locus • Phenotype • Any measureable characteristic of an individual, such as height, arm length, test score, hair color, disease status, migration of proteins or DNA in a gel, etc. Nature Versus Nurture • Is a phenotype the result of genes or the environment? • False dichotomy • If NATURE: my genes made me do it! • If NURTURE: my mother made me do it! • The features of an organisms are due to an interaction of the individual’s genotype and environment Genetic Architecture: “sum” of the genetic effects upon a phenotype, including additive,dominance and parent-of-origin effects of several genes, pleiotropy and epistasis Different genetic architectures Different effects on the phenotype Types of Traits • Monogenic traits (rare) • Discrete binary characters • Modified by genetic and environmental background • Polygenic traits (common) • Discrete (e.g. bristle number on flies) or continuous (human height)
    [Show full text]
  • Lesson Plan Mendelian Inheritance
    Dolan DNA Learning Center Mendelian Inheritance __________________________________________________________________________________________ Overview • Computer with internet access This 90 minute lesson (two class periods of 45 minutes) is an introduction to Mendel’s Laws of Inheritance for students in Lesson Structure grades 5 through 8. By studying inherited traits in humans such as tasting PTC paper and inherited traits in plants such as Pre-lab (45 minutes) – Day 1 maize, we can understand how traits are passed down through Teacher Prep generations. A discussion of dominant and recessive traits in humans will encourage students to further explore their • Become familiar with Lab Center inheritance as well as their family inheritance. http://www.dnalc.org/labcenter/mendeliangenetics/m endeliangenetics_d.html Learning Outcomes • Print and copy Background Reading from the Students will be able to: Student Lab Notebook on the Lab center. • discuss the contributions of Gregor Mendel and his • Print and copy Student Pre-lab Worksheets from experiments with the garden pea. the Student Lab Notebook on the Lab center. • review the structure of DNA and chromosomes. • Cut paper strips for Sentence Strips activity. • compare a dominant trait to a recessive trait. • Make sure computers with Internet access are • compare a homozygous trait to a heterozygous trait. available. • identify traits in themselves that are either dominant or recessive. Before class • use maize as a model organism to study Mendelian Students will receive the background reading to read for inheritance. homework the night before starting lab. They will write 2 to 3 • demonstrate Mendel’s Law of Dominance and Law questions they have about the background information.
    [Show full text]
  • Incomplete Dominance, Codominance, and ABO Blood Types
    Incomplete Dominance, Codominance, and ABO Blood Types Review of Simple Mendelian Genetics Law of Segregation: each gene has two different alleles that are separated when gametes form One allele goes to one gamete and the other allele to a different gamete Law of Independent Assortment: genes for different traits are inherited independently from each other Review of Simple Mendelian Genetics Dominant vs. Recessive alleles for a gene The dominant allele masks the recessive one, so you see the dominant trait (for RR or Rr) The only way to see a recessive trait is to have two recessive alleles (rr) Dominant allele is represented as a capital letter (R) Recessive allele is represented as a lowercase letter (r) Unfortunately, it’s not all that easy… Incomplete Dominance Sometimes neither allele is fully dominant over the other Incomplete Dominance: neither allele is dominant but combine and display a new trait that is a mixing of the two alleles Incomplete Dominance RR R’R’ RR’ RR’ RR RR’ R’R’ Incomplete Dominance In incomplete dominance, the two alleles are represented as Two capital letters When these two alleles come together, they portray a mixing of the two phenotypes! Codominance Other times both alleles are fully dominant Codominance: both alleles of a gene are dominant and the heterozygous phenotype has both traits equally expressed Codominance x BB WW BW Codominance In codominance the two alleles are represented as Two capital letters: Use the first letter of one trait (B for Brown) and the first letter of the other trait (W for White) When they come together as a heterozygote, both traits show as the phenotype Let’s Stop and Think… Let’s say there are two alleles for the hair color trait- red and blue What would be the resulting phenotype of a heterozygous pair if the alleles showed incomplete dominance? A.
