11 – Introduction to Genetics

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

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

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

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

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

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

11.2 – Applying Mendel’s Principles

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

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

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

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

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

11.3 – Other Patterns of Inheritance

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

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

11.4 Meiosis

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

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

Phases of Meiosis Telophase I and Cytokinesis Prophase II 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)

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.

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