11 – Introduction to Genetics

1. 11 – Introduction to Genetics

2. The Work of Gregor Mendel • Inheritance other than $$$$ • How did things get passed on? • Genetics – the scientific study of heredity • Mendel, peas and his work • Long overlooked

3. The Role of Fertilization • Male and Female Parts • Fertilization – joining of reproductive cells • Self-pollination • True breeding • Trait • Cross Breeding • Male parts gone • Hybrids

4. Genes and Alleles • P1 and F1 generations • Disappearance of traits • Parent to offspring by genes. • Mendel called them factors • Single gene trait (ex. Tall vs. Short) • Alleles – forms of a gene

5. Dominant and Recessive Alleles • Principle of Dominance • Mendel’s second conclusion • One dominant allele • Organism shows that trait • Recessive Alleles • Only show when dominant is not present

6. SEGREGATION • What happened to the other trait? • Was it still in the F1? • Did an F2 cross • Trait reappeared • Mendel assumed Dominance masks

7. F1 Cross and Gametes • One trait separated from the other • Segregation • During gamete formation • Follow this chart

8. 11.2 – Applying Mendel’s Principles

9. 11.2 Applying Mendel’s Principles – Probability and Punnett Squares • Probability – likelihood that an event would occur. • Mendel analyzed his data • Found probability • Segregation and Outcomes – • Alleles segregate during gamete formation (haploid) • Homozygous vs. Heterozygous

10. Probabilities, Averages, Genotype and Phenotype • Probabilities predict the average outcome • Genetic makeup vs. observable characteristics • Genotype vs. Phenotype • Punnett Squares • Uses math to predict

11. Independent Assortment • Does segregation of one pair affect other pairs? • Two factor (dihybrid) cross • Followed two traits • F1 • F2 • Independent Assortment • Some genes separate independent of each other

12. Summary of Mendel • Characteristics are determined by genes and passed from parents • If there are two or more forms of alleles some may be dominant or recessive • Most adults have two copies of each gene (one from mom and one from dad) and the segregate during gamete formation • Alleles usually segregate independent of each other

13. Summary • Thomas Hunt Morgan • Showed that the same principles apply to animals • Fruit Fly (Drosophila melanogaster)

14. 11.3 – Other Patterns of Inheritance

15. Beyond Dominant and Recessive • Incomplete Dominance • Traits blend • Codominance • Both traits show • Multiple Allele • More than two alleles • Polygenic • Several Genes involved

16. Genes and Environment • Environment can affect gene expression • Phenotype is determined by genotype and environment • Western White Butterfly • Pigment changes • Why?

17. 11.4 Meiosis

18. Chromosome Number • Diploid Cells • Homologous pairs • Diploid (2N) • Inherited from each parent • Segregate during gamete formation • Haploid Cells • Single set of chromosomes

19. Phases of Meiosis • Meiosis • Chromosome # cut by half • Prophase I • Tetrad • Crossing over • Metaphase I and Anaphase I • Paired homologous chromosomes line up

20. Phases of Meiosis • Telophase I and Cytokinesis • Results in 2 daughter cells • Haploid in number • Prophase II • No tetrads • Metaphase II, Anaphase II, Telophase II and Cytokinesis • Similar to Meiosis I but four daughter cells result (gametes) (zygote)

21. Comparing Meiosis and Mitosis • Replication and Separation of Genetic Material • Mitosis • Replicate once, divide once (single chromosomes lined up, full set of chromosomes at end • Meiosis • Replicate once, divide twice (pairs lined up), half the number of chromosomes at end.

22. Gene Linkage and Gene Maps • Gene Linkage (Thomas Hunt Morgan) • Traits assort independently IF • they are on different chromosomes or • Very far apart on same chromosome • If they are fairly close on the same chromosome, they are LINKED • Distance apart on the chromosome is key • The closer the genes are, the more linked they are • Maps are made based on how often crossing over is observed