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Everyone was interested in inheritance during late 1800s © 2014 Pearson Education, Inc. Why was Mendel able to deduce this “particulate pattern” while others were struggling? Imagine you are interested in inheritance……. What measurements could you make on the people in this class and perhaps their parents? © 2014 Pearson Education, Inc. Fig. 1. Difference between the outcomes from blending and from particulate inheritance. In postMendelian terms, we assume a single diallelic locus, and hence three diploid genotypes (AA, blue; Aa, green; aa, yellow). Under particulate inheritance, the population's variability is preserved from generation to generation. In contrast, the conventional wisdom of Darwin's day saw offspring inherit a blend of parents' characteristics, here represented as the average of the two parental shadings. The result is Education, that theInc. variability diminishes in successive generations (the variance is halved each © 2014 Pearson He was successful because he chose …. • • • • • • • flower color is purple or white flower position is axil or terminal stem length is long or short seed shape is round or wrinkled seed color is yellow or green pod shape is inflated or constricted pod color is yellow or green He did not choose traits like • • • • • number of seeds per pod pod length pod width seeds per plant seed weight © 2014 Pearson Education, Inc. Mendel chose to track only characters that varied in an “either-or” rather than a more or less manner .. his plants had either purple or white flowers, there was nothing intermediate between these two varieties. Had Mendel focused instead on characters that vary in a continuum among individuals-seed weight for example-he would not have discovered the particulate nature of inheritance. …….Campbell © 2014 Pearson Education, Inc. Considering all that can occur in the pathway from genotype to phenotype it is indeed impressive that Mendel could simplify the complexities to reveal the fundamental principles governing transmission of individual genes from parents to offspring..… Campbell 1865 Mendel publishes his PARTICULATE VIEW of Inheritance … Almost completely ignored! © 2014 Pearson Education, Inc. Figure 11.2 Why are peas so great to work with? Technique 1 2 Parental generation (P) 3 Stamens Carpel Now what? 4 Lets zoom in! Results 5 First filial generation offspring (F1) © 2014 Pearson Education, Inc. What is particulate inheritance? Figure 11.4 Review of terms… What is a locus? What are alleles? Allele for purple flowers Locus for flower-color gene Pair of homologous chromosomes Allele for white flowers • Is this individual with these chromosomes in their cells homozygous or heterozygous? • What is the genotype? • If purple flower allele is dominant, what is the phenotype? © 2014 Pearson Education, Inc. P P Homozygous Purple X Homozygous White What will gametes look like? (What will their genotype be?) © 2014 Pearson Education, Inc. P P X What will gametes look like? © 2014 Pearson Education, Inc. All heterozygotes! They are called the F1 generation (results of first cross) What color will they be if P is dominant? © 2014 Pearson Education, Inc. Figure 11.3-3 Experiment P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers Selfor cross-pollination So all F1 are Pp-lets breed these purple F1 together (do a Pp What x Pp cross)! F2 Generation What are the genotypes of the gametes of these Pp plants? How would we do a Punnet square showing this cross? What are genotypes © 2014 Pearson Education, Inc. 705 purple-flowered 224 white-flowered and phenotypes of offspring? plants plants Figure 11.5-3 P Generation Purple flowers Appearance: PP Genetic makeup: Gametes: White flowers pp p P F1 Generation Appearance: Genetic makeup: Gametes: Purple flowers Pp ½ p ½ P F2 Generation 3 © 2014 Pearson Education, Inc. :1 Figure 11.6 3 Phenotype Genotype Purple PP (homozygous) Purple Pp (heterozygous) 1 2 1 © 2014 Pearson Education, Inc. Purple Pp (heterozygous) White pp (homozygous) Ratio 3:1 Ratio 1:2:1 1 Figure 11.3-3 Experiment P Generation (true-breeding parents) Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers Self- or cross-pollination F2 Generation 705 purple-flowered 224 white-flowered plants plants © 2014 Pearson Education, Inc. To understand Punnet squares you have to have some understanding of probability? Rr vs Rr cross Gametes for