1. Introduction to Genetics For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids. For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids. It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown. It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown. Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half. Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half.

2. Intro. To Genetics By the 1890's, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction. By the 1890's, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction. The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children. The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children.

3. Gregor Mendel A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right. A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right. His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death

4. Gregor Mendel His early adult life was spent in relative obscurity doing basic genetics research and teaching high school mathematics, physics, and Greek in Brünn (now in the Czech Republic). His early adult life was spent in relative obscurity doing basic genetics research and teaching high school mathematics, physics, and Greek in Brünn (now in the Czech Republic). In his later years, he became the abbot (friar) of his monastery and put aside his scientific work. In his later years, he became the abbot (friar) of his monastery and put aside his scientific work.

5. Gregor Mendel While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms. While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms.

6. Mendel and Peas Through the selective cross- breeding of common pea plants over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics. Through the selective cross- breeding of common pea plants over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics. For instance, the pea flowers are either purple or white-- intermediate colors do not appear in the offspring of cross-pollinated pea plants. For instance, the pea flowers are either purple or white-- intermediate colors do not appear in the offspring of cross-pollinated pea plants.

7. Mendel and Peas Mendel observed seven traits (specific characteristic) that are easily recognized and apparently only occur in one of two forms: Mendel observed seven traits (specific characteristic) that are easily recognized and apparently only occur in one of two forms: flower color is purple or white flower color is purple or white flower position is axial or terminal flower position is axial or terminal stem length is long or short stem length is long or short seed shape is round or wrinkled seed shape is round or wrinkled seed color is yellow or green seed color is yellow or green pod shape is inflated or constricted pod shape is inflated or constricted pod color is yellow or green pod color is yellow or green

9. Mendel’s Peas The pea plant was favorable organism for these studies because it was self-fertilizing The pea plant was favorable organism for these studies because it was self-fertilizing When he made crosses, he followed only 1 or 2 (out of his 7) traits (characters) at a time When he made crosses, he followed only 1 or 2 (out of his 7) traits (characters) at a time He employed a very consistent method: He employed a very consistent method: - Opened flower & placed pollen from one type onto the stigma

10. Mendel’s methods Mendel covered each flower with little bag Mendel covered each flower with little bag When pods were ripe harvested them and planted seeds When pods were ripe harvested them and planted seeds He counted the number of each type of offspring and carefully recorded all of his data. He counted the number of each type of offspring and carefully recorded all of his data.

11. Mendel’s First Experiment Crossed (P1): Pure breeding Tall x Pure breeding Short (Dwarf) Crossed (P1): Pure breeding Tall x Pure breeding Short (Dwarf) (P1) = parental generation (pure breed) (P1) = parental generation (pure breed) Pure (true) breeding means that if the plants were allowed to self- pollinate, they’re offspring would be identical to themselves. Pure (true) breeding means that if the plants were allowed to self- pollinate, they’re offspring would be identical to themselves. Predictions: The offspring would be: Predictions: The offspring would be: All tall All short All intermediate Some would be tall and some short

12. Mendel’s 1st and 2nd Experiment 1st Exp (P1): Crossed 1st Exp (P1): Crossed Pure Tall x Pure Short All offspring (F 1 ): All Tall All offspring (F 1 ): All Tall These offspring of the parental generation are called hybrids, which are offspring with different traits than parents. These offspring of the parental generation are called hybrids, which are offspring with different traits than parents. (F 1 ) = first filia (son or daugther) (F 1 ) = first filia (son or daugther) 2nd Exp: Bred F 1 2nd Exp: Bred F 1 Results: Ratio of 787 tall to 277 short (3:1) Results: Ratio of 787 tall to 277 short (3:1)

13. Mendel’s Principle of Segregation Mendel assumed that the two “Factors” for each trait must exist in the parental germ cells producing the gametes (pollen / egg) Mendel assumed that the two “Factors” for each trait must exist in the parental germ cells producing the gametes (pollen / egg) These “factors” are called alleles. These “factors” are called alleles. Each allele came from the parents and were united in fertilization Each allele came from the parents and were united in fertilization In forming pollen and egg, the two alleles for any trait must separate and go into different gametes In forming pollen and egg, the two alleles for any trait must separate and go into different gametes This became known as Mendel’s “Principle of Segregation” This became known as Mendel’s “Principle of Segregation”

14. Mendel’s Third Experiment Crossed one of the F 1 tall plants with its dwarf parent: Crossed one of the F 1 tall plants with its dwarf parent: F 1 Tall x Dwarf (P 1 ) F 1 Tall x Dwarf (P 1 ) Possible Outcomes: Possible Outcomes: All would be tall Mixture of Tall & Dwarf All would be intermediate Experimental results —> Experimental results —> 50%

15. Mendel’s Notation After the third experiment, Mendel formulated his “Principles of Dominance” which states that some alleles are dominant and some are recessive. After the third experiment, Mendel formulated his “Principles of Dominance” which states that some alleles are dominant and some are recessive. Used capital letter to denote what he called the dominant form of the trait: T = tall Used capital letter to denote what he called the dominant form of the trait: T = tall Used lower case letter to denote what he called the recessive trait: t = short (dwarf) Used lower case letter to denote what he called the recessive trait: t = short (dwarf) Thus for the Tall and Dwarf crosses: Thus for the Tall and Dwarf crosses: TT = Original pure-breeding tall parent tt = Original pure-breeding short parent Tt = Hybrid F 1 offspring Pure-breeding forms later called homozygous Pure-breeding forms later called homozygous Hybrids later called heterozygous Hybrids later called heterozygous

