Bio Sci H97 Genetics Lecture 1, 2024 PDF

Bio Sci H97 Genetics Lecture 1, September 27th 2024 Part I Mendelian genetics Read chapter 2, p31-51 (38-67) Version 8-31-22 Bio 97, Parsons, UCI - Copyright: All rights reserved  Lectur...

Bio Sci H97 Genetics Lecture 1, September 27th 2024 Part I Mendelian genetics Read chapter 2, p31-51 (38-67) Version 8-31-22 Bio 97, Parsons, UCI - Copyright: All rights reserved  Lecture 1: Learning Objectives By the end of today’s lecture, you should be able to: Appreciate the experimental conditions that allowed Mendel’s analysis Describe the consequences of Mendel’s laws of segregation and independent assortment. Recite single gene inheritance ratios Use a Punnett square to determine genotype and phenotype Predict phenotypic/genotypic ratios in crosses of parents that differ at a single gene locus. Understand how a test cross can be used to determine an unknown genotype. Predict genotypic and phenotypic ratios in independently assorting dihybrids Bio 97, Parsons, UCI - Copyright: All rights reserved  Lecture 1: Keywords Scientific Method Hypothesis Blending Theory Phenotype Genotype Pure-Breeding Dominant/Recessive Homozygous/ Allele Heterozygous Punnett Square Back cross/ test cross Mendel’s Law of Heredity Diploid/Haploid Law of Segregation Law of Independent Assortment Law of Dominance Dihybrid Cross Chi-Square P-Value Bio 97, Parsons, UCI - Copyright: All rights reserved  Prevailing idea at the time: Blending Theory o In Mendel’s time it was believed that reproduction lead to a blending of parental traits. - he opposed this because be Otherwise there would no black or white X cats left o We can call this hypothesis ‘the blending theory of heredity’ o Mendel set out to test this hypothesis using rigorous scientific methods. Bio 97, Parsons, UCI - Copyright: All rights reserved 2  Mendel’s Approach THE SCIENTIFIC METHOD 1. Start with observations 2. Formulate a testable hypothesis 3. Design an experimental test and collect data 4. Analyze the results and compare them to the predictions from the hypothesis 5. Accept or nullify the hypothesis Bio 97, Parsons, UCI - Copyright: All rights reserved 1 6  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3 1. Traits with Distinguishable Phenotypes Iphenotypes Reviewed in Reid and Ross, Genetics 189: 3-10 Bio 97, Parsons, UCI - Copyright: All rights reserved 4  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3  2. Pure-Breeding Strains & everything ishomozygous X X Bio 97, Parsons, UCI - Copyright: All rights reserved 5  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3  3. Controlled Crosses Between Plants removing anthers - This was done to stop the plants from self fertilizing ↑ Father Allows testing reciprocal chose the mother 3 crosses purposely Bio 97, Parsons, UCI - Copyright: All rights reserved 6  3. Controlled Crosses Between Plants Parental ↳ the starting point here is the -everyone pure breed F1 hybrid (filial) All progeny have purple flowers  No blending ! Purple is dominant, white is recessive The phenotypes of the F1 progeny reveal which traits are dominant Bio 97, Parsons, UCI - Copyright: All rights reserved 7  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3 What 4: happens in the next Quantification generation? of results Bio 97, Parsons, UCI - Copyright: All rights reserved 8  4: Quantification of results - recessive ↳ dominant Thethis From phenotypes in the cross, the probability thatF2 show a pea a 3:1 will grow up toratio have purple flowersisis13inin44 white flowers Bio 97, Parsons, UCI - Copyright: All rights reserved 9  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 3  5: Mendel got similar results with all 7 traits taking other pure breed phenotypes I andlyzingtheech was close to 3 :1 phenotype ratio prevalen ↑ Bio 97, Parsons, UCI - Copyright: All rights reserved 11  Blending Dominance empty o Mendel’s results did not support the ‘blending’ hypothesis o He came up with another hypothesis to fit his observations o New hypothesis – Particulate inheritance Bio 97, Parsons, UCI - Copyright: All rights reserved 12  Particulate inheritance Homozygous Homozygous dominant recessive Heterozygous Mendel did not know -about accells at the time o There are two discrete copies ofunits eachofgene - alleles heredity o One unit allelecomes comesfromfromeach eachparent. parent.Each Eachindividual individualcontributes contributesone oneunit allele to eachtoof each of its offspring its offspring o Some The actions of some units are alleles dominant areother over dominant unitsover other alleles (recessive) Bio 97, Parsons, UCI - Copyright: All rights reserved 13  Testing particulate inheritance recessive #Heterozygous Tomozygous - test cross-adds recessive something homozygous Prediction: If the two allele hypothesis is correct