    [Show full text]
  • Module 2: Genetics
    Genetics Module B, Anchor 3 Key Concepts: - An individual’s characteristics are determines by factors that are passed from one parental generation to the next. - During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene. - Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses. - The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. - Mendel’s principles of heredity, observed through patterns of inheritance, form the basis of modern genetics. - Some alleles are neither dominant nor recessive. Many genes exist in several different forms and are therefore said to have multiple alleles. Many traits are produced by the interaction of several genes. - Environmental conditions can affect gene expression and influence genetically determined traits. - The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell. - DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. - DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. - Replication in most prokaryotic cells starts from a single point and proceeds in both directions until the entire chromosome is copied. - In eukaryotic cells, replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied. - The main differences between DNA and RNA are that (1) the sugar in RNA is ribose instead of deoxyribose; (2) RNA is generally single-stranded, not double-stranded; and (3) RNA contains uracil in place of thymine.
    [Show full text]
  • Male Dominance Rarely Skews the Frequency Distribution of Y Chromosome Haplotypes in Human Populations
    Male dominance rarely skews the frequency distribution of Y chromosome haplotypes in human populations J. Stephen Lansing*†, Joseph C. Watkins‡§, Brian Hallmark*, Murray P. Cox†¶, Tatiana M. Karafet¶, Herawati Sudoyoʈ, and Michael F. Hammer¶ Departments of *Anthropology and ‡Mathematics, and ¶Division of Biotechnology, Biological Sciences West, University of Arizona, Tucson, AZ 85721; †Santa Fe Institute, Santa Fe, NM 87521; and ʈThe Eijkman Institute for Molecular Biology, Diponegoro 69, Jakarta 10430, Indonesia Edited by Simon A. Levin, Princeton University, Princeton, NJ, and approved June 3, 2008 (received for review October 25, 2007) A central tenet of evolutionary social science holds that behaviors, such as those associated with social dominance, produce fitness effects that are subject to cultural selection. However, evidence for such selection is inconclusive because it is based on short-term statistical associations between behavior and fertility. Here, we show that the evolutionary effects of dominance at the population level can be detected using noncoding regions of DNA. Highly variable polymorphisms on the nonrecombining portion of the Y chromosome can be used to trace lines of descent from a common Fig. 1. Population models. Colored dots represent individuals who have male ancestor. Thus, it is possible to test for the persistence of descendants in the final generation. Red dots represent dominant individuals differential fertility among patrilines. We examine haplotype dis- who are more likely to reproduce. Pink dots represent nondominant individ- tributions defined by 12 short tandem repeats in a sample of 1269 uals having a dominant ancestor. Blue dots represent nondominant individ- men from 41 Indonesian communities and test for departures from uals having no dominant ancestor.
    [Show full text]
  • Treatment of Particular Topics. Thus Markert Illustrates Some of the Done
    REVIEWS 333 MENDELCENTENARY: GENETICS, DEVELOPMENT AND EVOLUTION (Proceedings of a Symposium held at the Catholic University of America, November 3rd, 1965). Edited by Roland M. Nardone. The Catholic University of America Press, Washington. pp. 174+v. Thismemorial volume, published rather belatedly nearly three years after the event, contains seven short essays and a translation (the same one as in Bateson's Mendel's Principles of Heredity) of Mendel's famous paper. The essays are mostly aimed at a non-specialist audience, but some of them will be interesting to professional geneticists by virtue of their detailed treatment of particular topics. Thus Markert illustrates some of the problems and ideas concerning the regulation of gene activity in higher organisms by reference to lactate dehydrogenase isozymes and Bolton discusses the determination of homologies between DNA of different species using hybridisation techniques. Both these contributions are profusely illustrated (all the speaker's slides seem to have been reproduced) and are sufficiently detailed to be useful references, though much more has been done on DNA hybridisation since 1965. Among other contributors, Davidson discusses the use of numerical scores based on multiple characters in the disentanglement of difficult taxonomic groups, and Dorothea Bennett uses the Tailless series of alleles in the mouse to show how the analysis of the developmental basis of genetic abnormalities can aid understanding of normal development. Lewontin's essay on the gene and evolution presents ideas rather than information. It contains a thoughtful and thought-provoking assessment of the genetic and physiological advantages of the diploid way of life. Nardone's summary of molecular biology in relation to the origin of life seems, in contrast, rather elementary and second-hand, though it may have been correctly judged for the audience.
