Genetics Part two

INHERITANCEMendel’s LawsGenetic CrossesGenetic PhenomenaMolecular GeneticsCode of Genetic InformationGENEis the code in DNA for a specific sequence of amino acids: A PROTEINMany genes in DNA moleculeGene delineated byINITIATOR CODE (TAC)TERMINATOR CODE (ATT, ATC, ACT)DNA serves as template for the formation of a “work horse” molecule:RNA(can move out of nucleus with copy of genetic code)Process of Interpreting the Genetic Code Genetic Code is TRANSCRIBEDinto mRNA moleculeTRANSLATIONof Genetic Code:mRNA molecule attaches to RIBOSOME2 codons at a time fit in ribosometRNA carries amino acids (tRNA binds to mRNA in ribosome by comeplementary base pairing) Places amino acids in correct sequence in proteinTHE WORK OF MENDELGregor Mendel was an Austrian monk who did important early work on inheritance and geneticsHe was an excellent mathematician and this helped him understand what others could not Mendel worked with common garden peasfor much of his early workMENDELMendel’s work on the genetics of peas began with observation of the peas to determine what traits were inheritedHe noticed at least 7 characteristics that appeared to be inheritedWe will work with 3 of these -plant height, pea color and pea shapePLANT HEIGHTMendel noticed that garden peas occur in at least two heights -Tall and ShortSince peas are self-pollinating, tall peas tend to produce tall peas and short produce shortMendel’s first genetic cross involved tall peas cross-pollinated with short peasPLANT HEIGHTMendel noticed that tall peas crossed with short peas yielded all tall peas in the F1 generation(first group of offspring)TALL X SHORTALL TALLPLANT HEIGHTMendel now took the F1 peas and crossed them with themselves to produce an F2 generation (2nd group of offspring)This produced tall and short offspring in a 3 tall to 1 short ratioF1 TALL X F1 TALL3 TALL : 1 SHORTMENDEL’S LAWSLaw of Unit Characters1. The factors of inheritance occur as solid particles in pairs within organismsMendel emphasized this to explain the continued presence of shortness in the F1 tall peas and to dispel the idea of “Blending Inheritance” common in his timeLaw of DOMINANCE2. Concept of Dominant Characteristicsa member of a pair of unit characters may dominate or hide the other member of the pair; dominant vs recessiveMendel proposed this to explain why all the F1 peas were tall while containing the short factor from one parentT = tall t = short peas = TtParents were TT X tt and F1LAW OF SEGREGATION3. The Law of Segregationat the time of gamete formation, members of a pair of unit characters segregate (separate) from one another and move into different gametesThus parents like this Tt and Ttmake these gametes TtTtSTEPS For WORKING A GENETICS PROBLEMAssign symbols for allelesDetermine the parents’ GENOTYPESDetermine the kinds of GAMETESLook at all possible combinations of gametes: PUNNETT SQUAREDetermine the possible offspring PHENOTYPESDoing the CrossUsing these laws we can see how Mendel got the 3 tall to 1 short ratio among the peas:T t T t gametesTtXTtparentsTT Tt Tttt offspringPunnett SquaresPunnett Squares are an organized way to show these same results in chart formIt is easier to see theGenotypes(allele combinations) and Phenotypes (appearances)T tTtT tT tTTttREALITY CHECK -Test CrossMendel checked his results by doing a cross of peas that had these genotypes: Tt XttCan you do the Punnett Square?ADDITIONAL CROSSESMendel performed other tests to verify resultsA cross for pea colors revealed that Yellowis dominant togreenin peas (Y and y)A cross for pea shape revealed that Round is dominant to wrinkled (R and r)These MONOHYBRID(one character) crosses worked well with his lawsCORN CROSSESSome of the corn crosses you observed in lab were this type of cross...The 3:1 and 1:1 ears for Purple and Yellow kernels were monohybrid crosses similar to the pea crosses just discussedWhich was dominant in these crosses ?CORN PUNNETT SQUARESHere is a Punnett Square for the corn crosses performed in labPPPpppppppppPPPPPPppppppMENDEL GETSMendel now decided to try a DIHYBRID(two character) cross involving pea color and pea shape in the same crossDIHYBRID CROSSMendel already knew from previous crosses that Round (R) was dominant to wrinkled (r)Also he knew that Yellow (Y) was dominant to green (y)Not surprisingly when he crossed peas that were always Round and Yellow with wrinkled green peas ...What did he predict of the F1 peas?All Round and Yellow ... DIHYBRID CROSSHere is the cross to produce the F1 generation...THE F2 CROSSMendel expected the F2 cross to produce a 3:1 ratio of Round Yellow Peas to wrinkled green peasThis is the way it worked in monohybrid crosses...X3 Round Yellow : 1 wrinkled greenSURPRISE !!!Mendel did NOT get what he expected He found a 9:3:3:1 ratio among four phenotypes instead of the 3:1 among two phenotypesHe found -9 round yellow 3 round green3 wrinkled yellow1 wrinkled greenLaw of Independent AssortmentThese results caused Mendel to propose another law called INDEPENDENT ASSORTMENTThis law states that at the time of reproduction the members of two or more pairs of unit characters follow the law of segregation independently of each other and assort themselves at random into the gametesIN OTHER WORDS ..If a parent has thisgenotypeThese are the GametesRY Ry rY ryRrYyTHE CROSSRY Ry rY ryRYRyrYryRRYYRRYyRrYYRrYyRRYyRRyyRrYyRryyRrYYRrYyrrYYrrYyRrYyRryyrrYyrryyNON-MENDELIAN GENETICSThis type of genetics was not discovered by Mendel so it is Non-MendelianIt is not any harder than Mendelian, but there are some twists to it that make it seem stranger than it is ....Incomplete DominanceThis was the first type of Non-Mendelian genetics to be discoveredIt involved Japanese Four o’clocksRed flowered plants always produced red when crossed with other redsWhite flowered plants always produced white when crossed with other whitesRed X White produced all Pink F1 plants and 1 Red : 2 Pinks : 1 White in F2 plantsIncomplete DominanceRed = RR and White = WW so Pink F1 = RWRW X RW to make the F2’sRR RWWWRWRW WRWMULTIPLE ALLELESGenes may have more than two alleles in this type of Non-Mendelian GeneticsExample is Human Blood TypeThere are three alleles of ABO blood type geneIor A promotes blood type AIor B promotes blood type Bior O promotes blood type OABWhat Genotypes are possible from these 3 alleles?IAIAor IAi = Type A bloodIBIBor IBi = Type B bloodIAIB= Type AB bloodii=Type O bloodHypothetically?If John has type A blood ....and Ruby has type B blood...Could Farqhar (their love child) be type O?What are the odds of this happening?1 in 4 !The SquareIAi X IBi then :IBiIAiiiIBIAi IAIBiPOLYGENIC INHERITANCEThis type of inheritance involves .....“many genes” influencing the inheritance of one trait or characteristicHuman Skin Color, Height and Intelligence are examplesExpect a “Curve of Normal Distribution” for this type of inheritancePLEIOTROPHIC INHERITANCEThis is simply the opposite of polygenic One gene influences the inheritance of many characteristics...These usually involve basic structural genes SEX-LINKED INHERITANCEGenes which occur on the sex chromosomes are said to be sex-linked because they show up exclusively or more frequently in one sexRed-green color blindness and hemophilia are examplesAre these traits more common in males of females?Which sex chromosome (X or Y) are they linked to?