and R is dominant over r then the phenotype from the above test-cross is 1:1 > - Sox. Chance ! Bio 97, Parsons, UCI - Copyright: All rights reserved 14 Mendel’s Test Cross Results for F1 - I to + ratio Bio 97, Parsons, UCI - Copyright: All rights reserved 15  Experimental Innovations Mendel’s experiments were successful because of strong experimental design 1. Selection of Traits with Distinguishable Phenotypes 2. Pure-Breeding Strains 3. Controlled Crosses Between Plants 4. Quantification of Results 5. Replicate-, Reciprocal- and Test-Cross Analysis Bio 97, Parsons, UCI - Copyright: All rights reserved 16  Back crossing can be a test cross ask about this in class Bio 97, Parsons, UCI - Copyright: All rights reserved 17  What about the F2 Generation? Mendel’s hypothesis predicted that 1/3 of the F2 with the dominant phenotype would be pure breeding 2/3 of the F2 with the dominant phenotype would be heterozygous He verified this by allowing them to self fertilize and examining their progeny Y will likely be homozygous recessive Bio 97, Parsons, UCI - Copyright: All rights reserved 18 Mendel’s Results for the F2 Generation (with dominant phenotype) Bio 97, Parsons, UCI - Copyright: All rights reserved 19  Mendel’s Results and Conclusions Result: ALL F1 Progeny appear identical and resemble one parent -they don’t look ‘in-between’ Conclusion: Inheritance does not involve ‘blending’ of traits Result: When F1 are self-mated, they give rise to some progeny that resemble and some that do not resemble the F1 parents Conclusion: The F1 plants are not true-breeding – somehow they still contain the recessive trait even though they are not expressing it Result: A test cross shows that the F1 have both traits in a 1:1 ratio. Conclusion: The F1 contain just as much of the recessive trait as they do the dominant trait Bio 97, Parsons, UCI - Copyright: All rights reserved 20  Mendel’s Laws of Heredity o Traits are controlled by pairs of ‘particles of heredity’ (alleles) Phenotype is controlled by genes that have different alleles o Individuals contain two particles that segregate pollen and egg Individuals are diploid and alleles segregate into haploid gametes o The particles combine at random during fertilization Male and female gametes combine at random during fertilization. o These particles can be dominant or recessive Alleles can be dominant or recessive – the recessive phenotype is only seen in homozygotes Bio 97, Parsons, UCI - Copyright: All rights reserved 21  Mendel’s Laws of Heredity o Mendel’s Law of Segregation (First Law) During gametogenesis, the two alleles of a gene segregate from each other; each gamete has an equal probability of containing either allele. o Mendel’s Law of Independent Assortment (Second Law) The alleles of one gene sort into gametes independently of the alleles of another gene o Mendel’s Law of Dominance (Third Law) Alleles can be dominant or recessive – the recessive phenotype is only seen in homozygotes Bio 97, Parsons, UCI - Copyright: All rights reserved 22 Study Guide Define blending theory and give an example of a prediction consistent with the blending theory of inheritance. List the 5 critical experimental innovations that Mendel used and write a sentence describing each innovation. Draw a sample cross of pea plants, labeling the P, F1 and F2 generations. Draw a figure that illustrates a reciprocal cross and a test cross. Define dominant and recessive. At what generation could Mendel tell that the blending theory was incorrect? Are the pure breeding plants Mendel used in the P generation homozygous or heterozygous? Use a Punnett square to illustrate the genotypic and phenotypic ratios of one of Mendel’s crosses. Draw two Punnett squares that show the possible results of a test cross between a true breeding plant that gives yellow seeds and a plant with a yellow seed phenotype. 31  Study Guide Con’d Define dihybrid cross and draw a picture of one between two true-breeding pea plants, labeling the P and F1 generations and the genotypes of each. Define the law of independent assortment. Draw the Punnett square for a test cross between a plant that is heterozygous for two traits and a plant that is homozygous recessive at the same two traits. Write down the genotypic and phenotypic ratios. Given a calculator, a Chi squared table, be able to test a hypothesis based on Mendelian genetics 32  Peer recommended resources: Punnett square and test questions https://scienceprimer.com/punnett-square-calculator Hereditary Heredity: Crash Course Biology #9 Mendel https://youtu.be/8y_SLtToUOA dihybrid cross https://www.youtube.com/watch?v=fe5kSSs83qc Chi square https://www.bisd303.org/cms/lib3/wa01001636/centricity/domain/587/chi-squarepractice.pdf Chromosomes and Mendel’s Law https://www.youtube.com/watch?v=IShS60Azqjg 33