2 Words to know Test cross Genotype F1 generation Phenotype P generationMonohybrid crossDihybrid crossKaryotypePunnett SquareMendel’s PrinciplesIncomplete DominanceCodominanceMultiple AllelesGenotypePhenotypeDominantRecessiveHomozygousHeterozygousGeneAlleleGene symbolGenome
3 Mendel’s 4 Principle’sInheritance of biological characteristics is determined by genesPrinciple of DominanceLaw of SegregationPrinciple of Independent Assortment
4 Mendel’s 4 PrincipalsInheritance of biological characteristics is determined by genesPrincipal of Independent AssortmentGenes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms.Principle of DominanceWhen there are two or more alleles for a gene, some are dominant while others are recessiveLaw of SegregationIn sexually reproducing organisms, adult cells have two copies of each gene—one from each parent; these genes segregate when GAMETES are formed
5 Exception to Mendel’s Principles Incomplete Dominance (blending)Red flower + white flower= pink flowerCo-DominanceChicken with black and white feathersMultiple AllelesMany different possible alleles for 1 gene (blood type)Polygenic traitsTraits controlled by many traits (eye color height)
6 From Peas and fruit flies to humans… The Human GenomeFrom Peas and fruit flies to humans…
8 What is a genome???All the genetic information (genes) that make up an organism
9 What makes us human? Analyze human chromosome… Karotype Picture of all the chromosomes in an organismAutosomesCHROMOSOMES 1-44 (pairs 1-22)Autosomal chromsomesSex chromosomesDetermine a person’s sex (male XY or female XX)Chromosome 45 and 46 (set 23)
11 2 events that lead to genetic variation Crossing overDuring prophase 1 of meiosis 1Segments of homologous chromosomes exchangedIndependent AssortmentIn metaphase 1 of meiosis 1When homologous chromosomes line up in random order along center of the cell in a random fashion
17 True breeding/Purebred Parts of the plantFemale part-pistil (egg)Male part-stamen-pollen (sperm)FertilizationProduces new cell which develops into an embryo and is enclosed by a seedSelf-pollinatingContain male and female partsSperm cell in pollen fertilizes egg cells in flowerOffspring inherit all traits of parentTrue breeding/PurebredGenetically identical organisms produced through self-pollinationAllowed to self pollinateTall plantGreen seedsCross PollinationCut off male parts of one plant so it only had eggsDusted it with pollen from a different plant
22 TermsGene: chemical factors (sections of DNA) that determine specific traitsTrait: a specific characteristic that varies from one individual to another.Allelle: different forms of a gene, that combined, determine a trait
23 Genotype:genetic make-up of an organism (the two alleles an organism has inherited from each parent for a trait)The two alleles carried on an organisms DNAPhenotype:physical characteristics or the OBSERVABLE version of the trait; the genotype will determine what phenotype organism has
25 ProgenyOffspringP1 refers to parent generationF1 refers to first batch of offspring from original parentsF2 refers to the offspring of the F1 organismsDominantAllele for trait that will be expressed no matter what the other allele is (A)RecessiveAllele for a trait that can only be expressed if dominant allele is ABSENT (a)Heterozygous phenotype will be Dominant (or codominant or incomplete dominance)Organism that has two different alleles for a traitAaHomozygous (Dominant or Recessive)Organism that has two IDENTICAL alleles for a traitaa or AA
26 Punnett Square Diagram that shows possible genotypes and phenotypes Probability
27 Test Crossused to determine whether a plant or animal is homozygous or heterozygous for a particular traitOrganism #1 with a DOMINANT phenotype and an UNKNOWN genotype (A ? ) is crossed with organism #2 who is homozygous recessive (aa)If #1 is homozygous Dominant (AA) for the trait, all offspring will be dominant for that traitIf #1 is heterozygous dominant (Aa), then some of the offspring will show the recessive phenotype for that trait
39 Punnet SquareHybridsOffspring of crossing two parents with different versions of a traitEx. Tall with Short; Purple with WhiteParents are the “P generation”Offspring are the “F1 generation/progeny”When two of the F1 plants are crossed, the offspring are referred to as the “F2 generation/progeny”
40 Ratios What is a ratio? Phenotypic ratios Genotypic ratios A comparison between multiple objectsPhenotypic ratiosCompares the number of different phenotypes for a cross# of Dominant Phenotype : # of Recessive PhenotypeGenotypic ratiosCompares the number of different genotypes for a cross3 possibilities # of DD : # of Dd : # of ddHomozygous dominant DDHeterozygous dominant DdHomozygous recessive dd
41 What are the phenotypes of the F1 generation? Probability of having a green pod?Probability of having a yellow pod?What are the genotypes for the F1 generation?What are the phenotypes of the F2 generation?What are the genotypes for the F2 generation?
