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Mendelian Genetics While assigned to teach, he was also assigned to tend the gardens and grow vegetables for the monks to eat. Augustinian Monk at Brno Monastery in Austria (now Czech Republic) Not a great teacher but well trained in math, statistics, probability, physics, and interested in plants and heredity. GREGOR MENDEL “FATHER OF GENETICS” Mountains with short, cool growing season pea (Pisum sativum) was an ideal crop plant. History in 1860 : • Discovered Genes as Particles of Inheritance • Discovered Patterns of Inheritance • Discovered Genes Come from Both Parents Egg + Sperm = Zygote Sperm means Seed (Homunculus) • Discovered One Form of Gene (Allele) Dominant to Another • Discovered Recessive Allele Expressed in Absence of Dominant Allele http://academic.evergreen.edu/v/vivianoc/homunculus.gif Nature vs Nurture Mendel worked with peas (Pisum sativum) • Good choice for environment of monastery • He got good varieties for testing • Pureline • Scientists of 1860s could not understand math • His work lost in journals for 50 years! • Rediscovered in 1900s independently by 3 scientists “rediscovered" in 1900, Hugo de Vries, Carl Correns, and Erich von Tschermak, and were initially very controversial. The “rediscovery” were combined with chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. One Example of Mendel’s Work P Tall DD x Dwarf dd Homozygous Dominant Phenotype Genotype Homozygous Recessive All Tall Dd F1 Clearly Tall is Inherited… What happened to Dwarf? Heterozygous F1 x F1 = F2 Punnett Square: F2 possible gametes 1. Tall is dominant to Dwarf 2. Use D/d rather than T/t for symbolic logic possible gametes D d D Tall DD Tall Dd d Tall Dd Dwarf dd 3/ Tall 1/ Dwarf 4 4 Dwarf is not missing…just masked as “recessive” in a diploid state… there IS a female contribution. Mendel as a Scientist Punnett Square: Test Cross: Unknown Tall If Unknown is x D D possible gametes d d Tall Dd Tall Dd Tall Dd Tall Dd possible gametes If Unknown is Dd: possible gametes Dwarf dd possible gametes DD: possible gametes F1 x F1 = F2 F2 d d D Tall Dd Tall Dd d Dwarf dd Dwarf dd possible gametes D d D Tall DD Tall Dd d Tall Dd Dwarf dd Test Progeny All Tall 1/ 3 of F2 Tall are DD 2/ 3 of F2 Tall are Dd Test Progeny Half Tall Half Dwarf Another Example of Mendel’s Work P Green gg x Yellow GG Homozygous Recessive Homozygous Dominant All Yellow Gg F1 Heterozygous Clearly Yellow is Inherited… What happened to Green? 1. Yellow is dominant to Green 2. Use G/g rather than Y/y for symbolic logic F1 x F1 = F2 Punnett Square: F2 possible Phenotype Genotype possible gametes NEVER use G/Y or g/y G g G Yellow GG Yellow Gg 3/ g Yellow Gg Green gg Green is not missing…just masked as “recessive” in diploid state gametes Yellow 1/ Green 4 4 Mendel as a Scientist Punnett Square: Test Cross: Unknown Yellow x G G possible gametes g g Yellow Gg Yellow Gg Yellow Gg Yellow Gg possible gametes If Unknown is Gg: possible gametes Green gg possible gametes If Unknown is GG: possible gametes F1 x F1 = F2 F2 G g g g Yellow Gg Yellow Gg Green gg Green gg possible gametes G g G Yellow GG Yellow Gg g Yellow Gg Green gg Test Progeny All Yellow 1/ 3 of F2 Yellow are GG 2/ 3 of F2 Yellow are Gg Test Progeny Half Yellow Half Green Law of Segregation (The "First Law") The Law of Segregation states that when any individual produces gametes, the copies of a gene separate, so that each gamete receives only one copy. A gamete will receive one allele or the other. The direct proof of this was later found when the process of meiosis came to be known. In meiosis the paternal and maternal chromosomes get separated and the alleles with the characters are segregated into two different Law of Independent Assortment (The "Second Law") The Law of Independent Assortment, also known as "Inheritance Law", states that alleles of different genes assort independently of one another during gamete formation. While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio between dominant and recessive phenotypes, his experiments with mixing two traits (dihybrid cross) showed 9:3:3:1 ratios . But the 9:3:3:1 table shows that each of the two genes are independently inherited with a 3:1 ratio. Mendel was success with his experiment because he was lucky, the genes were not located in the same chromosome. What would happen if the genes were in the same chromosome? Will be continued next week 1. 2. 3. 4. 5. Apriem Aria Chandra Raka Sutrisno 6. Indah 7. Bondan +
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