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BISC403 Genetic and Evolutionary Biology Summary of basic points of Mendelian Genetics Most of this information was presented in class. My assumption is that the very large majority of students in this class are familiar with the fundamentals of Mendel’s experiments and his proposed model, probably from both high school and BISC207 experience. I am interested in using class time efficiently and have decided not to start at the very beginning. However, I am also concerned about providing appropriate guidance and not leaving people behind. Therefore, I have prepared this summary to make as clear as I can which concepts I consider essential as the starting point for this course. As I have stressed in lecture, working through the problems I identified for you will be very valuable in consolidating your knowledge of and ability to work with this information. Note that the answers to most of the oddnumbered problems are in the back of the book, just before the glossary and index. Key terms with brief comments: Self-fertilization Cross-fertilization Pure-breeding lines (note use of "strain", "biovar", and "breed" as alternatives to "lines") Hybrids Dominant and recessive traits Phenotype obser ved char acter istic Genotype infor mation that br ings about the phenotype (often with str ong influence from environmental factors) Alleles - basic units of information transmitted by each parent to the zygote. The alleles combine to form the genotype and the genotype determines what the phenotype will be. Homozygous and heterozygous ter ms to indicate if the genotype has two identical (homozygous) alleles or two different ones (heterozygous) Monohybrid cross exper iment consider ing only one featur e at a time Dihybrid cross exper iment consider ing two featur es together Test cross key pr ocedur e to deduce genotype These terms and princples are illustrated with various figures in Chapter 2. Study these figures along with the terms above in the appropriate place: Fig 2.7 Pea reproduction, Mendels’s key contribution (controlled crossing) Fig 2.8 Pea traits Mendel studied Fig 2.9 Monohybrid cross Fig 2.11 Punnett Square. This is essentially a bookkeeping process to follow the transmission and combination of all alleles) Fig 2.12 and 2.13 Genotype-phenotype relation Fig 2.14 and 2.18 Test cross, monhybrid and dihybrid, respectively. Be sure to understand these figures thoroughly. Fig 2.15 Dihybrid cross Other important points: Mendel placed great emphasis on organizing his results in terms of ratios. It is good to be familiar with the basic genotype and phenotype ratios that are observed in monohybrid and dihybrid crosses of traits that display complete dominance. This is the only kind of trait that Mendel studied although we will consider alternative situations in the near future. The following table is the simplest summary of these results showing the ratios in the F2 generation ("F2" means "second filial generation" where "filial" means "child" or "offspring"). Study these results until it is completely clear why the numbers are as they are. Memorizing the numbers is not very important; being able to derive them and most importantly being able to explain where they come from are very important Genotype ratios Phenotype ratios Monohybrid Cross 1:2:1 3:1 Dihybrid Cross 1:2:1:2:4:2:1:2:1 9:3:3:1 The book has small, detailed features (called "boxes" in other books) that offer extensions of the basic material in a more specific way than the text. Two that are important with respect to the Mendelian results are presented in Figure A and Figure B on pages 20 and 21. These examples give modern interpretation and uses for Mendel’s ideas. Read these and learn the material just as though it were part of the text. Finally, the chapter ends with a very nice extension of these concepts to human applications, especially the procedure called pedigree analysis. Read and understand the material on pages 31-35. You will need to be familiar with analyzing pedigrees and quite possibly in drawing them.