Gregor Mendel. Genetics & The Work of Mendel. Mendel s work. Terminology. " Heritable features that vary among individuals are called characters.

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1 Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in eas which he began breeding a Genetics & The Work of Mendel He had studied at the University of Vienna from 1851 to 1853 where he was influenced by " a hysicist, Christian Doler, who encouraged eerimentation and the alication of mathematics to science " a botanist, Franz Unger, who aroused Mendel s interest in the causes of variation in lants. In the monastery, he carefully lanned eeriments He used quantitative analysis " collected data by recording the number of ea lants ehibiting traits he was interested in # ecellent eamle of scientific method Terminology " Heritable features that vary among individuals are called characters. Mendel s work " Bred ea lants E: Flower Color " Each variant for a character allowed to self-ollinate roduced only the same variety as the arent lant # E: urle or White " Breeding ea lants was advantageous for Mendel: Short time Large number of offsring Easy to ollinate manually Had characters that varied between two distinct alternatives " These are lants that when is termed a trait Cross-ollinated two different true breeding arents (), a white and a urle flower ea lant ollen transferred from white flower to stigma of urle flower Raised the resulting seeds & then observed traits in the net = F1 anthers removed all urle flowers result F1 # F stands for filial (Latin for son ) Allowed F1 offsring to selfollinate & observed net (F2) # F2 self-ollinate F2

2 Mendel collected data from the F2 for 7 ea traits Hyotheses on Heredity In the 1800s it was thought that arental traits blended together in offsring. In the Blending hyothesis, genetic material contributed by 2 arents mies like two colors of aint. roblem: Over time, oulations should all end u with uniform traits. Mendel s eeriments showed that this did not occur. Mendel s research gave suort to a articulate hyothesis of inheritance. arents ass on discrete heritable units (genes) that retain their searate identities in offsring in an undiluted form. Looking closer at Mendel s work What did Mendel s findings mean? " Traits come in alternative versions which account urle-flower eas X white-flower eas for the variations in inherited characters " urle vs. white flower color F1 (hybrids) urle-flower eas self-ollinate F2 75% urle-flower eas " There can be many alleles but each diloid Where did the white flowers go? carries two of the same tye or 2 different tyes White flowers came back 25% white-flower eas Alternative versions of a gene: alleles 3:1 3 urle flower lants for every 1 white flower lant " different alleles vary in the sequence of nucleotides at the secific locus of a gene # differ in the sequence of A, T, C, G along the DNA double heli of that gene on a chromosome urle-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene (alleles) are found at same location on homologous chromosomes

3 Traits are inherited as discrete units " For each characteristic, an organism inherits 2 alleles, 1 from each arent We are diloid organism " inherits 2 sets of chromosomes, 1 from each arent " A genetic locus with an allele is reresented twice in a diloid cell, once er homolog # 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 If two alleles at a locus differ, then the dominant allele determines the organisms aearance and the recessive allele has no noticeable effect on aearance. " urle & white flower colors are searate traits that do NOT blend # urle White light urle flowers # urle masked white dominant allele " Codes for functional rotein " Masks other alleles recessive allele " Either does not make a rotein or allele codes for a malfunctioning rotein wild tye allele roducing functional rotein I ll seak for both of us homologous chromosomes mutant allele roducing malfunctioning rotein Useful Genetic Vocabulary Homozygote: Organism that has a air of identical alleles for a character in question Heterozygote: Organism that has two different alleles for a gene in question Genotye: An organisms genetic makeu % Caital letter often designates dominant allele % Lower case letter often used to designate recessive allele Genotye vs. henotye " There eists a difference between how an organism looks & its genetics The urle lant differed genetically from the F1 urle lant henotye " descrition of an organism s trait " the hysical genotye " descrition of an organism s X genetic makeu Elain Mendel s results using dominant & recessive henotye & genotye F 1 urle all urle white

4 Genotye of Mendel s first cross Looking closer at Mendel s work " Can reresent alleles as letters " Flower color alleles or What is the genotye of urle-flower eas What is the genotye of white-flower eas F 1 urle X all urle white F1 urle flower is a hybrid F 1 (hybrids) F 2 urle-flower eas 75% urle-flower eas??? X urle-flower eas white-flower eas self-ollinate 25% white-flower eas? henotye genotye urle 3:1 unnett squares - diagrammatic device for redicting the allele comosition of offsring from a cross of individuals with known genotyes F 1 (hybrids) Female gametes / eggs Male gametes / serm Aaaaah, henotye & genotye can have different ratios % genotye 25% 50% 25% 1:2:1 % henotye 75% 25% 3:1 Genotyes " Homozygous = same alleles = & " Heterozygous = different alleles = homozygous dominant heterozygous homozygous recessive

