Mendelian Genetics

1. Mendelian Genetics Study of heredity developed by Gregor Mendel

2. Mendel’s Three Laws Law of Dominance Law of Independent Assortment Law of Segregation

3. Genetics- study of heredity Trait- a characteristic that can be passed from parent to offspring. Gregor Mendel – “the father of modern genetics” used pea plants to study how traits were passed on among generations. Applied mathematics to make statistics on how traits are passed along.

4. Why Pea Plants? • Mendel chose pea plants for 3 reasons: • The structure of the pea flower • The presence of distinctive traits • Rapid reproduction cycle He was able to isolate and control variable. - Cut anthers and only pollinated with desired pollen

5. Purebred- an organism that possesses identical alleles for a particular trait. -homozygous (same alleles) - receives the same genetic traits from both parents Hybrid- an organism that possesses different alleles for a particular trait. -heterozygous (different alleles)

6. Study Mendel’s experiment from page 132 P = parental F1 = filial (offspring) first generation F2 = second generation Which trait is dominant? Chartreuse is dominant.

7. Genes- section of a chromosome that code for a specific trait. • Mendel called them “elements” • allele- a distinct form of a gene (ex: brown hair) • Dominant allele- form of a gene that is always fully expressed when two genes are present. • Recessive allele- form of a gene that is not expressed when paired with a dominant allele.

8. Genotype- the genetic makeup of an organism • Bb • TT • Ll • Phenotype- the outward expression of a trait ( an organism’s appearance) • Brown • Tall • Long haired

9. 6.3 Probability- Predicting the likelihood of an event or outcome. Using fractions, percentages, or ratios. 1/2 50% 1:1

10. Probability in Biology Used to predict the phenotypes and genotypes of offspring in breeding experiments. Can even predict the numbers of kinds offspring before fertilization takes place. Scientists use a tool to make these predictions. Punnett square

11. Punnett square- a grid for organizing genetic information. • Shows probabilities, not actual results. • The study of the inheritance of only one trait at a time. - monohybrid cross • Cross a yellow pea plant with a green pea plant. (Purebred Cross) • Use a Punnett square, show genotypic ratios and phenotypic ratios.

12. Yellow x green YY x yy Genotype Phenotype

13. Cross a heterozygous yellow pea plant with a heterozygous yellow pea plant. • Monohybrid cross • Use a Punnett square, show genotypic ratios and phenotypic ratios. • Turn in your book to page 138 Figure 6.8.

14. Hybrid Cross F1 Yellow vs F1 Yellow Yyx Yy Genotype Phenotype

15. Two Traits Apply the same rules of probability. The inheritance of two traits at the same time - dihybrid cross Cross two heterozygous round, heterozygous yellow pea plants. Punnett square 4 x 4. Use a Punnett square, show genotypic ratios and phenotypic ratios.

16. Dihybrid Cross RrYy x RrYy Genotype Phenotype

17. Test Cross If dominant, how do you know whether it is homozygous or heterozygous? By doing a test cross. Test cross- crossing the organism with an unknown genotype with a homozygous recessive organism. If the unknown genotype is heterozygous, Yy, about 50%the offspring should show the recessive phenotype. If the unknown genotype is homozygous, YY, 100% the offspring will show the dominant phenotype. Figure 6.10 shows this.

18. Test Cross- Practice Problems How do you know if the plant is a heterozygous or homozygous tall wheat plant? Tall wheat plant x short wheat plant F1 Genotypes Phenotypes

19. Test Cross Examples Ability to roll tongue x inability to roll tongue What is the genotype of the parent with the ability to roll their tongue, if they have 2 children that can roll their tongue and 2 children that cannot?