2 Some History?For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybridsIt was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknownKnowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last 150 yearsStarted with the studies of an Austrian monk = Gregor MendelWatch only first 45 seconds of video
3 Who was Gregor Mendel? He is known as the “FATHER OF GENETICS” He discovered how traits were inherited – the 1st scientist to obtain successful results from inheritance studies due to his methodologyLived: 1822 – 1884His work was “unimportant” until early 1900’sGregor Mendel is standing, fourth second from the rightGENETICS – study of heredityHEREDITY – the passing of traits from parents to offspring
5 Mendel’s Peas Mendel did his study on 29,000 pea plants over 14 years Pea plants have many easily observed traits (tall/short, purple flowers/white flowers)=phenotypesPea plants can be self-fertilized or cross-fertilized (cross pollinated)Mendel learned how to control the fertilization of pea plants by controlling the fertilization process. Phenotype = OBSERVABLE characteristics
6 Cross PollinationThe pollen contains the male gamete and can be “picked up” by a fine brushThe carpel is the female reproductive structure in a flower and contains the ovary where fertilization of the female gamete occursFertilization occurs after pollen has landed (or placed) upon the carpel
7 Tall purebred x Short prurebred = Hybrid Genetic TerminologyTrue-Breeding – (PURE BRED) these organisms ALWAYS create offspring that look like themselves (same phenotypes or traits)Hybrids – offspring from different true-breeding organismsTall purebred x Short prurebred = Hybrid
8 Ideas about traits during Mendel’s time Most scientists thought that traits blended in offspring to produce “middle ground” offspringParentOffspringParent
9 Mendel’s Observations & Ideas While observing many generations of pea plants, Mendel found that sometimes traits seemed to disappear for a generation and then reappear in later generations.He determined:Some factor MUST be passed from generation to generation for this to occur.(We now know these as GENES)Those traits that disappeared were recessive to other traits that were dominant.(GENES can be in different forms = ALLELES).From his observations, Mendel concluded that most traits are either dominant or recessive and do not blend in offspring.
10 Genes and Alleles Genes – factors that determine your traits Mendel determined that each trait is controlled by two factors (alleles)One from male, one from female – they can be different)
11 Genotype is represented by capital and lower case letters Mendel’s ExperimentsPure BredHybridHybrid“Mating” the plants are called “crosses”. The dominant trait is capitalized (T), while the recessive trait is lower case (t).Parents = PFirst generation offspring = F1Second generation offspring = F2Observable trait = phenotype Genetic makeup = genotypeGenotype is represented by capital and lower case letters
12 Explaining the Cross Results When a parent makes sperm or eggs, their genes separate randomly (PRINCIPLE OF SEGREGATION)The GAMETES (egg or sperm) contain either a T allele (tall) or a t allele (short)During meiosis, homologous chromosomes separate (segregate) independently
13 Since the F1 generation was ALL TALL, Mendel determined that “tall” is dominant over “short”.
15 Three important conclusions to Mendel’s researchPrinciple of Dominance and RecessivenessOne allele in a pair may mask the effect of the otherPrinciple of SegregationThe two alleles for a characteristic separate during the formation of eggs and spermPrinciple of Independent AssortmentThe alleles for different characteristics are distributed to reproductive cells independently