Gene Allele Genotype Phenotype Homozygous Heterozygous
GeneAlleleGenotypePhenotype Sequence of DNA that codes for a particular trait.(Ex: tongue rolling) Alternative versions of a gene. (Ex: can roll tonguevs. cannot roll tongue) The combination of alleles present in anindividual’s DNA. (Ex: RR, Rr, rr) The physical characteristics resulting from thegenotype. (Ex: can or cannot roll tongue)Homozygous Genotype with two copies of the same allele for agene. (Ex: RR or rr)Heterozygous Genotype with two different alleles for a gene.(Ex: Rr)
Dominant – The allele that isRecessive – The allele that is notexpressed when the combination of expressed when the combinationalleles is heterozygousof alleles is heterozygous– Only one copy of the allele is– Two copies of the allele areneeded for the phenotype to berequired for the phenotype toexpressedbe expressed– Genotype vs. Phenotype– Genotype vs. Phenotype Homozygous dominant orheterozygous: dominant geneis expressed Heterozygous (“carrier”): geneis expressed Homozygous recessive:dominant gene is not expressed Homozygous dominant orheterozygous: recessive geneis not expressed Homozygous recessive:recessive gene is expressed “Carrier” state does not exist
Mendel’s Laws When Mendel Crosspollinated Pea plantwith different traits,only one trait seemed tobe “expressed” in thatfirst generation ofoffspring. This trait“dominated” the other. Yet, when that firstgeneration of plantswere self pollinated, onaverage, three of everyfour plants had thedominant trait, and oneof every three had theweaker or recessive trait.
Mendel’s Laws When Mendel Crosspollinated Pea plantwith different traits,only one trait seemed tobe “expressed” in thatfirst generation ofoffspring. This trait“dominated” the other. Yet, when that firstgeneration of plantswere self pollinated, onaverage, three of everyfour plants had thedominant trait, and oneof every three had theweaker or recessive trait.
Mendel’s LawsLaw of Dominance In a cross of parents that are true-breeding forcontrasting traits, only one form of the trait willappear in the next generation. All offspring from that cross will be heterozygousand express only the dominant trait RR x rr yieldsall Rr (roundseeds)
Mendel’s LawsLaw of Segregation The two alleles for a trait must separate from eachother when gametes are formed. A parent randomly passes only one allele for eachtrait to each offspring.Law of Independent Assortment Alleles for different traits are inheritedindependently of each other.
Mendel’s LawsLaw of SegregationBefore sexualreproduction duringmeiosis, the twoalleles from the parentbecome separated soeach sex cell has onlyone allele
Mendel’s LawsLaw of Independent AssortmentInheritance ofone allele doesnot affect whichother allele willbe inherited(unless thealleles are on thesamechromosome)
An Example of How Traits Pass fromParents to First Offspring Generation
ProbabilityProbability How likely it is that something will happen Note: It does not tell you what will definitelyhappen, but only the chances that something will.
How do we determine Probability?Determining Probability Determine the number of times a specific event canoccur in relation to the total number of events that canoccur: Example: What is the probability of flipping acoin on heads? Number of specific events (heads) 1 Total number of events that can occur (headsor tails) 2 Answer: The probability is ½ or 50% chance oflanding on heads (1:1 heads to tails ratio)
Types of Genetic Crosses Monohybrid Cross Cross involving a single trait Ex: Flower color Dihybrid Cross Cross involving two traits Ex: Flower color and plant heightcopyright cmassengale13
Generation “Gap”Parental P1 Generation The parental generation in a breeding experiment.F1 GenerationF2 Generation The first-generation offspring The second-generationin a breeding experiment(1st filial generation) From breeding individualsfrom the P1 generationoffspring in a breedingexperiment (2nd filialgeneration) From breeding individualsfrom the F1 generation
The gene combinationsthat might result from agenetic cross can bedetermined by drawinga diagram known as aPunnett Square. Punnett Squarescan be used tocompare thegenetic variationsthat will result froma cross.
A capital letterrepresents thedominant allelefor tall. A lowercaseletter representsthe recessiveallele for short. In this example:– T tall– t short
Gametes producedby each F1 parentare shown alongthe top and leftside. Possible genecombinations forthe F2 offspringappear in the fourboxes.
