1. THE WORK OF GREGOR MENDEL

2. Background information... ► HEREDITY = the transmission of characteristics from one generation to the next ► GENETICS = the science which deals with the study of heredity

3. GREGOR MENDEL (1822-1884) ► Austrian Monk ► Student of both biology and mathematics ► Considered to be the “Father of Genetics” ► His conclusions have formed the foundation for much of what we understand about heredity today

4. Biologists liked Mendel’s Research Methods... ► Sound experimental design ► Simple but powerful experiments ► Hundreds of repetitions ► Meticulous record keeping ► Quantitative as well as qualitative observations ► Mathematical manipulation of numerical data (underlying patterns)

5. THE PEA PLANT... ► Much of Mendel’s success was due to his choice of the pea plant for experiments ► He used the common pea plant (Pisum sativum)

6. Why was the common pea plant so suitable for genetic experiments? An excellent choice for 4 main reasons: ► Commercially available throughout Europe ► Easy to grow & matured quickly ► Has several characteristics that express themselves as pairs of contrasting traits ► Is a self-pollinating plant (allows one to control which individuals are crossed)

7. Mendel examined 7 different traits:

8. Mendel’s First Experiment – A Monohybrid Cross ► Mendel took purebred plants and designated them as the parent generation or “P generation” ► He crossed a pure breeding tall pea plant with a pure breeding short pea plant ► The offspring from this cross were the first filial generation, or the F 1 generation ► Mendel called the F1 generation HYBRID plants to indicate they were the result of a cross between two different purebred plants ► This is called a MONOHYBRID cross because only one trait, plant height was involved

9. ► Pure breeding tall X pure breeding short ► RESULTS - F 1 Generation = All TALL ► Conclusion: The trait for tallness is DOMINANT to the trait for shortness ► This led Mendel to formulate The Principle of Dominance...

10. PRINCIPLE OF DOMINANCE ► When individuals with contrasting traits are crossed (dominant and recessive), the offspring will express only the dominant trait

11. Mendel’s Second Experiment... ► Allowed the F 1 generation to self-pollinate ► Results: F 2 generation was ¾ Tall and ¼ short ► 3:1 ratio ► Conclusions: The F 1 generation plants were hybrids (contain both traits – tallness and the trait for shortness)

12. Mendel’s Hypothesis: ► Each trait is determined by pairs of discrete physical units or factors (we now call genes) ► Pairs of genes separate from each other during gamete formation (Principle of Segregation) ► Which member of a pair of genes becomes included in a gamete is determined by chance

13. Continued... ► There may be 2 or more alternative forms of a gene (alternative forms of a gene are called alleles, 1 allele may be dominant to another allele) ► True breeding organisms have 2 of the same allele (homozygous) while hybrid have 2 different alleles (heterozygous)