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Intro to Genetics 11.1 The Work of Gregor Mendel Mendel • Austrian Monk • Born in 1822 in the Czech Republic • Studied at University of Vienna – Math and Science • Worked in a monastery and school for 14 years – In charge of garden in the monastery Mendel’s work • Fertilization – Process of male and female reproductive cells joining together. • Used pea plant • Pea are True breeding – If allowed to self pollinate they would produce identical offspring Mendel’s work • Produced Hybrids – Offspring that has parents with different traits – He saw that : ↓ ( fig 11-3 on pg 264) • Seed Shape – Round + Wrinkled Round • Seed Color – Yellow + Green Yellow • Seed Coat Color – Gray + White Gray • Pod Shape – Smooth + Constricted Smooth • Pod Color – Green + Yellow Green • Flower position – Axial + Terminal Axial • Height – Tall + Short Tall Mendel's Conclusion 1. Inheritance is determined by traits passed generation to generation. Now known as Genes each gene has different forms called ALLELES 2. Principle of Dominance: Some Alleles are recessive and some are dominant. • Segregation: alleles are separated • Gametes: Sex cells • Genes are separated into alleles to form gametes Segregation • The splitting of a gene into alleles to form the gamete. – P = parents – F1 = 1st generation – F2 = 2nd generation Meiosis KM 8 TT P segregation F1 Meiosis KM Tt T tt X T Tt t tT t tT 9 Tt F1 segregation F2 Meiosis KM TT T Tt X t Tt T Tt t tt 10 Probability and Punnett Squares Pg 267-269 Genetics and Probability • Probability – The likelihood of a specific outcome happening – Ex: Getting tails when flipping a coin ½ or 50% – If flipping a coin 3 time the probability of it landing on tails all three time • ½ x ½ x ½ = 1/8 or 12.5% Meiosis KM 12 • Genotype – The genes an organism has. • Phenotype – The traits that the organism exhibits. • Homozygous: – When an organism has either both dominate or recessive genes for a given trait • Heterozygous – When an organism has both a dominate and recessive genes for a given trait Meiosis KM 13 Punnett Squares They are used to show possible genotypes and phenotypes (11-7 on pg 268) Meiosis KM 14 • Cross a Rr Tt with an Rr Tt • What % of the genotype is – RR TT & rr tt (all homozygous) – All Heterozygous (Rr Tt) • What is the % phenotype shows – All dominant traits, – All recessive traits Example Aa Bb Dd X Aa Bb Dd • AaBbDd – ABD – ABd – AbD – Abd – aBD – aBd – abd • AaBbDd – ABD – ABd – AbD – Abd – aBD – aBd – abd Mitosis Meiosis KM 17 Meiosis pg 275-281 Meiosis KM 18 Genome • Genome: Complete complement of an organism’s DNA. – Includes genes (control traits) and noncoding DNA organized in chromosomes. Meiosis KM 19 Genes • Eukaryotic DNA is organized in chromosomes. – Genes have specific places on chromosomes. Meiosis KM 20 Heredity • heredity – way of transferring genetic information to offspring • Chromosome theory of heredity: chromosomes carry genes. • Gene – “unit of heredity”. Meiosis KM 21 Chromosome numbers All are even numbers – diploid (2n) sets of homologous chromosomes! Ploidy = number of copies of each chromosome. Diploidy Meiosis KM 22 Meiosis – key differences from mitosis • Meiosis reduces the number of chromosomes by half. • Daughter cells differ from parent, and each other. • Meiosis involves two divisions, Mitosis only one. Meiosis KM 23 Meiosis KM 24 Meiosis 1 First division of meiosis • Prophase 1: Each chromosome duplicates and remains closely associated. These are called sister chromatids. Crossing-over can occur during the latter part of this stage. • Metaphase 1: Homologous chromosomes align at the equatorial plate. • Anaphase 1: Homologous pairs separate with sister chromatids remaining together. • Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair. Meiosis KM 25 Meiosis II Second division of meiosis: Gamete formation • Prophase 2: DNA does not replicate. • Metaphase 2: Chromosomes align at the equatorial plate. • Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole. • Telophase 2: Cell division is complete. Four haploid daughter cells are obtained. Meiosis KM 26 Meiosis KM 27 Meiosis KM 28 Animation Meiosis KM 29 Meiosis creates genetic variation • During normal cell growth, mitosis produces daughter cells identical to parent cell (2n to 2n) • Meiosis results in genetic variation by shuffling of maternal and paternal chromosomes and crossing over. No daughter cells formed during meiosis are genetically identical to either mother or father During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring. Meiosis KM 30 Independent assortment Number of combinations: 2n e.g. 2 chromosomes in haploid 2n = 4; n = 2 2n = 22 = 4 possible combinations Meiosis KM 31 Independent assortment Meiosis KM 32 Crossing over Chiasmata – sites of crossing over, occur in synapsis. Exchange of genetic material between non-sister chromatids. Crossing over produces recombinant chromosomes. Meiosis KM 33 Mitosis vs. meiosis Meiosis KM 34 Meiosis KM 35