Probability:Measure of the likelihood of an event happening.Punnett Square:A chart designed to show the probability each possiblegenotype in offspring based on parental genotypes.Determine all the possible gametes that canbe formed from each parental genotype.Mother (AABb)ABAbFather (AaBb)ABAbaBab
Parental (P) Generation:Ex: Dd (mother) x Dd (father)POSSIBLEGAMETES:DdMother dHeterozygous(Carrier)HomozygousRecessiveDdDFather (Dd)Ddd
True-breeding Green DragonsPopulation consistentlyproduces only green offspring.True-breeding Red DragonsPopulation consistentlyproduces only red offspring.
True-breedingRed (RR) ParentRR True-breeding Green(GG) ParentGGRGRedRGRedRGRedRGRed100% of offspring areRED.So RED is dominantover GREEN.
Red (R?) ParentR? Green (rr) ParentrrRrRedRrRed?r?rGreen Green50% of offspring are RED, and50% are GREEN.Since there are GREENoffspring, the RED dragon mustbe heterozygous (Rr) & doescarry the green allele.
P Generation:Father (Cc)CarrierP Generation:Father (CC)NormalMother (cc)Cystic 1 Offspring:100% CarriersP Generation:Mother (Cc)CarrierXCcCCCNormalCcCarriercCcCarrierccC.F.F1 Offspring:25% Normal, 50% Carriers25% Cystic FibrosisFather (Cc)CarrierP Generation:Father (Cc)CarrierMother 1 Offspring:25% Normal & 50% CarriersMother (cc)Cystic FibrosisXccCCcCarrierCcCarriercccC.F.ccC.F.F1 Offspring:50% Carriers50% Cystic Fibrosis
P Generation:Father (CC)NormalCCMother (cc)Cystic FibrosisXccCcCcCarrierCarrierCcCcCarrierCarrierF1 Offspring:100% Carriers
P Generation:Father (Cc)CarrierCcMother (Cc)CarrierXCcCCCcNormalCarrierCcccCarrierC.F.F1 Offspring:25% Normal, 50% Carriers25% Cystic Fibrosis
P Generation:Father (Cc)CarrierCcMother (CC)NormalXCCCCCCNormalNormalCcCcCarrierCarrierF1 Offspring:50% Normal, 50% Carriers
P Generation:Father (Cc)CarrierCcMother (cc)Cystic FibrosisXccCcCcCarrierCarrierccccC.F.C.F.F1 Offspring:50% Carriers & 50% Cystic Fibrosis
Punnett Square: A chart designed to show the probability each possible genotype in offspring based on parental genotypes. Determine all the possible gametes that can be formed from each parental genotype. AB Ab aB AB Mother (AABb) Father (AaBb) ab Ab
Created by LABScI at Stanford 2 In standard Mendelian genetics, the heterozygous condition (e.g. Aa) retains the homozygous dominant phenotype because the dominant allele masks the phenotype of the recessive allele. An example of this in humans would be a heterozygote for brown eye
3. What would the offspring genotype and phenotype probabilities be when a wrinkled seed crossed with another wrinkle seed. 4. What would the offspring genotype and phenotype probabilities be when two homozygous plants were crossed. One plant was tall and one was short.
Use Punnett square to predict the results of genetic crosses: monohybrid & dihybrid (ratio & probability). (HS10-LS3-2.1) Determine genotype and phenotype of a parent organism: heterozygous, homozygous. (HS10-LS3-2.2) Determine genotype and phenotype of an offspring
this genotype is caused by more than one gene because there are 4 phenotypes not 3 in F2 (9:3:3:1) Ð1 gene F2 would have 3 phenotypes 1:2:1 ratio Complementary Gene Action : one good copy of each gene is needed for expression of the final phenotype Ð9:7 ratio Epistasis : one gene can mask the effect of another gene
to its phenotype. It is reasonable to assume that the rela-tionship between the genotype and the phenotype is strongly causal [24], and therefore small variations on the genotype space imply small variations on the phenotype space. Since the neighborhood structure under a strongly causal mapping is conserved,
A.Allele b was lost from Population 1 because of Population 1’s large size. B.Allele B became fixed in Population 1 as a result of genetic drift. C.Allele B was maintained in Population 1 and Population 2 because of gene flow between the populations. D.Allele b conferred a selective disadvantage to finches in both populations during the study period. .
and dominance hierarchy for each gene on a separate sheet of paper as you progress. For example, crest is a recessive phenotype that requires two ‘crest’ alleles. Before they begin a puzzle, encourage students to think about the allele combination (genotype) that will yield the desired phenotype.
A WIZARD-OF-OZ EXPERIMENT TO DEMONSTRATE WATER REDUCTION AND USER TRAINING WITH AN "AUTONOMOUS" FAUCET William Jou Stanford University Stanford, CA, USA
