Gregor Mendel Austrian Monk Worked with pea plants
A. True Breeding Pea Plants Self pollinate and produce new plants genetically identical to themselves Mendel decides to cross pollinate the plants Offspring are hybrids Mendel studied traits 1. seed shape 2. seed color 3. seed coat color 4. Pod shape 5. Pod Color 6. Flower position 7. Plant height
2 Conclusion 1. Traits are passed from one generation to the next by genes Different forms of genes are called alleles 2. Dominance Principle Some alleles are dominant and some alleles are recessive
B. Segregation Parent plants = P generation Cross fertilize parents, the offspring are called F 1 generation When F 1 plants flower, 2 alleles are segregated so that each gamete (pollen or egg) has one copy of that gene. Tt Egg T Pollen t SUMMARY
Mendel found: Hybrid crossed with a hybrid (Tt) created about ¾ tall and ¼ short I. Genetics and Probability The likelihood that a particular event will occur The Principle of Probability can be used to predict the outcome of genetic crosses
II. Punnett Squares Can be used to predict and compare the genetic variations that will result from a cross Homozygous : TT or tt Heterozygous : Tt Phenotype : physical appearance (tall / short) Genotype : the actual genes (Tt / TT / tt)
I. Independent assortment 2 factor cross Following two different genes as they pass from one generation to the next. A. Two factor cross: F1 Pure breeding plants for 2 traits seed shape and seed color RRYY X rryy B. Two factor cross: F2 The principle of independent assortment state Genes with different traits can segregate independently during the formation of gametes (Dihybrid cross)
II. Summary of Mendel s Principles 1. Characteristics are passed from parents to offspring by genes 2. Some alleles are dominant and some are recessive 3. each adult has 2 copies of a gene that separate when gametes are formed. 4. Alleles for different genes separate independently of each other.
III. Beyond Dominant and Recessive A. Incomplete Dominance One allele is not dominant over the other, so we get a blend of the 2 4 o clock flowers Red x White Pink fowers B. Codominance Both alleles contribute to phenotype White feathers chicken X Black feathers chicken Speckled feathers C. Multiple alleles More than 2 alleles for a trait D. Polygenic traits Having many genes More than one gene involved in producing the phenotype Skin color
Purpose Cell division to produce new cells everywhere in the body except for sex cells. End result: 2 genetically identical daughter cells
4 Stages of Mitosis: PMAT Prophase Metaphase Nuclear envelope breaks down, centrioles and spindles appear, chromosomes become visible. Chromosomes line up in the middle of the cell Anaphase Telophase Chromosomes are separated into chromatids and pulled to opposite ends of the cell Nuclear envelope re-forms, centrioles and spindles disappear, and cytoplasm begins pinching in. Cytokinesis Cell divides into 2 genetically identical daughter cells
I. Chromosome Number Ex: fruit fly 8 chromosomes Homologous chromosomes 4 chromosomes from Dad 4 chromosomes from Mom Diploid Full set of chromosomes Ex: humans 46 fruit fly 8 vs. Haploid Half set of chromosomes Ex: human 23 fruit fly 4
II. Phases of Meiosis Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphse II Anaphase II Homologous chromosomes pair up and form tetrads ******CROSSING OVER OCCURS ********** Chromosomes line up in center of the cell Chromosomes are pulled to opposite ends of the cell Nuclear envelope re-forms and cells divide. 2 new cells Nuclear envelope breaks down, centrioles and spindle form Chromosomes line up in the middle Chromosomes are pulled apart into chromatids. Chromatids are pulled into opposite ends of the cell. Telophase II Cells divide and produce 4 genetically different cells
III. Gamete Formation *Meiosis produces gamete cells Males 4 viable sperms cells Females 1 viable egg cells and 3 polar bodies Summary
I. Gene Linkage Chromosomes assort independently, not individual genes II. Gene Maps The relative location of each known gene on a chromosome 1. If two genes are close together, the recombination frequency between them should be low. 2. If they are far apart, the recombination frequency should be high.
Page 280 Which will you have more of? Purple eyes and speck wings or Brown eyes and speck wings ****Brown eyes and speck wings (closer together)***** Summary