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Genetics Genetics What is Genetics ? Genetics is the study of heredity and variation Examples of genetic variation 1. Domesticated species 2. Human genetics 3. Natural Populations History of Genetics •Domestication of animals •Cultivation of plants Cultivated varieties Animal Breeds Human Genetic Variation Variance Which suspect matches the blood stain ? Bloodstain Ethical Issues Boot GM out of animal feed Cloning Genetic Journals • American Journal of Medical Genetics Clinical Genetics • Developmental Genetics Human Molecular Genetics • Hereditas Opthalmic Genetics • Japanese Journal of Human Genetics Human Genetics • Journal of Heredity Current Genetics • Genetics European J. of Human Genetics • Molecular Biology and Evolution Animal Genetics • Genetics Selection Evolution Nature Genetics • Molecular Ecology Brazilian J. Genetics • Genetika Fungal Genetics and Biology • Molecular and General Genetics Biochemical Genetics • Genome Cancer Genetics and Cytogenetics • Theoretical and Applied Genetics J. of Medical Genetics • Genomics American J. Human Genetics • Trends in Genetics Basic Concepts of Genetics Nucleus - contains genetic material DNA - genetic material 4 bases (nucleotides G, C, A, T) Gene - functional unit of heredity sequence of 4 nucleotides Chromosome -linear DNA molecule Basic Concepts of Genetics Cell/nuclear division • Mitosis (somatic tissue): identical cells • Meiosis (germ tissue): gametes Basic Concepts of Genetics • Mendelian Genetics (transmission genetics) • Molecular Genetics (hereditary material) Historical Notes 1865 Gregor Mendel - controlled genetic experiments (garden peas) - statistical regularity - theory of inheritance Understanding Genetics • Relationship between: GENOTYPE ENVIRONMENT PHENOTYPE set of genes morphology inherited physiology behaviour Mendelian Genetics Requirements: 1. Attributes of the phenotype that vary among individuals 2. Phenotypic variation caused by genetic differences Genotype and Phenotype • The genotype is our actual genes. We cannot see our genes. • The phenotype is the physical expression of those genes. Mendelian Genetics • Genes - cannot be observed directly • Phenotypes - observed directly ** inheritance of phenotypes used to infer the inheritance of genes Mendel’s Experiments Seven Pea varieties “True Breeding Lines” Character “traits” Phenotypes 1. seed shape round, wrinkled 2. seed colour yellow, green 3. flowers (pods) axial, terminal 4. pods full, constricted 5. pods yellow, green 6. flowers violet, white 7. stem tall, dwarf Fertilization Gametes carry the genetic information about an organism. The male gamete produce Sperm. The female gametes produce Eggs. The process in which one gamete is united with another is called Fertilization. Fertilization Mommy Daddy BABY Self-Fertilization • When an organism has both male and female gametes, they are able to selffertilize. Advantages • easy to grow • matures in a season • self-fertilizing • easy to cross-fertilize Dominance • Some characteristics overshadow others when crossed. • This is referred to as a Dominant trait. • The unseen trait is said to be Recessive. • Dominant traits are represented on charts by a capital letter. • Recessive traits are represented by a lower case letter Pure Lines (Homozygous) • When an organism is said to be of pure lines, it means their genotype is two identical alleles. • TT is the pure line for a tall plant. • tt is the pure line for a short plant. Hybrids (Heterozygous) • When parents of two different pure lines are crossed, the offspring are called hybrids. • A hybrid’s genotype consists of two different alleles. • The genotype Tt would be a tall plant hybrid. Homozygous and Heterozygous • When an organism has identical alleles, it is said to be homozygous. • TT, and tt would both be homozygous • When an organism has two different alleles, it is heterozygous. • Tt is heterozygous. Punnett Square T T T T TT TT TT TT Cross Pollination Punnett Square of Cross Pollination MOM DAD T T T t TT Tt TT Tt Punnett Square (Monohybrid Cross) MOM DAD T t T t TT Tt Tt tt Punnett Square MOM DAD t t T t Tt tt Tt tt Punnett Square MOM DAD t t t t tt tt tt tt Mendel’s Experimental Approach Suitable experimental organism • examine few traits in each experiment • accurate quantitative records • analyzed data formulated hypotheses Genetic Analysis (pea shape) Hypothesis to explain results 1. Hereditary determinants (genes) 2. Each adult plant has a gene pair F1 plants: one gene dominant phenotype one gene recessive phenotype Hypothesis (continued) 3. Members of a gene pair segregate equally into the gametes 4. Each gamete has only one member of a gene pair 5. Gametes combine at random to form zygote Hypothesis Self Fertilization Test of Equal Segregation Hypothesis Principle of Segregation Three parts: 1. Hereditary characteristics are determined by distinct units or factors. 2. For each characteristic, an individual carries two factors, one inherited from each parent. 3. The two factors of each pair segregate from each other and end up in separate gametes. If a plant is short, what is its genotype? • It must be homozygous recessive, tt. If a plant is tall, what is its genotype? • It could be homozygous dominant, or heterozygous. TT, or Tt. • To determine which genotype it is we use a test cross. Test Cross Heterozygous Known homozygous recessive t t T t Tt tt Tt tt 1/2 Tall 1/2 Short Test Cross Homozygous Known homozygous recessive t t T T Tt Tt Tt Tt All Tall N0 Short Genetic Terminology Genes: hereditary elements • Alleles: forms of a gene: A a • Heterozygote: Aa • Homozygotes: AA aa • Genotype: Genetic makeup • Phenotype: What we actually see • Dominance AA, Aa same phenotype Summary Experimental: 1. Two pure breeding lines 2. Cross --------> F1 hybrid 3. Self F1 ------> F2 Summary Results: 1. F1 one phenotype 2. F2 3:1 ratio of 2 phenotypes Summary Inference: 1. Single major gene 2. dominant phenotype 3. equal segregation 4. existence of genes inferred