Biol 423L Laboratories in Genetics Rules Cell phones off Computers only for class related work No food or drink in lab room Text Book Hartwell et al Genetics from Genes to Genomes third edition Web page www bio unc edu courses 2009Fall Biol423L Goals for course Reinforce basic genetic principles Introduce model organisms commonly used by geneticists Learn how genetics is used to understand Disease Biochemical pathways Development Lab reports Abstract Introduction Results Discussion Course information page has instructions about preparing your lab reports Grading Lab Reports 50 of grade 5 of that is participation 1 day late 50 off more than that will only be graded under special circumstances Research Paper 10 of grade Topics due Oct 13 Outline due Oct 27 Paper due Nov 24 Midterm 15 of final grade Oct 26 Final exam 25 of final grade comprehensive Dec 14 Genes Alleles and Epistasis Genetics starts with observation Observe variability Use genetics patterns of inheritance to understand the cause of the variability What proteins or RNAs are responsible for the variability you can see Easy example flower color How many genes affect flower color How variable are the proteins encoded by those genes What is the pathway to make flower color List of terms Trait some aspect of an organism that can be observed measured Phenotype the way a trait appears in an individual the combination of genotype and environment Genotype the constitution of alleles at any gene in an individual Gene continuous stretch of DNA sufficient to encode a messenger RNA or a functional RNA Locus A region of a chromosome usually for a single gene Messenger RNA the RNA message for a single protein Allele a variant of the sequence of a given gene Diploid an individual with two copies of each chromosome Haploid an individual with one copy of each chromosome How many genes affect flower color First make sure the types are heritable and true breeding homozygous for flower color alleles purple by purple self All uniform X Homozygous a diploid individual with two copies of the same allele for a given gene Heterozygous a diploid individual with two different alleles for a given gene What are the relationships between color types X purple is dominant to white Alleles are distributed as discrete units X Purple W W White A wa wa F1 W wa Punnet square helps to predict genotypes and phenotypes of the next generation Two distinct alleles at the same locus X F1 W wa F1 W wa 1 W W 2 W wa 1 wa wa 3 purple 1 white Female gametes Male gametes W wa W W W W wa wa W wa wa wa How many genes are required to make purple pigment in flowers Complementation tests can be made between recessive alleles If plants with recessive alleles are crossed and the progeny also have the recessive trait The alleles are variants of the same gene If plants with recessive alleles are crossed and the progeny have the dominant trait The alleles are variants of different genes A dominant allele cannot be used Why Allelism test 1 Cross different white flowered plants If the mutations are in the same gene The progeny will be white X white A wa wa white B wb wb F1 wa wb Complementation test double check F2 generation Cross white F1 to another white F1 If the mutations are alleles of the same gene what is the next generation wa wb X wa wb 1 wa wa 2 wa wb 1 wb wb Allelism test 2 Cross different white flowered plants If the mutations are in different genes the progeny will be pigmented X white A wa wa Wc Wc white C Wa Wa wc wc F1 Wa wa Wc wc Conclusions Wa and wa are alleles of the same gene wa and wc are alleles of different genes The dominant allele of wa and the dominant allele of wc are needed for purple color to be produced Therefore at least 2 gene products are needed to produce purple pigment To avoid confusion let s call Wa and wa R and r and wc p with a dominant allele P Allelism test Cross different white flowered plants If the mutations are in different genes The progeny will be pigmented X white A r r P P white C R R p p F1 R r P p white C purple X white A rrPP RRpp RrPp Pathway to purple Precursor 1 R or P Intermediate R or P Purple Complementation test double check The discrete alleles of two different genes Will assort randomly in future generations X white A r r P P white B R R p p F1 R r P p Punnet Square Predict the genotypes and phenotypes in the F2 generation when the trait is controlled by two genes with randomly segregating alleles F2 after RrPp X RrPp Male gametes Female gametes Rp RP RP RRPP Rp RRPp rP RrPP RRPp RRpp RrPp rP RrPP RrPp rrPP rp RrPp Rrpp rrPp 9R P 3R pp 3rrP 1rrpp Phenotypes if both R and P needed for purple color 9 purple and 7 white rp RrPp Rrpp rrPp rrpp Using multiple allelism tests with diverse recessive mutants We can identify all the genes specifically involved in making the purple pigment Predict the genotypes and phenotypes in the F2 generation when the traits are independent Eg petal color and leaf size Punnet Square Predict the genotypes and phenotypes in the F2 generation when the traits are independent Eg petal color and leaf size RrPp X RrPp Male gametes Female gametes Rp RP rP rp RP RRPP RRPp RrPP RrPp Rp RRPp RRpp RrPp Rrpp rP RrPP RrPp rrPP rrPp rp RrPp Rrpp rrPp rrpp 9R P 3R pp 3rrP 1rrpp Phenotypes if R and P affect independent traits Eg petal color and leaf size R is purple rr is white P is long leaf and pp is short leaf 9 purple long 3 white long 3 purple short 1 white short Calculate ratios with more loci probability of RR or Rr is 3 4 probability of rr is 1 4 3 loci all dominant X X all recessive X X one dominant and two recessive X X Ad infinitum Chi square test for goodness of fit Null hypothesis the alleles that control petal color and leaf size represent two different genes segregating independently Does the data fit your model n 2 Oi Ei 2 Ei i 1 n is the number of types of observations ie the number of different phenotypic classes Degrees of freedom n 1 p is probability that the null hypothesis is correct When the observations are similar to the expected values 2 is a small number and p is close to 1 0 X2 values for different degrees of freedom and the probabilities associated with the X2 values Mendel s Laws Mendel s First Law the law of segregation during gamete formation each member of the allelic pair separates from the other member to form the genetic constitution of the gamete Mendel s Second Law the law of independent assortment this says that for two characteristics the …