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Name: _________________________ Period: ______ Date: ______________ GREGOR (JOHANN) MENDEL’S PEAS AND PARTICULATE INHERITANCE Modern views of inheritance date back to Gregor (Johann) Mendel (1822-1884), a retired Augustinian monk who practiced amateur botany in a quiet garden of his monastery. In 1866 he published a report of his breeding experiments on the garden pea plant. Only seven (7) years after Charles Darwin had set forth his Theory of Evolution via Natural Selection, Mendel’s publication remained obscure until 1900. at that time, three scientists, working independently, rediscovered Mendel’s Laws. They were Hugo deVries of Holland, Karl Correns of Germany, and Erich von Tschermak of Austria. Since then, the science of Genetics has virtually exploded in complexity. Although Mendel knew nothing of genes, chromosomes, or DNA, his Laws of Heredity provide the backbone of the modern synthetic approach to the study of Evolution. Out of Mendel’s studies came his idea of “particulate inheritance” which challenged the popular nineteenth century notion of “blending inheritance”. Blending inheritance maintained the traits passed on from the parents through sex cells are blended in the offspring. Darwin and his colleagues adhered tot his idea, assuming that offspring manifests characteristics that are intermediate between those possessed by the mother and father. This is illustrated by the analogy of mixing two colored liquids in a test tube. Mendel proposed fundamental units of inheritance called “factors” which are distinct entities that do not blend during fertilization. Thus, the offspring contained the distinct factors or particles from each parent. Mendel’s experiments with the edible pea plants are an excellent example of sound scientific method, even by today’s rigorous standards. He carefully chose the plants whose characteristics varied in discrete and measurable ways. After testing hundreds of species of garden plants, he chose the common sweet pea (Scientific name: Pisum sativum). He found that the pea plant had seven (7) observable characteristics that came in two, and only two, varieties. Seed shape was either smooth or wrinkled; seed interior was either yellow or green; seed coat, either gray or white; ripe pods were either inflated or constricted; unripe pods, either green or yellow; flowers were positioned either axially or terminally on the plant stem; and stems were either long or short. Other botanists in Mendel’s day merely described the characteristics of parent and offspring plants they had bred. Mendel meticulously recorded the number of plants possessing a given characteristic in each generation. He believed that the ratios of plant varieties in a generation of offspring would yield clues to the mechanisms of inheritance. Appropriately, he based his conclusions on large samples from his breeding experiments. Mendel was diligent in his experimental technique: he examined the characteristics of each plant individually and took the greatest care to prevent plants from uncontrolled cross-breeding and self-pollination. Thus, Mendel’s discovery of the Principle of Particulate Inheritance followed from his carefully controlled experiments. When he crossed plants producing smooth seeds with those producing wrinkled seeds, the results were always the same…smooth seeds. No plants contained both smooth and wrinkled seeds, and none of the seeds was just a little bit wrinkled. No blending had occurred. The same thing was noted for all the characters. As we shall observe on the next plate, the wrinkled seeds did reappear in later crosses. Mendel discovered that some traits were dominant and some, recessive. For his seven (7) pea plant characters, one variety was always found to be DOMINANT. In order to explain how RECESSIVE traits reappeared in later generations, Mendel proposed that factors contributed by both parents was maintained in the offspring in discreet units that could be inherited and passed on, regardless of whether they were expressed in the outward appearance of the offspring. This is Particulate Inheritance. DISCUSSION QUESTIONS: 1. Name the Augustinian monk who is given credit for his pioneering work in inheritance and is today referred to as the “Father of Genetics”: ____________________________ 2. What organism did this monk use in his breeding experiments? A. Common Name: _______________________________ B. Scientific Name: ______________________________ 3. In what year did he publish his important work…called “Experiments in Plant Hybridization”? _______________ 4. Give one possible reason WHY his book and his work went relatively “unnoticed” until about 1900:____________________________________________________________ 5. Out of Mendel’s studies came his idea of___________________ inheritance which challenged the popular 19th century notion of___________________ inheritance. 6. List the names of the three noted scientists who “rediscovered” Mendel, around 1900 ____________________ _______________________ ________________________ 7. Important to the understanding of Genetics today is the knowledge of how DNA, genes, and chromosomes work. Did Mendel know of these things? ____________ What were Mendel’s “units” of inheritance called in 1865? ___________________ 8. While studying Pisum sativum Mendel found that the pea plant had ______ (#) easily observable traits that were expressed in only ______ (#) varieties. 9. Complete the chart below by filling-in the blanks: TRAIT PHENOTYPES (varieties) Seed Shape Seed Interior Ripe Pods Unripe Pods Flower Position Stem Length Smooth Yellow White Constricted Wrinkled Gray Green Axial Long 10. Mendel was successful, (while others failed) because he… A. studied individual traits rather than the whole organism…….TRUE or FALSE B. introduced mathematics into his work (ratios)………………..TRUE or FALSE C. evaluated results obtained from large amounts of data……TRUE or FALSE Variation in Human Species: The Genetic Wheel PURPOSE: Variability is a basic characteristic of living things. Reserves of genetic variability are what natural selection acts on as a species meets changes in its environment. Human beings show variation in many traits that can often be detected easily by their appearance. Some of these traits may persist partly because natural selection is not even involved. That is, some of the traits leave no effect on survival today, at least not in any way geneticists can see. With the exception of identical twins it is highly improbable that any two people will have the same combination of genetically determined traits. The new characteristics in which you will work with here represent over 200,000 different combinations. Part I: Determination of Personal Physical Characteristics & Abilities TRAIT 1. Ability to taste Phenylthiocarbamide 2. Hitch Hiker’s Thumb 3. Mid-Digital Hair (On any finger) 4. Tongue Rolling 5. Ear Lobes 6. Dimples 7. Freckles (facial) Dominant Genotypes Taster (TT) (T-) Straight (EE) (E-) Present (MM) (M-) Roller (KK) (K-) Free (LL) (Ll) Present (PP) (P-) Present (JJ) (J-) Recessive Genotype List Your Phenotype Non-Taster (tt) Bent 45° plus (ee) Absent (mm) Non-Roller (kk) Attached (ll) Absent (pp) Absent (jj) Circle Your Genotype T- tt E- ee M- mm K- kk L- ll P- pp J- jj Discussion Questions: 1. Define Genotype: _______________________________________________ 2. Define Phenotype: ______________________________________________ 3. For the above traits, how many are you DOMINANT for? _____ Recessive? ___ 4. In what ways would a person with the #73 DIFFER in traits from a person who is the #56? ____________________________________________________ ______________________________________________________________ 5. Is there someone in the class like you with respect to the 7 traits above? Let’s say there is…list 3 additional traits that make you different from that person: ___________________ ____________________ _________________