Rr individual will be….. Gametes for Rr individual will be…. What proportion of gametes in bucket will be R? r? What is probability of an RR individual in next generation? An Rr individual? An rr individual? © 2014 Pearson Education, Inc. Figure 11.9 Rr Segregation of alleles into eggs Rr Segregation of alleles into sperm × Sperm R ½ R R ½ ¼ ¼ r r r R r ¼ © 2014 Pearson Education, Inc. r R R Eggs ½ r ½ ¼ Lets add another locus-Use same logic! Imagine crossing a pea heterozygous at the loci for flower color (white-W versus purple-w) and seed color (yellow-Y versus green-y) with a second pea homozygous for flower color (white) and seed color (yellow). Gametes for first pea will be??? © 2014 Pearson Education, Inc. “heterozygous at the loci for flower color (white-W versus purple-w) and seed color (yellow-Y versus green-y)” WwYy WY Wy wY wy Lets do gametes for second individual! “second pea homozygous for flower color (white) and seed color (yellow)” WWYY Punnet square for this cross??? © 2014 Pearson Education, Inc. Some of you might notice that I assumed something in that last example. But lets move on… Next example is same idea but different traits! © 2014 Pearson Education, Inc. Figure 11.8 Experiment YYRR P Generation yyrr y Gametes YR y yr r Y Y F1 Generation R Predictions YyRr R Hypothesis of dependent assortment Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation Two traits are… Seed colorEggs ½ YR Seed texture ½ yr Sperm ½ YR ½ yr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr ¼ yr Phenotypic ratio 3:1 Gametes formed by both parents are?? YyRr Yyrr yyRr yyrr YYRR YyRr YyRr ¾ yyrr ¼ Yr Eggs ¼ yR ¼ 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Results Punnet square for this cross?? (will be boring) 315 © 2014 Pearson Education, Inc. 108 101 32 Phenotypic ratio approximately 9:3:3:1 r Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR yr F1 Generation YyRr Genotype of F1? Hypothesis of dependent assortment Predictions Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation Sperm ½ YR ½ yr ½ YR Eggs ½ yr YYRR YyRr YyRr ¾ yyrr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR ¼ Yr Eggs ¼ yR YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYRR YYRr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR F1 Generation Predictions yr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Now what will the gametes orof these individuals be? Sperm Predicted offspring in F2 generation ¼ YR ¼ Yr ¼ yR ¼ yr Sperm ½ YR ½ yr Self or cross-pollinate within the F1YYRR using a Punnett ¼ YR YYRr YyRR YyRr ½ YR square to getEggs F2… YYRR YyRr ¼ Yr ½ yr YYRr Eggs YyRr ¾ yyrr ¼ yR YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYrr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR yr F1 Generation YyRr Hypothesis of dependent assortment Predictions Sperm or Predicted offspring in F2 generation Sperm ½ YR ½ yr ½ YR Eggs ½ yr YYRR YyRr YyRr ¾ yyrr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR ¼ Yr Eggs ¼ yR YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYRR YYRr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR yr F1 Generation YyRr Hypothesis of dependent assortment Predictions Sperm or Predicted offspring in F2 generation Sperm ½ YR ½ yr ½ YR Eggs ½ yr But what if….. YYRR YyRr YyRr ¾ yyrr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR ¼ Yr Eggs ¼ yR YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYRR YYRr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment P Generation YYRR yyrr Gametes YR y r yr Y Y R F1 Generation YyRr R Predictions y r Hypothesis of dependent assortment Hypothesis of independent assortment What have I done? Sperm Gametes would be? ½ YR ½ yr ¼ YR Gametes will be…YR and yr only ½ YR YYRR YyRr ¼ Yr Eggs What would F1 genotype be? Eggs ½ yr Sperm or Predicted offspring in F2 generation YyRr yyrr ¼ YR ¼ Yr ¼ yR ¼ yr YYRR YYRr YyRR YyRr YYRr YyRr YYrr Yyrr ¼ yR YyRR YyRr yyRR yyRr (all YyRr)----is this ¾same or different than previous ¼ Y¼ yr y Y y Phenotypic ratio 3:1 YyRr Yyrr yyRr yyrr example? 