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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert.

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Presentation on theme: "LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert."— Presentation transcript:

1 LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Mendel and the Gene Idea Chapter 14

2 Overview: Drawing from the Deck of Genes The blending hypothesis –genetic material from the two parents blends together The particulate hypothesis –parents pass on discrete heritable units –Traits reappear after several generations Mendel used experiments with garden peas

3 Figure 14.1

4 Concept 14.1: Mendel identified two laws of inheritance Discovered the basic principles of heredity by breeding garden peas

5 Mendels Experimental, Quantitative Approach Advantages of pea plants for genetic study There are many varieties of heritable features(characters) Character variants (Traits) Controlled Mating Individual sex organs Cross-pollination

6 Figure 14.2 Parental generation (P) Stamens Carpel First filial generation offspring (F 1 ) TECHNIQUE RESULTS 32145

7 What Mendel Used Mendel chose to track only those characters that occurred in two distinct alternative forms True-breeding (plants that produce offspring of the same variety when they self-pollinate)

8 Terms of the Experiment Hybridization: mating two contrasting, true- breeding varieties P generation: true-breeding parents F 1 generation: hybrid offspring of the P generation F 2 generation: F 1 individuals self-pollinate or cross- pollinate with other F 1 hybrids

9 The Law of Segregation Crossing contrasting true-breeding white and purple pea plants: all of the F 1 hybrids were purple Crossing the F 1 hybrids: many of the F 2 plants had purple flowers, but some had white Three to one ratio purple to white flowers in the F 2 generation

10 Figure 14.3-3 P Generation EXPERIMENT (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants

11 Ideas that stemmed from observations Only the purple flower factor was affecting flower color in the F 1 hybrids purple flower color: dominant trait white flower color: recessive trait Six other pea plant characters had same patterns Heritable factor: we now call a gene


13 Mendels Model Alternative versions of genes: account for variations in inherited characters Alternative versions of a gene are now called alleles Each gene resides at a specific locus

14 Figure 14.4 Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes

15 Mendels Model Organisms inherits two alleles, one from each parent Dominant alleles determine the organisms appearance Recessive alleles have no noticeable effect on appearance Law of segregation: two alleles for a heritable character separate during gamete formation

16 Punnett Square Diagram for predicting the results of a genetic cross between individuals of known genetic makeup A capital letter represents a dominant allele A lowercase letter represents a recessive allele

17 Figure 14.5-3 P Generation F 1 Generation F 2 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Sperm from F 1 ( Pp ) plant Pp PP pp P P P P p p p p Eggs from F 1 ( Pp ) plant PP pp Pp 1/21/2 1/21/2 3 : 1

18 Useful Genetic Vocabulary Homozygous: An organism with two identical alleles for a character Heterozygous: An organism that has two different alleles for a gene –Unlike homozygotes, heterozygotes are not true-breeding Phenotype: physical appearance Genotype: genetic makeup

19 Phenotype Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) pp (homozygous) Figure 14.6

20 The Testcross How can we tell the genotype of an individual with the dominant phenotype? Could be either homozygous dominant or heterozygous

21 Figure 14.7 Dominant phenotype, unknown genotype: PP or Pp ? Recessive phenotype, known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Eggs or All offspring purple 1 / 2 offspring purple and 1 / 2 offspring white Pp pp p ppp P P P p TECHNIQUE RESULTS

22 The Law of Independent Assortment Followed a single character Monohybrids: individuals that are heterozygous for one character A cross between such heterozygotes is called a monohybrid cross Dihybrids: Two true-breeding parents differing in two characters produces A dihybrid cross, a cross between F 1 dihybrids

23 Figure 14.8 P Generation F 1 Generation Predictions Gametes EXPERIMENT RESULTS YYRR yyrr yr YR YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predicted offspring of F 2 generation Sperm or Eggs Phenotypic ratio 3:1 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1 315 108 101 32 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 9 / 16 3 / 16 1 / 16 YR yr 1/41/4 3/43/4 Yr yR YYRR YyRr yyrr YYRRYYRrYyRR YyRr YYRrYYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr YyrryyRr yyrr

24 Law of independent assortment Pairs of alleles segregate independently of each other pair of alleles during gamete formation

25 Figure 14.9 Segregation of alleles into eggs Segregation of alleles into sperm Sperm Eggs 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 1/41/4 1/41/4 1/41/4 Rr R R R R R R r r r r r r

