1. Chapter 3Genetics: The science ofheredity Miss Luzma Fabre

2. Section 1: Mendels workGregor Mendel madeexperiments on plants thatrevolutionized the study ofheredityHeredity is the passing ofphysical characteristics fromparents to offspring 3. Each different form of a characteristic iscalled a traitEx: eye colorMendel observed plant traits such asheight and seed colorGenetics is the study of heredity 4. Mendels experiments Mendel used pea plants He developed a method by which he cross- pollinated, or crossed pea plants: he took pollen from one and brushed it into the second plant Fertilization is the process in which an egg cell and a sperm cell join to form a new organism 5. Crossing pea plantsMendel crossed plants with contrastingtraits (ex: tall and short)He started with purebred plantsA purebred organism is the offspring ofmany generations that have the sametrait 6. The F1 offspringMendel crossed purebred tall plantswith purebred short plants (P= parentalgeneration)The offspring from this cross are calledF1 generationAll the F1 plants were tall 7. The F2 offspringThe F1 generation self-pollinated,resulting in the F2 generationSome plants were tall and some shortin the F2 generationTall= plantsShort= plants 8. In all of Mendels crosses, only oneform of the trait appeared in the F1generation. However, in the F2generation, the lost form of thetrait always reappeared in about onefourth of the plants 9. Dominant and recessiveallelesA gene is the set of information that controls atrait.Alleles are the different forms of a geneAn orgnaisms traits are controlled by the allelesit inherits from its parents. Some alleles aredominant, while other alleles are recessive. 10. A dominant allele is one whose traitalways shows up in the organism whenthe allele is present. Ex: YA recessive allele is hidden wheneverthe dominant allele is present. Ex: y 11. A hybrid is an organism that has 2different alleles for a traitEx: Yy 12. A dominant allele is represented by acapital letter (Ex. T= tall)A recessive allele is represented by alowercase letter (Ex. t= short)Examples:Purebred= TT, ttHybrid= Tt 13. Mendels contributionMendels discoveries demonstrated thattraits are determined by individual,separate alleles inherited from eachparent rather than being a blend fromthe parentstraits