Where are we in this course??? UNIT 1-History of life on earth! Big picture biodiversity-major lineages, Prokaryotes, Eukaryotes-Evolution of Meiosis Today we will start with UNIT 2 A. Mendel and the Gene Idea (Ch11) B. Chromosomal Basis of Inheritance (Ch12) C. Molecular Basis of Inheritance (Ch13) D. Gene Expression from Gene to Protein (Ch 14)
Everyone was interested in inheritance during late 1800s
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?
What is blending inheritance?? Imagine balls are individuals filled with paint and you mimic mating by randomly pulling them out of a bucket two by two.
Fig. 1. Difference between the outcomes from blending and from particulate inheritance. In post-mendelian 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 that the variability diminishes in successive generations (the variance is halved each generation if mating is at random) SCIENCE MAGAZINE B. MAY
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
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
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!
Figure 11.2 1 What is particulate inheritance? 3 2 Parental generation (P) 4 Why are peas so great to work with? 5 First filial generation offspring (F 1 )
Review of terms What is a locus? What are alleles? Homozygous? Heterozygous?
Figure 11.4 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?
P P X Homozygous Purple Homozygous White Imagine meiosis has occurred and that you are left with 4 gametes. What will gametes look like? (What will their genotype be?)
P P X What will gametes look like? Remember do not pay attention to colors of these chromosomes! I stole them from text.
All heterozygotes! They are called the F1 generation (results of first cross) What color will they be if P is dominant?
Pp x Pp X These Pp plants will make gametes with what genotypes? ½ are P and ½ are p ½ are P and ½ are p
Lets let these gametes randomly fertilize one another! What are chances of pulling a P gamete out? Another P gamete? etc CAN you ANSWER THIS IN FORM OF PUNNET SQUARE?
A more organized way to respond to this question of what are the genotypes going to be in the next generation is to use a Punnet Square.. Pp x Pp cross P p P p What are genotypes and phenotypes of offspring?
Figure 11.9 Rr Rr Segregation of alleles into eggs Segregation of alleles into sperm ½ R ½ r R R ½ R R r r r ½ r R r
Figure 11.3-3 Experiment P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation So all F1 are Pp (hybrids) All plants had purple flowers Self- or cross-pollination What F 2 Generation 705 purple-flowered plants 224 white-flowered plants
Figure 11.5-3 P Generation Appearance: Genetic makeup: Gametes: Purple flowers PP P White flowers pp p F 1 Generation Appearance: Genetic makeup: Gametes: ½ Purple flowers Pp P ½ p F 2 Generation 3 : 1
Figure 11.6 Phenotype Genotype Purple PP (homozygous) 1 3 Purple Pp (heterozygous) 2 Purple Pp (heterozygous) 1 White pp (homozygous) 1 Ratio 3:1 Ratio 1:2:1
Figure 11.3-3 Experiment P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) All plants had purple flowers Self- or cross-pollination F 2 Generation 705 purple-flowered plants 224 white-flowered plants
Figure 11.8 Experiment P Generation Y Y F 1 Generation R R YR Gametes yr y y r r Predictions Predicted offspring in F 2 generation Two traits are Hypothesis of dependent assortment Seed color ½ (Y=yellow, y=green) ½ ¾ Seed texture (R=round, r=wrinkly) ½ ½ YR yr or Phenotypic ratio 3:1 Hypothesis of independent assortment Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr 9 16 3 16 3 16 1 16 yyrr yr Results 315 108 101 32 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Genotype of F1? Predictions Predicted offspring in F 2 generation Hypothesis of dependent assortment ½ ½ ½ ½ ¾ YR yr or Phenotypic ratio 3:1 Hypothesis of independent assortment Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr yyrr yr Results 315 108 101 32 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Predictions Hypothesis of dependent assortment Hypothesis of independent assortment Now what will the gametes of these individuals be? Predicted or offspring in Yr yr F 2 generation ½ ½ YR Yr YyRR ½ Self or cross-pollinate YR within the F1 using a Punnett Yr Yr YYrr Yr square to get F2 ½ yr yr YyRR yyrr yyrr ¾ Phenotypic ratio 3:1 Yr yyrr yr 9 16 3 16 3 16 1 16 Results 315 108 101 32 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Predictions Hypothesis of dependent assortment Predicted offspring in F 2 generation ½ ½ ½ ½ ¾ YR yr or Phenotypic ratio 3:1 Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr yyrr yr Results 315 108 101 32 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Predictions Hypothesis of dependent assortment Predicted offspring in F 2 generation But what if.. ½ ½ ½ ½ ¾ YR yr or Phenotypic ratio 3:1 Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr yyrr yr Results 315 108 101 32 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation Y Y R F 1 Generation R Predictions What Predicted have I done? offspring in Gametes F 2 generation would be? Gametes will be YR Gametes Hypothesis of dependent assortment ½ ½ Results Phenotypic ratio 9:3:3:1 Is this F1 same or different than R previously? r R r 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 or yr ½ YR Yr and only! ½ yr What would F1 genotype be? yr ¾ Y Phenotypic ratio 3:1 all Hypothesis of independent assortment y r YR Yr Yr yr YyRR Yr YYrr Yr YyRR y y r yyrr Y Yr yyrr 9 16 3 16 3 16 1 16 x yyrr yr y
