Gregor Mendel When two heterozygous plants are crossed the expected and observed phenotypic ratio will always be 3:1 This was the same for all 7 of his tests
Gregor Mendel Mendel concluded that the two alleles for each characteristic separate during gamete production. This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis Known as the law of segregation
Gregor MendelGenotype of alleles: R = red flower r = orange flowerAll genes occur in pairs, so 2 alleles affect acharacteristicPossible combinations are:Genotypes RR Rr rrPhenotypes RED RED ORANGE
PracticeFor each genotype: heterozygous (He) or homozygous (Ho) HoTT_____ He Bb______ Ho DD______ He Ff ______ Ho tt _____ HeDd_____ Ho ff ______ He Tt ______ Ho BB______ Ho dd_____Which of the genotypes would be purebred? TT, ff, DD, BB, tt, dd__________________________________________________Which of the genotypes would be hybrid? Dd, Bb, Tt, Ff__________________________________________________
PracticeDetermine the phenotype for each genotype Yellow body color is dominant to blue Yellow Yellow BlueYY_______________ Yy _______________yy _______________ Square shape is dominant to round Square Square RoundSS________________Ss_______________ ss________________
PracticeFor each phenotype, give the possible genotypes A tall head (T) is dominant to short (t) TT, TtTall_______________ tt Short_______________ Pink body color (P) is dominant to yellow (p) PP, PpPink_______________ pp Yellow______________
Genetic Crosses Monohybrid cross: cross involving a single trait Flower color, plant height Dihybrid cross: cross involving two traits Flower color & plant height Punnett squares help determine the possible combinations of genotypes that can occur in the offspring. It also shows the probability of each genotype occurring
Genetic CrossesSolving Punnett squares only takes a few steps:1. Determine the genotypes of the parent organisms2. Write down your ‘cross’3. Draw your Punnett square4. ‘Split’ the letters of the genotype for each parent & put them ‘outside’ the Punnett square5. Determine the possible genotypes of the offspring by filling in the Punnett square6. Summarize the results (both genotype and phenotype of the offspring)
Genetic Crosses1. Sometimes the question already tells you, other times you need to understand the vocabulary. Read carefully!2. Write down the genotypes of the parents Ex: Tt x tt3. Draw the Punnett square
Genetic Crosses4. Split the letters of our cross Tt x tt This ‘split’ represents the process of meiosis The vertical represents the male gamete The horizontal represents the female gamete
Genetic Crosses5. Each box represents a possible genotype of the offspring
Genetic Crosses6. Summarize the results of the offspring; both genotype and phenotype Genotype: 50% TT 50% tt Phenotype: 50% tall 50% short
PracticeSpongeBob is heterozygous for his square shape, butSpongeSusie is round. Create a Punnett square to show thepossibilities if they had children. (look at old questions!) Ss ss Cross: ___________ x ___________Punnett Square ____ s ____ s S ____ Ss Ss ____ s Ss ss Genotypes: Ss, ss Genotypic ratio: 3:1 Phenotypes: Square, Round Phenotypic ratio: 3:1
PracticePatrick met Patti at a dance. They are both heterozygous fortheir pink body color, create a Punnett square to show thepossibilities if they had children. (look at old questions!) Pp Pp Cross: ___________ x ___________Punnett Square ____ P ____ p P ____ PP Pp ____ p Pp pp Genotypes: PP, Pp, pp Genotypic ratio: 1:2:1 Phenotypes: Pink, yellow Phenotypic ratio: 3:1
Gregor Mendel In one dihybrid cross, Mendel studied the inheritance of seed color and seed shape The allele for yellow seeds (Y) is dominant to the allele for green seeds (y). The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r).
Gregor Mendel He crossed true-breeding plants that has yellow, round seeds (YYRR) with true-breeding plant that had green, wrinkled seeds (yyrr) One possibility is that the two characteristics are transmitted from parents to offspring as a package The Y and R alleles and the y and r alleles stay together
Gregor Mendel The Y and R alleles and the y and r alleles stay together This was not consistent with Mendel’s results
Gregor Mendel An alternative hypothesis is that the two alleles segregate independently of each other Known as the law of independent assortment The presence of one specific allele for one trait has no impact in the presence of a specific allele for the second trait.
Gregor Mendel In our example, the F1 offspring would still produce yellow, round seeds. (YyRr) However, when the F1’s produced gametes, genes would be packaged into gametes with all possible allelic combinations. Four classes of gametes (YR, Yr, yR, and yr) would be produced in equal amounts.