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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.

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Presentation on theme: "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."— Presentation transcript:

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

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6 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. Locus, the location for a specific gene A pair of alleles Homologuous chromosomes Three pairs of genes or Three pairs of alleles

7 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.

8 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.

9 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

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

11 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

12 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

13 Mendel’s Monohybrid Cross

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15 Probability and Punnet Squares ► A possibility of outcomes and crosses ► Test crosses  Unknown genotype crossed with homozygous recessive

16 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?

17 Fig. 11.9, p. 181 aBaB AB abAbAb AbAb aBaB 1/4 ABab AABB purple- flowered tall parent (homozygous dominant) aabb white- flowered dwarf parent (homozygous recessive) F1 OUTCOME: All F 1 plants purple-flowered, tall (AaBb heterozygotes) X meiosis, gamete formation AaBbAaBbAaBbAaBb Possible outcomes of cross-fertilization AaBbAaBbaabbAabbaaBb AABBAABbAaBBAaBb AABbAAbbAaBbAaBbAabb AaBbAaBbaaBBaaBbAaBB 1/16 ADDING UP THE F 2 COMBINATIONS POSSIBLE: 9/16 or 9 purple-flowered, tall 3/16 or 3 purple-flowered, dwarf 1/16 or 1 white-flowered, dwarf 3/16 or 3 white-flowered, tall

18 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

19 Independent Assortment

20 Theory in Modern Form ► Independent Assortment  Gametes require genes independently of how other pairs of genes were sorted out ► Variety of Offspring

21 Dominance Relation ► Incomplete Dominance  Red snapdragon crossed with white snapdragon > Pink F 1 ► Codominance  Multiple allele system ► ABO Blood types

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