26 The Multiplication and Addition Rules Applied to Monohybrid Crosses probability that two or more independent events will occur together is the product of their individual probabilities Each gamete has a ½ chance of carrying the dominant allele and a ½ chance of carrying the recessive allele

27 The addition rule Probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities The rule of addition can be used to figure out the probability that an F 2 plant from a monohybrid cross will be heterozygous rather than homozygous

28 Figure 14.UN01 Probability of YYRR Probability of YyRR 1 / 4 (probability of YY) 1 / 2 (Yy) 1 / 4 (RR) 1 / 16 1/81/8 Chance of at least two recessive traits ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr 1 / 4 (probability of pp) 1 / 2 (yy) 1 / 2 (Rr) 1 / 4 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 1 / 4 1 / 2 1 / 2 1 / 16 2 / 16 1 / 16 6 / 16 or 3 / 8

29 Extending Mendelian Genetics for a Single Gene Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: –When alleles are not completely dominant or recessive –When a gene has more than two alleles –When a gene produces multiple phenotypes

30 Degrees of Dominance Complete dominance heterozygote and dominant homozygote phenotypes are identical Incomplete dominance F 1 hybrids are somewhere between the phenotypes of the two parental varieties Codominance two dominant alleles affect the phenotype in separate, distinguishable ways

31 Figure 14.10-3 P Generation F 1 Generation F 2 Generation 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 Red White Gametes Pink Gametes Sperm Eggs CWCWCWCW CRCRCRCR CRCR CWCW CRCWCRCW CRCR CWCW CWCW CRCR CRCR CWCW CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW

32 Dominance and Phenotype A dominant allele does not subdue a recessive allele; alleles dont interact that way Alleles are simply variations in a genes nucleotide sequence Frequency of Dominant Alleles Dominant alleles are not necessarily more common 1/400 babies in the US is born with extra fingers or toes

33 Multiple Alleles Four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A, I B, and i.

34 Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O IAIA IBIB i ii IAIBIAIB I A I A or I A i I B I B or I B i

35 Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease

36 Epistasis A gene at one locus alters the phenotypic expression of a gene at a second locus Coat color of certain animals depend on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair

37 Figure 14.12 Sperm Eggs 9 : 3 : 4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 BbEe BE bE Be be BBEE BbEE BBEeBbEe BbEE bbEEBbEe bbEe BBEe BbEe BBeeBbee BbEebbEe Bbee bbee

38 Polygenic Inheritance Quantitative characters: vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance –an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance

39 Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 12345 6 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1 / 64 6 / 64 15 / 64 20 / 64 15 / 64 6 / 64 1 / 64 AaBbCc

40 The effect of environment on phenotype

41 Integrating a Mendelian View of Heredity and Variation An organisms phenotype includes its physical appearance, internal anatomy, physiology, and behavior An organisms phenotype reflects its overall genotype and unique environmental history

42 Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees

43 Figure 14.15 Key Male Female Affected male Affected female Mating Offspring 1st generation 2nd generation 3rd generation 1st generation 2nd generation 3rd generation Is a widows peak a dominant or recessive trait? (a)Is an attached earlobe a dominant or recessive trait? b) Widows peak No widows peak Attached earlobe Free earlobe FF or Ff WW or Ww Ww ww Ww ww Ff ff FF or Ff ff

44 Pedigrees Can also be used to make predictions about future offspring Can use the multiplication and addition rules to predict the probability of specific phenotypes

45 Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner These range from relatively mild to life- threatening Recessively inherited disorders show up only in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele

46 Figure 14.16 Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a

47 Dominantly Inherited Disorders Dominant alleles that cause a lethal disease are rare and arise by mutation Achondroplasia is a form of dwarfism caused by a rare dominant allele

48 Figure 14.17 Parents Dwarf Dd Sperm Eggs Dd Dwarf dd Normal Dd Dwarf dd Normal D d d d Normal dd

49 Multifactorial Disorders Heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components

50 Fetal Testing In amniocentesis, the liquid that bathes the fetus is removed and tested In chorionic villus sampling (CVS), a sample of the placenta is removed and tested Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero

51 Figure 14.19 (a) Amniocentesis (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta UterusCervix Centrifugation Fluid Fetal cells Several hours Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 11223

52 Newborn Screening Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States

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