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Genetics

Genetics. Gregor Mendel. Gregor Johann Mendel. Gregor Mendel In 1865 turned the study of heredity into a science His work was so brilliant and unprecedented at the time it appeared that it took thirty-four years for the rest of the scientific community to catch up to it.

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Genetics

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  1. Genetics Gregor Mendel

  2. Gregor Johann Mendel • Gregor Mendel In 1865 turned the study of heredity into a science • His work was so brilliant and unprecedented at the time it appeared that it took thirty-four years for the rest of the scientific community to catch up to it. • His short monograph, "Experiments with Plant Hybrids," in which Mendel described how traits were inherited, has become one of the most enduring and influential publications in the history of science.

  3. Theory of Genetic Blending • Before Mendel’s work, plant and animal breeders based their work on the theory of “Blending”. • This theory states that parents with different traits produced offspring of intermediate appearance. • Example: Red X White flowers = Pink flowers • When red or white flowers reappeared in future generations it was due to the instability in the genetic material

  4. Mendel’s Experimental Approach • Mendel experimented with pea plants • This was a great model to do genetics on • Self fertilizing • Cross fertilize • Breed true • Clear and contrasting traits

  5. Genetic terms • Genes: segments of DNA that provide the information for traits and characteristics • Locus: The location of a specific gene on a specific Chromosome • Allele: alternative forms of a gene. Homologuous chromosomes Locus, the location for a specific gene A pair of alleles Three pairs of genes or Three pairs of alleles

  6. Terms cont. • Diploid is a 2n organism with two complete sets of genetic information. • Haploid is a 1n organism or cell with a single complete set of genetic information • Homozygous is when both alleles for a trait are the same • Heterozygous is when the alleles for a particular trait are different.

  7. Terms cont. • Dominant alleles: An allele that is expressed and hides or masks “Recessive” alleles. • Symbolizes as a capital letter. • Example “AA” in homozygous dominant. • Recessive allele: An allele that is expressed in the homozygous form only. • Symbolized as a lower case letter • Example: “aa” in homozygous recessive.

  8. Terms cont. • Genotypes: The actual alleles that are present in an individual. • Example: • Homozygous dominant = AA • Heterozygous = Aa • Homozygous recessive = aa • Phenotype: is the observable characteristic. It is the combination of genes and environment

  9. Terms cont. • P = Parental generation • F1 = The first generation • F2 = The off-spring from the mating of the first generation together

  10. Mendel’s Monohybrid experiments • Realizing that the blending theory didn’t fit with what he was observing Mendel developed an alternative hypothesis • Hypothesis: He said “Genes are particulate factors that passes unchanged from parent to progeny unchanged”. • Some traits mask or hide other traits

  11. Mendel’s Theory of Segregation • Monohybrid cross • Crossing parents to observe a single trait in the off-spring • Gene segregation • Each parent randomly contributes one set of genetic information to the offspring

  12. Mendel’s Monohybrid Cross

  13. Mendel’s Monohybrid Cross

  14. Probability and Punnet Squares • A possibility of outcomes and crosses • Test crosses • Unknown genotype crossed with homozygous recessive

  15. Independent Assortment • Do genes assort randomly in the gamets? • Do some genes prefer the company of other genes? • Example: If one is good at music are also likely to be good a math as well?

  16. X AABB purple- flowered tall parent (homozygous dominant) aabb white- flowered dwarf parent (homozygous recessive) ADDING UP THE F2 COMBINATIONS POSSIBLE: ab ab ab 9/16 or 9 purple-flowered, tall 3/16 or 3 purple-flowered, dwarf aB AB AB aB Ab AB Ab 3/16 or 3 white-flowered, tall 1/16 or 1 white-flowered, dwarf F1 OUTCOME: All F1 plants purple-flowered, tall (AaBb heterozygotes) AaBb AaBb meiosis, gamete formation 1/4 1/4 1/4 1/4 1/4 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb 1/4 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/4 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb 1/4 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb Fig. 11.9, p. 181 Possible outcomes of cross-fertilization

  17. Mendel’s Theory of Segregation • Diploid cells have pairs of genes or homologous chromosomes • During meiosis the two genes segregate and wind up in different gametes

  18. Independent Assortment

  19. Theory in Modern Form • Independent Assortment • Gametes require genes independently of how other pairs of genes were sorted out • Variety of Offspring

  20. Dominance Relation • Incomplete Dominance • Red snapdragon crossed with white snapdragon ---------> Pink F1 • Codominance • Multiple allele system • ABO Blood types

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