Division Ave. High School AP Biology

Transcription

1 Genetics & The Work of Mendel Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in eas u used exerimental method u used quantitative analysis collected data & counted them u excellent examle of scientific method Mendel s work Bred ea lants u cross-ollinate true breeding arents () = arental u raised seed & then observed traits ( ) F = filial u allowed offsring to self-ollinate & observed next (F 2 ) ollen transferred from white flower to stigma of urle flower all urle flowers result F 2 self-ollinate anthers removed 1

2 Mendel collected data for 7 ea traits Looking closer at Mendel s work urle-flower eas X white-flower eas (hybrids) F 2 75% urle-flower eas 100% urle-flower eas White flowers came back! 25% white-flower eas self-ollinate Where did the white flowers go? 100% 3:1 What did Mendel s findings mean? Traits come in alternative versions u urle vs. white flower color u alleles different alleles vary in the sequence of nucleotides at the secific locus of a gene w 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 chromosomes 2

3 Traits are inherited as discrete units For each characteristic, an organism inherits 2 alleles, 1 from each arent u diloid organism inherits 2 sets of chromosomes, 1 from each arent homologous chromosomes like having 2 editions of encycloedia w Encycloedia Britannica w Encycloedia Americana What are the advantages of being diloid? What did Mendel s findings mean? Some traits mask others u urle & white flower colors are searate traits that do not blend urle x white light urle urle masked white u dominant allele functional rotein masks other alleles u recessive allele allele makes a malfunctioning rotein wild tye allele roducing functional rotein I ll seak for both of us! homologous chromosomes mutant allele roducing malfunctioning rotein Genotye vs. henotye Difference between how an organism looks & its genetics u henotye descrition of an organism s trait the hysical u genotye descrition of an organism s genetic makeu X Exlain Mendel s results using dominant & recessive henotye & genotye urle white all urle 3

4 Making crosses Can reresent alleles as letters u flower color alleles or u urle-flower eas u white-flower eas X x urle white all urle Looking closer at Mendel s work urle-flower eas X white-flower eas henotye (hybrids) F 2 75% urle-flower eas?? 100% urle-flower eas? self-ollinate 25% white-flower eas? genotye 100% 3:1 unnett squares x (hybrids) female / eggs male / serm Aaaaah, henotye & genotye can have different ratios % genotye 25% 50% 25% % henotye 75% 25% 1:2:1 3:1 4

5 Genotyes Homozygous = same alleles =, Heterozygous = different alleles = homozygous dominant heterozygous homozygous recessive 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 How does that work? is it or? 5

6 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 u during meiosis, alleles segregate homologous chromosomes searate u each allele for a trait is ackaged into a searate gamete Law of Segregation Which stage of meiosis creates the law of segregation? Whoa! And Mendel didn t even know DNA or genes existed! Metahase 1 6

7 Monohybrid cross Some of Mendel s exeriments followed the inheritance of single characters u flower color u seed color u monohybrid crosses Dihybrid cross Other of Mendel s exeriments followed the inheritance of 2 different characters u seed color and seed shae u dihybrid crosses Mendel was working out many of the genetic rules! Dihybrid cross x, eas YYRR Y = R = yr, eas y = r = (hybrids), eas 100% F 2 9/16 eas eas self-ollinate eas 1/16 eas 9:3:3:1 7

8 What s going on here? If genes are on different chromosomes u how do they assort in the gametes? u together or indeendently? Is it this? Or this? YR YR Yr yr Which system exlains the data? Is this the way it works? YR YR YR Well, that s 7NOT right! yr x YR YYRR or Yr yr 9/16 1/16 Dihybrid cross x YR YR Yr yr or YR Yr yr 9/16 YR Yr yr YYRR YYRr YyRR 3BINGO! YYRr YYrr Yr YyRR yyrr yyrr Yr yyrr yr 1/16 8

9 Mendel s 2 nd law of heredity Can you think of an excetion to this? Law of indeendent assortment u different loci (genes) searate into gametes indeendently non-homologous chromosomes align indeendently classes of gametes roduced in equal amounts w 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 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 The chromosomal basis of Mendel s laws Trace the genetic events through meiosis, gamete formation & fertilization to offsring 9

10 Review: Mendel s laws of heredity Law of segregation u monohybrid cross single trait u each allele segregates into searate gametes established by Metahase 1 Law of indeendent assortment u dihybrid (or more) cross 2 or more traits u genes on searate chromosomes assort into gametes indeendently established by Metahase 1 EXCETION linked genes metahase1 Mendel chose eas wisely ea lants are good for genetic research u available in many varieties with distinct heritable features with different variations flower color, seed color, seed shae, etc. u Mendel had strict control over which lants mated with which each ea lant has male & female structures ea lants can self-fertilize Mendel could also cross-ollinate lants: moving ollen from one lant to another Mendel chose eas luckily ea lants are good for genetic research u relatively simle genetically most characters are controlled by a single gene with each gene having only 2 alleles, w one comletely dominant over the other 10

11 Any Questions??