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:
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. ► 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.
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
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
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
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.
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.
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
Terms cont. ► P = Parental generation ► F1 = The first generation ► F2 = The off-spring from the mating of the first generation together
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
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
Mendel’s Monohybrid Cross
Probability and Punnet Squares ► A possibility of outcomes and crosses ► Test crosses Unknown genotype crossed with homozygous recessive
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?
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
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
Theory in Modern Form ► Independent Assortment Gametes require genes independently of how other pairs of genes were sorted out ► Variety of Offspring
Dominance Relation ► Incomplete Dominance Red snapdragon crossed with white snapdragon > Pink F 1 ► Codominance Multiple allele system ► ABO Blood types