Genetics & The Work of Mendel A 2006-2007 Biology Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in eas used exerimental method used quantitative analysis collected data & counted them excellent examle of scientific method Mendel s work Bred ea lants cross-ollinate true breeding arents () = arental raised seed & then observed traits ( ) F = filial allowed offsring to self-ollinate & observed next (F 2 ) all urle flowers result self-ollinate F 2 anthers removed 1
Mendel collected data for 7 ea traits Looking closer at Mendel s work true-breeding urle-flower eas X true-breeding white-flower eas (hybrids) 100% urle-flower eas Where did the white flowers go? 100% F 2 75% urle-flower eas White flowers came self-ollinate back! 25% white-flower eas 3:1 What did Mendel s findings mean? Traits come in alternative versions urle vs. white flower color alleles different alleles vary in the sequence of nucleotides at the secific locus of a gene some difference in sequence of A, T, C, G urle-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous A chromosomes Biology 2
Traits are inherited as discrete units For each characteristic, an organism inherits 2 alleles, 1 from each arent diloid organism inherits 2 sets of chromosomes, 1 from each arent homologous chromosomes What are the advantages of being diloid? What did Mendel s findings mean? Some traits mask others urle & white flower colors are searate traits that do not blend urle x white light urle urle masked white dominant allele functional rotein recessive allele wild tye allele roducing functional rotein I ll seak for both of us! mutant allele roducing malfunctioning rotein homologous chromosomes Genotye vs. henotye Difference between how an organism looks & its genetics henotye descrition of an organism s trait the hysical genotye descrition of an organism s genetic makeu X Exlain Mendel s results using dominant & recessive henotye & genotye urle all urle white 3
female / eggs (hybrids) unnett squares x male / serm Aaaaah, henotye & genotye can have different ratios % genotye 25% 50% % henotye 75% 25% 25% 1:2:1 3:1 henotye vs. genotye 2 organisms can have the same henotye but have different genotyes urle homozygous dominant urle How do you determine the genotye of an individual with with a dominant henotye? heterozygous Can t tell by lookin at ya! Test cross Breed the dominant henotye the unknown genotye with a homozygous recessive () to determine the identity of the unknown allele x is it or? 4
How does a Test cross work? Am I this? x Or am I this? x 100% urle 50% urle:50% white or 1:1 Mendel s 1 st law of heredity Law of segregation during meiosis, alleles segregate homologous chromosomes searate each allele for a trait is ackaged into a searate gamete Law of Segregation Which stage of meiosis creates the law of segregation? Metahase 1 Whoa! And Mendel didn t even know DNA or genes existed! 5
Monohybrid cross Some of Mendel s exeriments followed the inheritance of single characters flower color seed color monohybrid crosses Dihybrid cross Other of Mendel s exeriments followed the inheritance of 2 different characters seed color and seed shae dihybrid crosses Dihybrid cross true-breeding x, eas Y = YR R = yyrr true-breeding, eas y = r = (hybrids), eas 100% F 2 9/16 eas eas self-ollinate eas 1/16 eas 9:3:3:1 6
Is this the way it works? yr x X yr YR yyrr yr or Yr yr yr 9/16 1/16 Dihybrid cross x Yr yr yr YR Yr YyRR Yr Yr YYrr Yyrr yr YyRR yyrr yyrr yr Yyrr yyrr yyrr yr or Yr yr yr 9/16 1/16 Mendel s 2 nd law of heredity Law of indeendent assortment different loci (genes) searate into gametes indeendently non-homologous chromosomes align indeendently classes of gametes roduced in equal amounts = Yr = yr = yr only true for genes on searate chromosomes or on same chromosome but so far aart that crossing over haens frequently Yr Yr yr yr yr yr 1 : 1 : 1 : 1 7
Law of Indeendent Assortment Which stage of meiosis creates the law of indeendent assortment? Metahase 1 Remember Mendel didn t even know DNA or genes existed! EXCETION If genes are on same chromosome & close together will usually be inherited together rarely crossover searately linked 8