5 henotye vs. genotye " 2 organisms can have the same henotye but have different genotyes urle urle How do you determine the genotye of an individual with with a dominant henotye? homozygous dominant 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 The genotye of a homozygous recessive is always known Is this genotye or? This genotye is definitely How does that work? Am I this? How does a Test cross work? Or am I this? 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 If homozygous dominant, eect urle If heterzygous, eect 50% urle:50% white or 1:1 By comaring what you get with what is eected, you can determine which genotye the arent flower started off with.

6 Law of Segregation " Which stage of meiosis creates the law of segregation? Monohybrid crosses " Some of Mendel s eeriments followed the inheritance of single characters Metahase 1 Whoa And Mendel didn t even know DNA or genes eisted With monobydrid crosses we saw: Mendel s 1st Law of Heredity Law of Segregation: Two alleles for the Dihybrid crosses " Other of Mendel s eeriments followed the inheritance of 2 different characters at ONCE E: Seed color and seed shae " These crosses are termed same heritable character dihybrid crosses " Individuals heterozygous segregate (searate) for two characters are called dihybrids # E: Genotye during gamete formation and end u in different gametes E: ONLY flower color or ONLY seed color " Such crossed are called monohybrid crosses " F1 rogeny heterozygous for a character are called monohybrids # E: Genotye Mendel was working out many of the genetic rules

7 Dihybrid cross F 1 (hybrids), eas Y = YR R = yr, eas, eas y = r = FYI Dominant alleles do not interact hysically with a recessive allele in a heterozygote, subduing the recessive allele. Alleles on homologous chromosomes are indeendent of one another. F 2 9/16 eas eas self-ollinate eas 1/16 eas henotyic ratio 9:3:3:1 In this F1 the reason why Yellow is considered the dominant allele is because it causes the henotye we see. What s going on here? Is this the way it works? or " If different genes are on different chromosomes How do they assort in the gametes? Yr yr " together or indeendently? Observed Is it this? Or this? 9/16 Which system elains the data? YR Well, that s NOT right Yr yr yr Eected 1/16

8 Yr yr Dihybrid cross Yr yr YR Yr YyRR Yr YYrr Yr YyRR yyrr yyrr "Eected Yr yyrr yr or BINGO Yr yr Observed 9/16 1/16 Mendel s 2 nd law of heredity Can you think of an ecetion to this? " Law of indeendent assortment Each air of alleles segregates indeendently of each other air of alleles during gamete formation 1 # different genes searate into gametes indeendently " non-homologous chromosomes (tetrads) align indeendently during metahase I of meiosis " classes of gametes roduced in equal amounts # = Yr = yr = " ***only true for genes on searate chromosomes or on same chromosome AND so far aart that crossing over haens frequently Yr Yr yr yr : 1 : 1 : 1 Law of Indeendent Assortment " Which stage of meiosis creates the law of indeendent assortment? Remember Mendel didn t even know DNA or genes eisted Metahase 1 EXCETION: " If genes are on same chromosome & close together " will usually be inherited together " rarely crossover searately " Genes considered linked The chromosomal basis of Mendel s laws Trace the genetic events through meiosis, gamete formation & fertilization to offsring

9 Review: Mendel s laws of heredity " Law of segregation " ea lants are good for genetic research monohybrid cross " single trait each allele segregates into searate gametes (homologous chromosomes which carry genes that may differ slightly in version searate) " established by Metahase 1 " Law of indeendent assortment Mendel chose eas wisely " flower color, seed color, seed shae, etc. dihybrid (or more) cross " 2 or more traits Distant genes on searate chromosomes (or far aart on same chromosome) assort into gametes indeendently " established by Metahase 1 EXCETION " linked genes metahase1 available in many varieties with distinct heritable features with different variations 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 Any Questions?? relatively simle genetically " most characters are controlled by a single gene with each gene having only 2 alleles, # one comletely dominant over the other