Mendel s work. AP Biology. Genetics & The Work of Mendel. What did Mendel s findings mean? Looking closer at Mendel s work

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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 used eerimental method used quantitative analysis collected data & counted them ecellent eamle 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 & observed net ( ) ollen transferred from white flower to stigma of flower all flowers result anthers removed Mendel collected data for 7 ea traits Looking closer at Mendel s work 75% Where did the white flowers go White flowers came back! 3:1 What did Mendel s findings mean Traits come in alternative versions 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 -flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes 1

2 female / eggs 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 like having 2 editions of encycloedia Encycloedia Britannica Encycloedia Americana What are the advantages of being diloid What did Mendel s findings mean Some traits mask others & white flower colors are searate traits that do not blend white light masked white dominant allele functional rotein wild tye allele roducing masks other alleles functional rotein recessive allele allele makes a malfunctioning 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 henotye descrition of an organism s trait the hysical genotye descrition of an organism s genetic makeu Elain Mendel s results using dominant & recessive henotye & genotye all white Making crosses Can reresent alleles as letters flower color alleles or all white Looking closer at Mendel s work 75% henotye genotye 3:1 unnett squares male / serm Aaaaah, henotye & genotye can have different ratios % genotye 50% 1:2:1 % henotye 75% 3:1 2

3 Genotyes Homozygous = same alleles =, Heterozygous = different alleles = henotye vs. genotye 2 organisms can have the same henotye but have different genotyes homozygous dominant homozygous dominant heterozygous Can t tell by lookin at ya! heterozygous homozygous recessive How do you determine the genotye of an individual with with a dominant henotye Test cross Breed the dominant henotye the unknown genotye with a homozygous recessive () to determine the identity of the unknown allele How does that work Am I this How does a Test cross work Or am I this is it or 50% :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 Whoa! And Mendel didn t even know DNA or genes eisted! Metahase 1 3

4 Monohybrid cross Some of Mendel s eeriments followed the inheritance of single characters flower color seed color monohybrid crosses Dihybrid cross Other of Mendel s eeriments followed the inheritance of 2 different characters seed color and seed shae dihybrid crosses Mendel was working out many of the genetic rules!, eas Y = R = Dihybrid cross YR yr, eas y = r = What s going on here If genes are on different chromosomes how do they assort in the gametes together or indeendently, eas Is it this Or this 9/16 eas eas eas 1/16 eas 9:3:3:1 Which system elains the data Is this the way it works or Dihybrid cross or YR yr Well, that s NOT right! 9/16 1/16 YR YR Yr YR yr yr yr yr BINGO! 9/16 1/16 4

5 Mendel s 2 nd law of heredity 1 Can you think of an ecetion to this Law of indeendent assortment different loci (genes) searate into gametes indeendently non-homologous chromosomes align indeendently classes of gametes roduced in equal amounts = = = only true for genes on searate chromosomes or on same chromosome but so far aart that crossing over haens frequently : 1 : 1 : 1 Law of Indeendent Assortment Which stage of meiosis creates the law of indeendent assortment Remember Metahase 1 Mendel didn t even know DNA or genes eisted! ECETION 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 Review: Mendel s laws of heredity Law of segregation monohybrid cross single trait each allele segregates into searate gametes established by Metahase 1 Law of indeendent assortment dihybrid (or more) cross 2 or more traits genes on searate chromosomes assort into gametes indeendently established by Metahase 1 ECETION linked genes metahase1 Mendel chose eas wisely ea lants are good for genetic research available in many varieties with distinct heritable features with different variations flower color, seed color, seed shae, etc. 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 relatively simle genetically most characters are controlled by a single gene with each gene having only 2 alleles, one comletely dominant over the other 5

6 Any Questions