Presentation on theme: "Genetics Part 1: Mendelian Genetics Gregor Mendel: The “Godfather” of Genetics."— Presentation transcript:
Genetics Part 1: Mendelian Genetics Gregor Mendel: The “Godfather” of Genetics
Gregor Mendel zAustrian Monk zBorn in 1822 in what is now Czech Republic zEntered Monastery at 21 and was ordained priest four years later zMonasteries, typically, were the center of education in this time and area of the world zBecomes a teacher of science and mathematics at high school after college zAlso put in charge of monastery garden: this made him famous
Mendel’s Experiments zPlants are self-pollinators: they have both male and female reproductive organs on the same plant zMendel had purebreds (plants that only produce offspring like themselves) from eariler gardeners (these plants had self- pollinated year after year) zThese purebreds form the basis for Mendel’s work zMendel learns to cross-pollinate by cutting out male and female parts from different plants
Mendel’s Experiments Continued... zMendel studies only seven traits in order to simplify his research: zSeed shape zSeed color zSeed coat color zPod shape zPod color zFlower position zPlant height
Mendel’s Experiments Continued... zMendel crosses plants with different characteristics for the same trait (i.e., both plants have flowers, but the flowers are positioned differently on the plant) zMendel develops hybrids, or organisms with traits from two organisms zMendel sees that the offspring have traits of only one parent and the other has seemingly disappeared. zAll plants are tall with yellow seeds!
Mendel’s Conclusions: zMendel senses that traits are controled by genes and that there must exist two contrasting forms for these genes. zThese different forms of genes are called alleles zOther conclusions follow….
The Principle of Dominance: zSome alleles are dominant while some are recessive zDominant alleles will always express themselves if present zRecessive genes will only be expressed if no dominant allele for the same trait is present
Experiment Results: zTall and yellow alleles are dominant (T & Y) zShort and green alleles are recessive (t & y)
Mendel wants more answers... zAllows all hybrid plants to self-pollinate zAssigns names to generation of plants xP generation: Parental generation (First allowed to self-pollinate) xF 1 generation: First offspring produced by self-pollination (filial generation) xF 2 generation: Offspring of the mixing of F 1 generation
Results of F 1 cross: zThe resulting F 2 plants showed recessive characteristics zHow did the recessive trait “get away” from the dominant allele that masked it?
Law of Segregation: zDuring meiosis, when homologous chromosomes pair-up, one chromosome has one allele whereas the other chromosome has the opposite allele (i.e., one has the tall trait and the other the short)
Question: zDo alleles for one trait have anything to do with other alleles? zIn other words, do alleles control alleles for other traits?
Law of Independent Assortment: zAlleles for one gene DO NOT control alleles for other traits. zIn other words, having blonde hair doesn’t mean that you will definitely have blue eyes.
Summary of Mendel’s Work: zThe factors that control heredity are individual units known as genes. In organisms that reproduce sexually, genes are inherited from each parent. zIn cases in which an organism possesses two forms of the gene for a single trait, some forms of the gene may be dominant and others may be recessive. zThe two forms of each gene are segregated during the formation or reproductive cells. zThe genes for different traits may assort independently of one another.
Basic Genetics Vocabulary zPunnett square: A simple scientific tool used to show the possible combination of alleles in an offspring generation zGametes: offspring that result from the mixing of parental sex cells zPhenotype: The actual physical appearance of the offspring zGenotype: The actual genetic makeup of the offspring zHomozygous: Organisms that have two identical alleles for a trait zHeterozygous: Organisms that have two different alleles for a trait
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