16. Mendel’s Experiment 3 Mendel recognized that it is not always possible to tell what offspring will be like by inspecting the parent Mendel recognized that it is not always possible to tell what offspring will be like by inspecting the parent Mendel could test if tall plants were pure-breeds (homozygotes) or hybrid (heterozygotes) by the “back-cross” or “test- cross” Mendel could test if tall plants were pure-breeds (homozygotes) or hybrid (heterozygotes) by the “back-cross” or “test- cross” Test Cross: Crossing a organism with the dominant phenotype with the same organism with the recessive phenotype to determine the genotype of the dominant organism. Test Cross: Crossing a organism with the dominant phenotype with the same organism with the recessive phenotype to determine the genotype of the dominant organism. Tt tt TT tt Not in your notes

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18. Writing Mendel’s Crosses Using His Notational System It was now possible to account for the 3:1 ratio in the F 1 in Mendel’s second experiment: It was now possible to account for the 3:1 ratio in the F 1 in Mendel’s second experiment: This method of calculating traits of offspring in each generation is called a Punnett square. This method of calculating traits of offspring in each generation is called a Punnett square.

19. Punnett Squares The gene combination that might result from a genetic cross can be determined by drawing a Punnett square. The gene combination that might result from a genetic cross can be determined by drawing a Punnett square. Punnett squares help to determine phenotypes and genotypes. Punnett squares help to determine phenotypes and genotypes. Phenotype – Physical characteristics (Purple) Phenotype – Physical characteristics (Purple) Genotype – Genetic make-up (BB or Bb) Genotype – Genetic make-up (BB or Bb)

20. Independent Assortment After showing alleles segregated during the formation of gametes, Mendel wondered if they did so independently. After showing alleles segregated during the formation of gametes, Mendel wondered if they did so independently. In other words, does the segregation of one pair of alleles affect the segregation of another set of alleles? In other words, does the segregation of one pair of alleles affect the segregation of another set of alleles? Example: Does the gene for seed color have anything to do with the gene for seed shape? Example: Does the gene for seed color have anything to do with the gene for seed shape?

21. Independent Assortment To answer these questions, Mendel performed an experiment to follow two different genes as they passed from one generation to the next. To answer these questions, Mendel performed an experiment to follow two different genes as they passed from one generation to the next. This experiment is known as the Two-Factor Cross or Dihybrid cross. This experiment is known as the Two-Factor Cross or Dihybrid cross.

22. Mendel Extended His Analysis Mendel chose two different characteristics of the pea: Mendel chose two different characteristics of the pea: - Seed Coat: Smooth Wrinkled - Seed color:Yellow Green

23. Two-Factor (dihybrid) Cross First, Mendel crossed pure-breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy). First, Mendel crossed pure-breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy). All of the F 1 offspring produced round yellow peas (RrYy). All of the F 1 offspring produced round yellow peas (RrYy). This proved round and yellow must be dominant alleles. This proved round and yellow must be dominant alleles. Try doing the Punnett square. Try doing the Punnett square.

24. RYRYRYRY ryRrYyRrYyRrYyRrYy ryRrYyRrYyRrYyRrYy ryRrYyRrYyRrYyRrYy ryRrYyRrYyRrYyRrYy RRYY rryyrryy

25. Independent assortment This cross does not indicate whether genes assorted independently. This cross does not indicate whether genes assorted independently. This cross only provided hybrids plants (F 1 ) needed to produce an F 2 generation that would provide the answers to Mendel's question. This cross only provided hybrids plants (F 1 ) needed to produce an F 2 generation that would provide the answers to Mendel's question.

26. Results Mendel knew the F 1 had a genotype of RrYy (heterozygous). Mendel knew the F 1 had a genotype of RrYy (heterozygous). How would the alleles segregate into the F 2 How would the alleles segregate into the F 2 Try the Punnett Square for the cross of F 1 hybrids producing and F 2 generation. Try the Punnett Square for the cross of F 1 hybrids producing and F 2 generation.

27. Results After Mendel counted the offspring of the dihybrid cross, he could make the following conclusion. After Mendel counted the offspring of the dihybrid cross, he could make the following conclusion.

28. Mendel Could Now Make A Second Generalization: Genes for different traits segregate independently during the formation of gametes. Genes for different traits segregate independently during the formation of gametes. This became known as Mendel’s third principle: Independent Assortment This became known as Mendel’s third principle: Independent Assortment

29. A Summary of Mendel’s Principles Mendel’s principles form the basis of the modern science of genetics. These principles can be summarized as follows: Mendel’s principles form the basis of the modern science of genetics. These principles can be summarized as follows: 1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. 2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some form of the gene may be dominant and the other recessive (Principles of Dominance). 3. In most sexually reproductive organisms, each adult has two copies of each gene; one from each parent. These genes are segregated from each other when gametes are formed (Principles of Segregation). 4. The alleles for different genes usually segregate independently of one another (Principles of independent assortment).

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