2Gregor MendelModern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peasused experimental methodused quantitative analysiscollected data & counted themexcellent example of scientific methodHe studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery.The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.
3Mendel’s work Bred pea plants P F1 F2 Pollen transferred from white flower to stigma of purple flowerBred pea plantscross-pollinate true breeding parents (P)P = parentalraised seed & then observed traits (F1)F = filialallowed offspring to self-pollinate & observed next generation (F2)Panthersremovedall purple flowers resultF1P = parentsF = filial generationself-pollinateF2
5Looking closer at Mendel’s work true-breedingpurple-flower peastrue-breedingwhite-flower peasXPWhere didthe white flowers go?100%F1generation(hybrids)purple-flower peasIn a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation.White flowers came back!self-pollinateF2generation3:175%purple-flower peas25%white-flower peas
6What did Mendel’s findings mean? Traits come in alternative versionspurple vs. white flower colorallelesdifferent alleles vary in the sequence of nucleotides at the specific locus of a genesome difference in sequence of A, T, C, Gpurple-flower allele & white-flower allele are two DNA variations at flower-color locusdifferent versions of gene at same location on homologous chromosomes
7Traits are inherited as discrete units For each characteristic, an organism inherits 2 alleles, 1 from each parentdiploid organisminherits 2 sets of chromosomes, 1 from each parenthomologous chromosomeslike having 2 editions of encyclopediaEncyclopedia BritannicaEncyclopedia AmericanaWhat are the advantages of being diploid?
8What did Mendel’s findings mean? Some traits mask otherspurple & white flower colors are separate traits that do not blendpurple x white ≠ light purplepurple masked whitedominant allelefunctional proteinmasks other allelesrecessive alleleallele makes a malfunctioning proteinI’ll speak for both of us!wild type allele producing functional proteinmutant allele producing malfunctioning proteinhomologous chromosomes
9Genotype vs. phenotypeDifference between how an organism “looks” & its geneticsphenotypedescription of an organism’s traitthe “physical”genotypedescription of an organism’s genetic makeupF1PXpurplewhiteall purpleExplain Mendel’s results using…dominant & recessive…phenotype & genotype
10PP pp Pp Making crosses x Can represent alleles as letters flower color alleles P or ptrue-breeding purple-flower peas PPtrue-breeding white-flower peas ppF1PXpurplewhiteall purplePPxppPp
11Looking closer at Mendel’s work true-breedingpurple-flower peastrue-breedingwhite-flower peasXphenotypePPPppgenotype100%F1generation(hybrids)purple-flower peasIn a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties.The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation.PpPpPpPpself-pollinate75%purple-flower peas25%white-flower peas3:1F2generation????
12phenotype & genotype can have different ratios Punnett squaresAaaaah,phenotype & genotype can have different ratiosPp x PpF1generation(hybrids)%genotype%phenotypePpmale / spermPP25%75%Pp50%Ppfemale / eggsPPPpPpPppp25%25%pp1:2:13:1
13Genotypes Homozygous = same alleles = PP, pp Heterozygous = different alleles = Pphomozygous dominantheterozygoushomozygous recessive
14Can’t tell by lookin’ at ya! Phenotype vs. genotype2 organisms can have the same phenotype but have different genotypeshomozygous dominantPPpurplePpheterozygouspurpleCan’t tell by lookin’ at ya!How do you determine the genotype of an individual with with a dominant phenotype?
15Test crossBreed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allelexHow does that work?is it PP or Pp?pp
16How does a Test cross work? xxAm I this?Or am I this?PPppPpppppppPPPpPpPpPpPpPpPppppp100% purple50% purple:50% white or 1:1
17Mendel’s 1st law of heredity PPPLaw of segregationduring meiosis, alleles segregatehomologous chromosomes separateeach allele for a trait is packaged into a separate gametepppPpPp
18Whoa! And Mendel didn’t even know DNA or genes existed! Law of SegregationWhich stage of meiosis creates the law of segregation?Metaphase 1Whoa! And Mendel didn’t even know DNA or genes existed!
19Monohybrid crossSome of Mendel’s experiments followed the inheritance of single charactersflower colorseed colormonohybrid crosses
20Mendel was working out many of the genetic rules! Dihybrid crossOther of Mendel’s experiments followed the inheritance of 2 different charactersseed color and seed shapedihybrid crossesMendel was working out many of the genetic rules!
