Gregor Mendel

1. Mendel & Heredity Gregor Mendel “Father of genetics”

3. Mendel Successes • 1st to predict how traits are transferred from one generation to next • Successful b/c studied only one trait at a time to control variables & analyzed his data mathematically

4. Mendel’s experiments • Self-pollination true-breeding parent, only 1 plant • Cross-pollination (making a cross)  offspring from two different parent plants

5. More on Mendel’s experiments • Mendel studied 7 traits on pea plants - Seed shape & color, pod color & shape, flower color, flower position, & plant height • Conducted monohybrid crosses looking at only 1 trait • Example – Flower color

7. What’s going on? • The white flower trait had reappeared. • Mendel repeated for other traits and in every case he found that one trait seemed to disappear in the 1st generation only to reappear unchanged in ¼ of the 2nd generation.

8. Mendel’s hypothesis • Organisms have 2 factors that described each trait  alleles • Inherited one allele from father & other from mother

10. Explaining Mendel’s results • A purebred parent plant would have 2 identical alleles for purple flowers (PP) or 2 alleles for white flowers (pp) • F1 offspring have 1 allele for purple flowers & 1 allele for white flowers (Pp) • F2 offspring - pp, Some PP, Pp

11. Mendel’s Law of dominance • Some alleles are dominant (trait is expressed in the offspring) & other alleles arerecessive (trait is only exhibited if dominant is absent) • Ex: Purple & white flowers

12. Law of segregation • Alleles for a trait will separate when the sex cells (gametes) are formed during meiosis. • Evidence – F2 offspring show recessive trait.

13. Law of Independent Assortment • Genes for different traits are inherited independently from each other • Mendel discovered this through his experiments w/dihybrid crosses (2 parents w/2 different traits) • Ex: tall, yellow pea plant with a short, green pea plant

14. Environment affects gene expression • Internal - Age, gender (hormonal differences) • Ex: male bird feathers colorful • External - Temperature, nutrition, light, radiation, chemicals, viruses • Ex: leaves at top of trees

15. Review • Phenotype • What the organism looks like (physical appearance) • Ex: brown hair • Genotype • genetic makeup of an organism (we cannot see this) • Ex: Bb, BB

16. Two forms of Genotype • Homozygous • both identical alleles are either dominant or recessive. • Ex: BB or bb • Heterozygous • different alleles, one dominant & one recessive • Ex: Bb

17. Punnett Squares

18. Punnett Squares (PSq) • Developed in 1905 by Reginald Punnett. • Used to predict & compare possible genetic variations resulting from a cross • Probabilities, not exact results

19. Symbols used in PSq • Original parents  P1 generation • Offspring of the parent plants  F1 generation • Offspring of the F1 generation  F2 generation

20. Example

21. Steps to solving PSq • Identify the dominant & recessive alleles • Write the genotypes of the parents • Determine the possible gametes the parents can produce (how the alleles will separate)

22. Enter the possible gametes at top (#1 parent) & side (#2 parent) of the PSq • Complete the PSq  write the alleles from the gametes in the appropriate boxes • Determine the phenotypes of the offspring and percentages of each

23. PSq Practice • Heterozygous yellow seeds x homozygous green seeds • Key : • Y yellow seeds • y green seeds

24. Answer

26. Now try problems on: • Punnett Square Practice: Monohybrid Crosses worksheet STOP click here

28. Dihybrid cross – like a puzzle • Can 2 parents with Heterozygous round, yellow seeds produce offspring with wrinkled, green seeds? • 1st – determine possible gametes/ allele partners • First • Outside • Inside • Last • Set up PSq boxes

30. Practice Dihybrid Cross • Heterozygous Purple Flower & Homozygous Tall X Homozygous white flower & Heterozygous Tall Key: F purple flower T tall f white flower t short