42 Probability Def: The likelihood of an event happening It’s a way to predict the average outcome of a large number of eventsCANNOT predict the precise outcome of an event only the LIKELIHOOD of the eventFlip a coinWhat is the probability of getting heads?What is the probability of getting tails?If you flip a coin 3 times…
43 If you flip a coin two times, does the first flip effect what you are going to get in the second flip?No…One event does not effect another event’s probabilityIf there is a ¼ chance of having a white plant…the chances of having another white plant when crossing the plants again is still ¼What are the chances of having 2 white plants after two fertilizations?¼ x ¼ = 1/16
44 Things to keep in mind…Probability predicts the AVERAGE outcome of a LARGE number of eventsCannot predict a precise outcomeThe larger the number of events the closer you will be to getting the expected results
46 Let’s look at Pea shape and pea color Round (R) vs. wrinkled (r)Yellow (Y) vs. green (y)Remember, there are 4 possible gametesIf a parent is homozygous dominant (true-breeding dominant) for both shape and color, what will all possible gametes be?If a parent is homozygous recessive (true-breeding recessive) for both shape and color, what will all possible gametes be?
47 True breeding Round Yellow Peas Genotype (RRYY) Make a test cross of:True breeding Round Yellow PeasGenotype (RRYY)True breeding Wrinkled Green peasGenotype (rryy)ryryryryRYRYRYRY
48 What is the phenotype of the F1 offspring? What is the genotype of the F1 offspring?
49 What this first cross told us… All F1 offspring were heterozygous for seed shape (round) and seed color (yellow) RrYyThe F1 plant was made from fusing a gamete carrying RY and a gamete carrying ryWill the dominant alleles stay together or separate when making the F2 offspring?
50 Now cross these hybrid (RrYy) plants on a new 4X4 Punnett Square
52 What does the F2 cross tell us? Are there combinations of alleles that we did not see in either of the parents?This means that the alleles for seed color separated independently than the alleles for seed shapeGenes that segregate separately do NOT influence each other’s inheritance
53 Steps for Dihybrid cross Make a KeyTrait 1: heightDominant phenotype: Tall TT or Tt (ways to get it)Recessive phenotype: Short ttTrait2: colorDominant phenotype: Purple PP or PpRecessive phenotype: White ppWrite out genotypes for each parent_ _ _ _ x _ _ _ _Write Out Gametes for each Parent (use arrows)4 gametes for each parent (_ _)Make Punnett Square (16) boxesLabel parent one and write gametes along topLabel Parent 2 and write their gametes on sideFill in each box (should have 4 letters)Tally genotypesWrite out 4 possible phenotypic combinationsDominant trait 1 and dominant for trait 2:______Dominant trait 1 and recessive trait 2:_______Recessive trait 1 and Dominant trait 2:_______Recessive trait 1 and recessive trait 2:________Tally Phenotypes (should =16)Write phenotypic ratio__dd__:__dr__:__rd__:__rr__Dominant- capital letter DRecessive- lower case dHomozygous-2 of the same size letterIf its two little letters recessive ddIf its 2 big letters it is dominant DDHeterozygous-2 different size letters (capital and lowercase) DdALWAYS dominant
54 Principle of Independent Assortment Genes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms.
55 Exception to Mendel’s Principles Incomplete Dominance (blending)Red flower + white flower= pink flowerCo-DominanceChicken with black and white feathersMultiple AllelesMany different possible alleles for 1 gene (blood type)Polygenic traitsTraits controlled by many traits (eye color height)
56 Incomplete DominanceWhen red flowered (CRCR) plants were crossed with white flowered (CWCW) plants they made…pink flowers (CRCW)Which allele is dominant?neitherIncomplete dominance:Case in which one allele is not dominant over anotherThe heterozygous phenotype is somewhere between the two homozygous phenotypes
58 Codominance Both alleles contribute to the phenotype Chickens Allele for black feathers is codominant with allele for white feathersChicken looks speckled with black and white feathersNot like the blending of dominant phenotypes…BOTH dominant phenotypes show upIn humansGene for protein that controls cholesterol levels in the bloodPeople with heterozygous form make both types of protien
60 Multiple Alleles Genes for human blood type When a gene has more than two allelesNOT more than 2 alleles for a person but MORE than 2 alleles for the trait existCoat color in rabbitsA single gene for coat colorAt least 4 different allelesSimple dominance and make 4 possible coat colorsGenes for human blood type3 different alleles: IA, IB, IYou can get different genotypes:IAIAIAiIAIBIBIBIbiiiYou can get different Phenotypes:Type A (dom)Type B (dom)Type AB (dom)Type O (recessive)
65 Polygenic Traits “Poly” many “-genic” genes Traits controlled by two or more genesSeveral genes interact to produce a traitWide range of phenotypesSkin colorFour different genesFruit Fly eye colorThree genes make the reddish brown pigment
67 EpistasisWhen the expression of one gene effects the expression of another geneEx. Fur color in mice…controlled by 2 separate genesGene 1Brown fur pigment (BB or Bb) is dominant over gray fur pigment (bb)Gene 2Coat Pigment depositing geneDominant gene (CC or Cc) means fur will get pigment and this is determined by gene oneRecessive gene (cc) means that no pigment will be deposited on fur…whether the they have the gene for black or brown furThe gene for Pigment Deposition is the EPISTATIC gene because it alters the Phenotypic rationSd