Figure 11.8 Experiment P Generation Y Y R F 1 Generation R Predictions What Predicted have I done? offspring in Gametes F 2 generation would be? Gametes will be YR Gametes Hypothesis of dependent assortment ½ ½ Results Phenotypic ratio 9:3:3:1 Is this F1 same or different than R previously? r R r 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 or yr ½ YR Yr and only ½ yr What would F1 genotype be? yr ¾ Y Phenotypic ratio 3:1 all Hypothesis of independent assortment y r YR Yr Yr yr YyRR Yr YYrr Yr YyRR y Y R y r yyrr Y Yr yyrr 9 16 3 16 3 16 1 16 x y r yyrr yr y
Figure 11.8 Experiment Y Y R P Generation F 1 Generation R Predictions Predicted offspring in F 2 generation YR Gametes Hypothesis of dependent assortment ½ ½ YR yr ¾ Do x cross. Phenotypic ratio 3:1 ½ ½ or yr Hypothesis of independent assortment Y Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR y y r y r yyrr Y Yr yyrr yyrr yr y What gametes will be produced? Results 315 108 101 32 R 9 16 3 16 3 16 1 16 r x Phenotypic ratio 9:3:3:1 R Phenotypic ratio approximately 9:3:3:1 r
Figure 11.8 Experiment x? Gametes gametes F 1 Generation and only! Predictions Predicted or offspring in Yr yr F 2 generation ½ ½ YR Yr YyRR Next generation ½ (combine gametes randomly)? YR Yr Yr YYrr Yr ½ yr yr Gamete plus gamete = YyRR yyrr yyrr ¾ Gamete plus gamete = Phenotypic ratio 3:1 Yr yyrr yr Hypothesis of dependent assortment Gamete plus gamete = Y R Hypothesis of independent assortment 9 16 3 16 3 16 1 16 Results Phenotypic ratio 9:3:3:1 YR 315 108 yr 101 32 Phenotypic How ratio many approximately genotypes? 9:3:3:1 y r x Y R y r
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Predictions Predicted offspring in F 2 generation Hypothesis of dependent assortment ½ ½ ½ ½ ¾ YR yr or Phenotypic ratio 3:1 Hypothesis of independent assortment Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr yyrr yr Results 315 108 101 32 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Figure 11.8 Experiment P Generation YR yr Gametes F 1 Generation Predictions Predicted offspring in F 2 generation Hypothesis of dependent assortment ½ ½ ½ ½ ¾ YR yr or Phenotypic ratio 3:1 Hypothesis of independent assortment Yr yr YR Yr Yr yr YyRR Yr YYrr Yr YyRR yyrr Yr yyrr yyrr yr Results 315 108 101 32 9 16 3 16 3 16 1 16 Phenotypic ratio 9:3:3:1 Phenotypic ratio approximately 9:3:3:1
Getting more real.. 1. Most real loci have many alleles! 2. Most genes affect multiple traits! Pleiotropy! (Ex Cystic fibrosis p 217)
Figure 11.10-2 P Generation Red C R C R White C W C W Gametes C R C W F 1 Generation Pink C R C W Gametes ½ C R ½ C W Today..What is this called? 3. Incomplete dominance! Is this blending inheritance???
This chicken is heterozygous at a single locus (BW), erminette. What is going on here? What is this called? 4. Codominance
Plus many genes interact with one another.
Figure 11.12 BbEe BbEe BE be Be be BE BBEE BbEE BBEe BbEe be BbEE bbee BbEe bbee Be BBEe BbEe BBee Bbee be BbEe bbee Bbee bbee 9 : 3 : 4
Figure 11.12 BbEe BbEe BE be Be be BE BBEE BbEE BBEe BbEe be BbEE bbee BbEe bbee Be BBEe BbEe BBee Bbee be BbEe bbee Bbee bbee 9 : 3 : 4
Figure 11.12 BbEe BbEe BE be Be be BE BBEE BbEE BBEe BbEe be BbEE bbee BbEe bbee Be BBEe BbEe BBee Bbee be BbEe bbee Bbee bbee 9 : 3 : 4
Figure 11.12 What is going on???? BbEe BbEe BE be Be be BE BBEE BbEE BBEe BbEe be BbEE bbee BbEe bbee Be BBEe BbEe BBee Bbee be BbEe bbee Bbee bbee 9 : 3 : 4
Figure 11.12 BbEe BbEe BE be Be be BE BBEE BbEE BBEe BbEe be BbEE bbee BbEe bbee Be BBEe BbEe BBee Bbee be BbEe bbee Bbee bbee What is this called? 5. Epistasis 9 : 3 : 4
6. Traits are usually determined by many more than one or even two loci!
Figure 11.13 With 2 loci what is maximum number of different gametes you could have? (Go back to your 1 example) 8 1 4 different gametes. 8 AaBbCc 1 1 8 8 AaBbCc Skin color Polygenic (quantitative 1 trait or multilocus trait 8 Imagine 3 loci! Phenotypes: 15 64 20 64 15 64 Number of dark-skin alleles: 0 1 2 3 4 5 6 How many genetically different gametes are 1 6 6 1 1 64 64 64 64 64
Figure 11.13 AaBbCc AaBbCc 1 1 8 8 Phenotypes: 15 64 20 64 15 64 Number of dark-skin alleles: 0 1 2 3 4 5 6 1 6 6 1 1 64 64 64 64 64
Figure 11.13 AaBbCc AaBbCc 1 1 8 8 Phenotypes: 15 64 20 64 15 64 Number of dark-skin alleles: 0 1 2 3 4 5 6 1 6 6 1 1 64 64 64 64 64
Figure 11.13 Do you think 3 loci is realistic for skin color? AaBbCc 1 1 8 8 AaBbCc Phenotypes: 15 64 20 64 15 64 Number of dark-skin alleles: 0 1 2 3 4 5 6 1 6 6 1 1 64 64 64 64 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
7. Multifactorial traits are the norm. 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!