21Dihybrid cross P YYRR yyrr 100% F1 YyRr 9:3:3:1 F2 x true-breeding yellow, round peastrue-breedinggreen, wrinkled peasxYYRRyyrrY = yellowR = roundy = greenr = wrinkled100%F1generation(hybrids)yellow, round peasYyRrWrinkled seeds in pea plants with two copies of the recessive allele are due to the accumulation of monosaccharides and excess water in seeds because of the lack of a key enzyme. The seeds wrinkle when they dry.Both homozygous dominants and heterozygotes produce enough enzyme to convert all the monosaccharides into starch and form smooth seeds when they dry.self-pollinate9:3:3:1F2generation9/16yellowroundpeas3/16greenroundpeas3/16yellowwrinkledpeas1/16greenwrinkledpeas
22Which system explains the data? What’s going on here?If genes are on different chromosomes…how do they assort in the gametes?together or independently?YyRrIs it this?Or this?YyRrYRyrYRYryRyrWhich system explains the data?
23 Is this the way it works? YyRr x YyRr YR yr YR YYRR YyRr yr YyRr 9/16yellowroundYRyr3/16greenroundWell, that’s NOT right!YRYYRRYyRr3/16yellowwrinkledyrYyRryyrr1/16greenwrinkled
24 Dihybrid cross YyRr x YyRr YR Yr yR yr YR Yr yR yr YYRR YYRr YyRR orYyRrxYyRr9/16yellowroundYRYryRyrYRYryRyr3/16greenroundYYRRYYRrYyRRYyRrBINGO!YYRrYYrrYyRrYyrr3/16yellowwrinkledYyRRYyRryyRRyyRr1/16greenwrinkledYyRrYyrryyRryyrr
25Mendel’s 2nd law of heredity Can you think of an exception to this?Law of independent assortmentdifferent loci (genes) separate into gametes independentlynon-homologous chromosomes align independentlyclasses of gametes produced in equal amountsYR = Yr = yR = yronly true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequentlyyellowgreenroundwrinkledYyRrYrYryRyRYRYRyryr1:1:1:1
26Law of Independent Assortment Which stage of meiosis creates the law of independent assortment?Metaphase 1Remember Mendel didn’t even know DNA —or genes— existed!EXCEPTIONIf genes are on same chromosome & close togetherwill usually be inherited togetherrarely crossover separately“linked”
27The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspring
28Review: Mendel’s laws of heredity Law of segregationeach allele segregates into separate gametesMetaphase 1Law of independent assortmentgenes on separate chromosomes assort into gametes independentlyEXCEPTIONlinked genesmetaphase1
29Mendel chose peas wisely Pea plants are good for genetic researchavailable in many varieties with distinct heritable features with different variationsflower color, seed color, seed shape, etc.Mendel had strict control over which plants mated with whicheach pea plant has male & female structurespea plants can self-fertilizeMendel could also cross-pollinate plants: moving pollen from one plant to another
30Mendel chose peas luckily Pea plants are good for genetic researchrelatively simple geneticallymost characters are controlled by a single gene with each gene having only 2 alleles,one completely dominant over the other
331. In a cross AaBbCc AaBbCc, what is the probability of producing the genotype AABBCC? 1/41/81/161/321/64Answer: eSource: Barstow - Test Bank for Biology, Seventh Edition, Question #33
342. You are handed a “mystery’’ pea plant with long stems and axial flowers, and asked to determine its genotype as quickly as possible. You know the allele for long stems (L) is dominant to that for dwarf stems (l) and that the allele for axial flowers (A) is dominant to that for terminal flowers (a). You cross the “mystery” plant with a dwarf stemmed axial flowered plant. If your mystery plant is heterozygous at both loci, what is/are the expected proportion of offspring?100% long stemmed terminal flowered100% dwarf stemmed terminal flowered100% long stemmed axial flowered50% long stemmed axial flowered, 50% dwarf stemmed terminal flowered25% long stemmed axial flowered, 25% long stemmed terminal flowered, 25% dwarf stemmed axial flowered, 25% dwarf stemmed terminal floweredAnswer: eSource: Campbell/Reece - Biology, Seventh Edition, EOC Process of Science Question
35F. Feather color in budgies is determined by two different genes that affect the pigmentation of the outer feather and its core. Y_B_ is green; yyB_ is blue; Y_bb is yellow; and yybb is white. A green budgie is crossed with a blue budgie. Which of the following results is not possible?all green offspringall blue offspringall white offspringall yellow offspringAll of the above are possible, but with different probabilities.Answer: eSource: Barstow - Test Bank for Biology, Seventh Edition, Question #35