Chapter 12 Lecture and Reading Note taking Template 1 Early Work 2 Mendel s Work a What is meant by true breeding strains That offspring produced from self fertilization remained uniform from one generation to the next a Chose to study pea plants because Other research showed that pea hybrids could be produced Many pea varieties were available Peas are small plants and easy to grow Peas can self fertilize or be cross fertilized b Why were peas a good scientific model for Mendels work c What is meant by i Self fertilization ii Cross fertilization d Understand Fig 12 3 on how Mendel conducted his experiments 1 Produce true breeding strains for each trait 2 Cross fertilize true breeding strains having alternate forms of a trait 3 Allow the hybrid offspring to self fertilize for several generations 3 Monohybrid crosses The principle of segregation a Define i Monohybrid cross 1 cross to study only 2 variations of a single trait 2 Mendel produced true breeding pea strains for 7 different traits a Each trait had 2 variants ii Dominant expressed iii Recessive hidden by dominant allele iv F1 generation 1 Offspring produced by crossing 2 true breeding strains 2 All Mendel s F1 plants resembled only 1 parent a No plants with intermediate characteristics v F2 generation 1 Offspring from the self fertilization of F1 plants 2 Although hidden in the F1 generation the recessive trait had reappeared among some F2 individuals 3 Counted proportions of traits a Always 3 1 vi Alleles alternative form of a gene vii Heterozygous different alleles viii Homozygous 2 of the same allele ix Genotype total set of alleles think of genes x Phenotype physical appearance think of physical xi Principle of Segregation 1 Two alleles for a gene segregate during gamete formations and are joined at random during fertilization Chapter 12 Lecture and Reading Note taking Template 2 Physical basis for allele segregation is the behavior of chromosomes during meiosis xii Punnett Square predict outcomes xiii Pedigree analysis used to track inheritance patterns in families 1 Dominant pedigree juvenile glaucoma a Dominant trait appears in every generation b Describe Mendel s 5 step model describing the nature of heredity i Parents transmit discrete factors genes ii Each individual receives one copy of a gene from each parent iii Not all copies of a gene are identical iv Alleles remain discrete no blending v Presence of allele does not guarantee expression c Be able to use Punnett Squares to predict the outcome of monohybrid crosses Fig d Be able to interpret a pedigree to predict outcomes and infer genotype of family e Be able to look at a pedigree and determine if the trait is recessive or dominant Fig 12 6 members Fig 12 7 and 12 8 12 7 vs 12 8 4 Dihybrid Cross a What is a dihybrid cross i Exam 2 separate traits in a single cross b Explain what is meant by traits in a dihybrid cross behave independently i Chromosomes assort independently into each of the gametes 2 genes on different chromosomes behave independently c What is the predicted outcome of a cross of two heterozygotes for two traits Fig 12 9 d How does the Principle of Independent Assortment explain dihybrid results 5 Testcrosses Fig 12 10 a What is a testcross b Why when are they used i Reveal unknown genotypes of an individual with dominant phenotype 6 Extensions to Mendel Know Table 12 2 the exceptions to Mendel s model and examples 12 6 1 Polygenic inheritance 2 Pleiotropy Occurs when multiple genes are involved in controlling the phenotype of a trait These traits show continuous variation and are referred to as quantitative traits Refers to an allele which has more than one affect on the phenotype Pleiotropic effects are difficult to predict because a gene that affects one trait often performs other unknown functions Chapter 12 Lecture and Reading Note taking Template This can be seen in human diseases such as CF or sickle cell anemia 3 Multiple alleles for one gene More than 2 alleles for a gene in a population 3 alleles 2 are dominant AB and 1 is recessive i each individual can only have 2 alleles 4 Incomplete Dominance Heterozygotes is intermediate in phenotype between the 2 homozygotes 1 Codominance a Heterozygote shows some aspect of the phenotypes of both homozygotes 5 Environmental factors Diet Nutrition Sun on skin color Coat color in Himalayan rabbits and Siamese cats 7 Epistasis gene interactions Interactions of gene products affect predicted ratios a b Crossed of 2 white varieties of corn i F1 was all purple ii F2 was 9 purple 7 white not expected iii 2 genes interact to produce purple grain color if both not present no pigmentation 8 Human ABO blood group demonstrates a Multiple alleles i 3 alleles of the I gene b Codominance i IA and IB are dominant to i but codominant to each other See separate file posted in D2L for practice genetics problems