9 Results 315 © 2014 Pearson Education, Inc. 108 101 32 R 3 16 16 x 3 16 1 16 Phenotypic ratio 9:3:3:1 r R r Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR y r yr Y Y R F1 Generation YyRr R Hypothesis of dependent assortment Predictions Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation ¼ YR ¼ Yr ¼ yR ¼ yr Sperm ½ YR ½ yr ½ YR Eggs ½ yr YYRR YyRr YyRr ¼ YR ¼ Yr Eggs yyrr ¼ yR ¾ ¼ Y¼ Do YyRr x YyRr Phenotypic cross…. ratio 3:1 9 What gametes will be produced? Results 315 © 2014 Pearson Education, Inc. y r 108 101 32 R yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr Y yyRr yyrr y YyRr 3 16 16 Yyrr x 3 16 1 16 Phenotypic ratio 9:3:3:1 r R y r Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YyRr x YyRr? Gametes YR yr F Generation gametes YR and yr only! Y 1 Hypothesis of dependent assortment Predictions y Y y Hypothesis of independent assortment r YyRr x R R r Sperm or Predicted offspring in F2 generation ¼ YR ¼ Yr ¼ yR ¼ yr Sperm ½ YR ½ yr ¼ YR YYRR YYRr YyRR Next generation ½(combine gametes randomly)? YR YYRR YyRr ¼ Yr Eggs Eggs ½ yr YyRr yyrr Gamete YR plus gamete YR = ¾ ¼ Gamete YR plus gamete yr = Phenotypic ratio 3:1 Gamete yr plus gamete yr = © 2014 Pearson Education, Inc. ¼ yr 9 16 YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results YYRR ¼ yR YYRr YyRr YyRr108 315 101 yyrr 32 How many genotypes? Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR yr F1 Generation YyRr Hypothesis of dependent assortment Predictions Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation Sperm ½ YR ½ yr ½ YR Eggs ½ yr YYRR YyRr YyRr ¾ yyrr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR ¼ Yr Eggs ¼ yR YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYRR YYRr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Figure 11.8 Experiment YYRR P Generation yyrr Gametes YR yr F1 Generation YyRr Hypothesis of dependent assortment Predictions Hypothesis of independent assortment Sperm or Predicted offspring in F2 generation Sperm ½ YR ½ yr ½ YR Eggs ½ yr YYRR YyRr YyRr ¾ yyrr ¼ YR ¼ Yr ¼ yR ¼ yr ¼ YR ¼ Yr Eggs ¼ yR YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr yyRr yyrr ¼ Phenotypic ratio 3:1 ¼ yr 9 16 3 16 Yyrr 3 16 1 16 Phenotypic ratio 9:3:3:1 Results 315 © 2014 Pearson Education, Inc. YYRR YYRr 108 101 32 Phenotypic ratio approximately 9:3:3:1 Getting more real….. (we will step through a bunch of more complex genetic situations-these are important) Most genes affect multiple traits! Pleiotropy! (Ex Cystic fibrosis p 217) Most real loci have many alleles! © 2014 Pearson Education, Inc. EX. Imagine a locus with four different alleles for fur color in an animal. The alleles are named Da, Db, Dc, and Dd. If you crossed two heterozygotes, DaDb and DcDd, what genotype proportions would you expect in the offspring? • • • • • 25% DaDc, 25% DaDd, 25% DbDc, 25% DbDd 50% DaDb, 50% DcDd 25% DaDa, 25% DbDb, 25% DcDc, 25% DdDdDcDd 50% DaDc, 50% DbDd 25% DaDb, 25% DcDd, 25% DcDc, 25% DdDd © 2014 Pearson Education, Inc. When a disease is said to have a multifactorial basis, it means that • it is caused by a gene with a large number of alleles. • it affects a large number of people. • it has many different symptoms. • both genetic and environmental factors contribute to the disease. • it tends to skip a generation. Come up with an example of a multifactorial disease! © 2014 Pearson Education, Inc. Figure 11.10-2 P Generation Red C RC R Gametes White CWCW CR CW Pink C RC W F1 Generation Gametes ½ CR ½ CW Today…..What is this called? Is this blending inheritance??? © 2014 Pearson Education, Inc. This chicken is heterozygous at a single locus (BW), erminette. What is going on here? What is this called? © 2014 Pearson Education, Inc. Plus many genes interact with one another…. © 2014 Pearson Education, Inc. Figure 11.12 BbEe BbEe Sperm ¼ bE ¼ BE ¼ Be ¼ be Eggs ¼ BE ¼ bE ¼ Be ¼ be BBEE BbEE BBEe BbEe BbEE bbEE BbEe bbEe BBEe BbEe BBee Bbee BbEe bbEe Bbee bbee What is this called? 9 Epistasis © 2014 Pearson Education, Inc. : 3 : 4 Traits are usually determined by many more than one or two loci! © 2014 Pearson Education, Inc. Figure 11.13 Do you think 3 loci is realistic for skin color? Sperm 1 1 1 1 1 Eggs 1 1 1 1 1 8 8 1 8 1 1 8 8 1 8 1 1 8 8 8 8 8 8 8 8 8 8 Phenotypes: Number of dark-skin alleles: © 2014 Pearson Education, Inc. AaBbCc AaBbCc 1 64 0 6 64 1 15 64 2 20 64 3 15 64 4 6 64 5 1 64 6 1 64 Human skin color is a “polygenic” trait, meaning multiple gene loci are involved in its expression. At last count, the International Federation of Pigment Cell Societies…has determined that there are a total of 378 genetic loci involved in determining skin color in humans and mice. http://www.gbhealthwatch.com/Trait-Skin-Color.php © 2014 Pearson Education, Inc.
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