ZOL 141 1st Edition Lecture 9 Outline of Last Lecture II Meiosis New Gene Combinations A Random assortment B Crossing over I Formation of Gametes a Males b Females Outline of Current Lecture III Gregor Johann Mendel A Study of single traits B Experimental setup C Conclusions D Mendel s first law Current Lecture Transmission of Genes from Generation to Generation Chapter 3 Gregor Johann Mendel 1822 1884 Grew up on family s farm in Austria Had aptitude for learning Studied to be monk at St Thomas Monestary in 1843 1851 sent to University of Vienna to continue studying science studied with Frans Unger Christian Doppler 1853 returned to Monastery and experimented with pea plants that have shaped modern understanding of trait inheritance Mendel s Study of Single Traits Does each parent contribute equally to traits of offspring o Female gametes are often larger than male gametes Do traits in offspring result from a blending of parental traits or are the inherited as discrete units Experimental setup o Selecting a model organism Distinct traits that can be studied Self fertilizing Offspring should be fertile o Common pea plant o o Many varieties with different traits available Self or artificially fertilized fertile offspring Short life cycle and easily maintained Preparing for study Chose 7 traits that had two variations True breeding two years Large scale experiments 28000 pea plants Mendel s Study of Single traits experiments and results P1 parental smoothxwrinkled F1 filial smooth Only one of the parental traits was present in the F1 plants Did not matter which trait was present in the plant that contributed the pollen results were the same DIAGRAM Mendel s conclusions Traits are not blended o They remain unchanged even though they may not be expressed Each parent makes an equal contribution to genetic makeup of the offspring Self fertilized F1 plants monohybrid cross to determine if wrinkled trait was hidden in them still F2 second filial generation 3 1 ratiosmooth wrinkled Trait not present in F1 plants reappeared in 25 of F2 plants More conclusions Traits are determined by genes factors o Alternative forms of genes are called alleles Genes can be present but not expressed o Dominant trait is expressed in F1 o Recessive trait not expressed in F1 but reappears in some F2 plants Plants with smooth peas in P1 and F1 are genetically distinct o Knew this because self cross of P1 was smooth o Phenotype describes observable properties of an organism o Genotype describes specific genetic constitution of an organism Each plant carries two genes for a given trait o In case of F1 plant it must carry one allele for smooth pea shape and one allele for wrinkled shape o Uppercase dominant o Lowercase recessive o S smooth s wrinkled Members of gene pair must segregate during gamete formation o Principle of segregation Mendel s first law Mendel s first law o Equal chance either allele alleles reunite randomly o Homozygous having identical alleles for one or more genes o Heterozygous having two different alleles for one or more genes o Punnett square allows you to predict the genotypes of the offspring that result from a particular cross