Presentation on theme: "Introduction to Mendelian Genetics. Some History For thousands of years farmers and herders have been selectively breeding their plants and animals to."— Presentation transcript:
Introduction to Mendelian Genetics
Some History For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last 150 years Started with the studies of an Austrian monk = Gregor Mendel ?
Who was Gregor Mendel? He is known as the FATHER OF GENETICS He discovered how traits were inherited – the 1 st scientist to obtain successful results from inheritance studies due to his methodology Lived: 1822 – 1884 His work was unimportant until early 1900s GENETICS – study of heredity HEREDITY – the passing of traits from parents to offspring
Mendels Home & Garden
Mendels 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) =phenotypes Pea plants can be self-fertilized or cross-fertilized (cross pollinated)
Cross Pollination (1)The pollen contains the male gamete and can be picked up by a fine brush (2)The carpel is the female reproductive structure in a flower and contains the ovary where fertilization of the female gamete occurs (3)Fertilization occurs after pollen has landed (or placed) upon the carpel
Genetic Terminology 1.True-Breeding – (PURE BRED) these organisms ALWAYS create offspring that look like themselves (same phenotypes or traits) 2.Hybrids – offspring from different true- breeding organisms Tall purebred x Short prurebred = Hybrid
Ideas about traits during Mendels time Most scientists thought that traits blended in offspring to produce middle ground offspring Parent Offspring
Mendels 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).
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)
Mendels Experiments Parents = PFirst generation offspring = F1 Second generation offspring = F2 Observable trait = phenotype Genetic makeup = genotype Genotype is represented by capital and lower case letters Pure BredHybrid
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)
1.Principle of Dominance and Recessiveness One allele in a pair may mask the effect of the other 2.Principle of Segregation The two alleles for a characteristic separate during the formation of eggs and sperm 3.Principle of Independent Assortment The alleles for different characteristics are distributed to reproductive cells independently Three important conclusions to Mendels research