Mendel and Genetics

1. Mendel and Genetics

2. What is genetics? • Genetics, a branch of biology, is the scientific study of heredity and variation of organisms. • Gregor Mendel, an Austrian monk who studied botany. He made important progress in understanding heredity. • Mendel studied the traits of ordinary garden peas. • During Mendel’s time, the belief was that the traits of the parents blended.

3. Gregor Mendel’s work with plants • Most plants have female and male parts on the same flower. **Male part of the flower produces pollen (sperm). **Female part of the flower produces ova (eggs)

4. Gregor Mendel’s work with plants • Plants reproduce sexually. • Pollen (male gamete) and ovum (female gamete) join making a new diploid cell. • Fertilization produces a new diploid cell. • Two options for the same flower: • Self-pollinating: pollen and ovum come from the same flower. • Cross-pollinating: ovum on one flower and pollen from flower on a different plant..

5. Mendel’s peas • Mendel had pea plants that were true breeding. • Seed from purple flowered plants had only purple flowered offspring. • True breeding plants are ones that produce offspring like themselves. • Mendel experimented with cross pollination between different parents.

6. Gregor Mendel’s work with peas • A trait is a specific observable characteristic that varies from one individual to another. • Seven traits of peas studied by Gregor Mendel: dominant version of trait is on the left, recessive on the right.

7. Crossing different pea plants • P = parental generation • F1 = first filial generation (offspring or children) • F2 = second filial generation (grandchildren) Mendel’s Cross pollination Ptwo different parents, example: trait = height; alleles = tall or short F1 offspring are all heterozygous plants. He used F1 as parents Heterozygotes have different alleles. Homozygotes have the same alleles. F2 ‘grandchildren’ have ratios of 3 out of 4 dominant trait or 75% and 1 out of 4 recessive trait or 25%.

8. Mendel—Father of Genetics • Mendel’s application of scientific method and mathematics to heredity in peas led to his discovery of ‘factors’. • Mendel concluded that biological inheritance is determined by factors passed from one generation to the next. Today, scientists call the factors that determine traits genes.

9. Mendel—Father of Genetics • Each trait that Mendel studied was controlled by one gene that occurred in two contrasting forms. • The different forms of a gene are called alleles • Example—trait is flower color • Gene controls flower color • Two forms are purple and white • Alleles are P-purple, p-white

10. Mendel and his work Mendel predicted: • The role of genes in heredity • Alleles for a gene occur in pairs for an organism • One allele for a gene is in each gamete Mendel had three key concepts: Dominance Segregation Independent Assortment (Day 3)

11. Two of Mendel’s Principles • 1. Law of Dominance: One allele does the ‘talking’. One allele is expressed. One allele was dominant over the other in the F1 generation. • 2. Principle of Segregation: When gametes are formed, the pairs of hereditary factors (alleles) become separated. Each sex cell (egg/sperm) receives only one version of the gene. • 3. Principle of Independent Assortment: Day 3 (Hint: multiple chromosomes divide in meiosis)

12. Gregor Mendel’s ideas • Mendel observed that some traits appeared to dominate. • Dominant allele of gene is always expressed in classic Mendelian genetics. • Other traits skipped a generation. Recessive trait. • A trait is an observable characteristic that varies between individuals. • Mendel counted the results of cross pollination. He calculated the probability of outcomes from his hypothesis. • Probability is how likely something will happen. Mendel assumed the forms of a trait happened as random events with equally likely probabilities. • Consider flipping a coin. Two equally likely outcomes.

13. Using a Punnett Square STEPS: 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square Parents are tall and short.Parent genotypes: TT and t t Cross T T t t

14. Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the p-square 5. determine the possible genotypes of the offspring by filling in the p-square 6. summarize results (genotypes & phenotypes of offspring) T T T T  t t t t Genotypes: 100% T t Phenotypes: 100% Tall plants

15. Monohybrid cross: F2 generation • If you let the F1 generation self-fertilize, the next monohybrid cross would be: T t  T t (tall) (tall) Genotypes: 1 TT= Tall 2 Tt= Tall 1 tt = dwarf Genotypic ratio= 1:2:1 Label your ratio TT:Tt:tt T t T t Phenotype: 3 Tall 1 dwarf Phenotypic ratio= 3:1 Label your ratios tall: short

16. Secret of the Punnett Square • Key to the Punnett Square: • Determine the gametes of each parent… • How? By “splitting” the genotypes of each parent: If this is your cross T T  t t The gametes are: T T t t

17. Once you have the gametes… T T t t  t t T T

18. Another example: Flower color For example, flower color: P = purple (dominant) p = white (recessive) If you cross a homozygous Purple (PP) with a homozygous white (pp):  P P p p ALL PURPLE (Pp) P p

19. Cross the F1 generation:  P p P p • Genotypes: • PP • Pp • 1 pp P p P Phenotypes: 3 Purple 1 White p

20. Stations • Each group will visit all stations. • Station 1—Vocabulary A • Station 2—Punnett Squares • Station 3—Analysis of Punnett Square for Parents • Station 4—Vocabulary B • Station 5—Segregation • Station 6—Phenotype/Genotype • Use your handout to record your work at each station.

21. Resources • Dr. Dennis O’Neill, 2013, Basic Patterns of Genetics, Palomar College http://anthro.palomar.edu/mendel/Default.htm • Paul Anderson, 2013, Mendelian Genetics, Bozeman Science, http://www.youtube.com/watch?v=NWqgZUnJdAY • CrashCourse, 2013, Heredity, Crash Course in Biology, http://www.youtube.com/watch?v=CBezq1fFUEA • Staff, 2013, Glossary of Terms, Palomar College, http://anthro.palomar.edu/mendel/glossary.htm