    [Show full text]
  • Showing Dominance for a Certain Character with Individuals from an Unrelated Population
    GENETICAL CONTROL OF PENETRANCE AND EVOLUTION OF DOMINANCE IN DROSOPHILA M. J. WHIUEN* Department of Botany, University of Tasmania Received13.x.67 1. INTRODUCTION IT is well established that the degree of dominance a character maintains over its allelomorph often depends on the genotype as a whole (for review see Dobzhansky, 1951, p. 104; and Goldschmidt, 1938, p. 107) and there is considerable evidence that genes modifying dominance exist in a variety of organisms, e.g. cotton, mice, Drosophila, Lepidoptera and poultry, etc. Furthermore, the experiments by Ford (1940) on the dominance of yellow ground colour in the Currant Moth Abraxas grossulariata, and by Fisher and Holt (1944) on the Sd (short-tail) gene in mice, demonstrate how rapidly dominance relationships can be reversed under artificial selection. Evidence of an evolutionary nature on dominance modification has been obtained for several species by crossing individuals from a population showing dominance for a certain character with individuals from an unrelated population. If a breakdown in dominance occurs through outcrossing it is attributed to the introduction of an alien background. It is supposed that the highly selected background necessary for dominance to be maintained increased the effect of the major gene so that the same phenotype is produced by either one or two doses of the gene. Removal or disruption of this background by outcrossing destroys the dominance relationships which have evolved. The breakdown of dominance by outcrossing has been demonstrated in cotton (Harland and Attek, 1941), in the Lesser Yellow-underwing Moth Triphaena comes (Ford, 1964, p. 125), in the genus Papilio (Clarke and Sheppard, 1960, 1963) and in Biston betularia by Kettlewell (Ford, 1964, p.
    [Show full text]
  • Ch 14-15 Review Questions
    Genetics II Answered Review Questions 1. Explain the incomplete dominance inheritance pattern. “Alleles can show different degrees of dominance and recessiveness in relation to each other. We refer to this range as the spectrum of dominance. One extreme on this spectrum is seen in the F1 offspring of Mendel’s classic pea crosses. These F1 plants always looked like one of the two parental varieties because of the complete dominance of one allele over another. In this situation, the phenotypes of the heterozygote and the dominant homozygote are indistinguishable.” “The alleles for some characters fall in the middle of the spectrum of dominance. In this case, the F1 hybrids have a phenotype somewhere in between the phenotypes of the two parental varieties. This phenomenon, called the incomplete dominance of either allele, is seen when red snapdragons are crossed with white snapdragons: All the F1 hybrids have pink flowers (see figure below). This third phenotype results from flowers of the heterozygotes having less red pigment than the red homozygotes (unlike the situation in Mendel’s pea plants, where the Pp heterozygotes make enough pigment for the flowers to be a purple color indistinguishable from those of PP plants).” (Text quoted from page 260 of the textbook) With incomplete dominance, there is no dominant and recessive trait. As a result, there are three different phenotypes. The ratio for two hybrids parents would be 50% like the parents, 25 % with one homozygous trait expressed and 25% with the other homozygous trait expressed. Looking at snapdragon flower color, if both parents had a pink flower, we would expect 50% of their offspring to have the pink color flower (heterozygous pink), 25% would be expected to have a red color (homozygous red) and we would expect 25% to have the white flower color (homozygous white).
    [Show full text]