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Introduction to Genetics
Chapter 11 Lecture Notes
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11 – 1 The Work of Gregor Mendel
Austrian monk “Father of Genetics" Reported and published results in mid 1860’s Did not get recognition for his work Importance of his work was rediscovered in 1900
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Experimented with pea plants to see how they passed on traits
Purple/white flower Axial/Terminal flower Yellow/green peas Round/wrinkled peas Green/Yellow pod Inflated/Constricted pod Tall/short
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Crossed short stemmed with other short stemmed = short stemmed plants
Genetics - the study of how traits are passed from parents to offspring Chose Pea plants Had a lot of different traits Reproduce rapidly Cross plants with different traits Crossed short stemmed with other short stemmed = short stemmed plants True breeding short plants Crossed tall stemmed with other tall stemmed plants = some tall, some short Some tall stemmed plants that only produced other tall stemmed plants True breeding tall plants
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True breeding short x True breeding tall plant = all tall plants
F1 generation Two factors for any one trait Dominant and Recessive genes Dominant trait - trait that is stronger Recessive trait - weaker trait, masked by dominant Hybrid - plant has one dominant and one recessive trait
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Each parent had a gene pair
TT (true breeding tall plant) tt (true breeding short plant) Tt (hybrid) Cross hybrid plants from F1 = some tall, some short in a ratio of 3:1, called the F2 generation
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11 – 2 Probability & Punnett Squares
Determines chance offspring have of inheriting certain traits. Chance that an action will occur randomly Results of chance events don’t effect results of the next Each event happens independently Punnett Squares Crossing organisms showing one genetic trait
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Homozygous Heterozygous Phenotype Genotype TT or tt
Has 2 identical alleles True breeders Heterozygous Tt Alleles are different Hybrid Phenotype Physical appearance Tall or short Genotype Genetic makeup TT, Tt, or tt
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11 – 3 Exploring Mendelian Genetics
Independent Assortment Genes that segregate independently Two-factor cross Two genetic traits R = round seeds r = wrinkled seeds Y = yellow seeds y = green seeds Cross homozygous parents Parents RRYY x rryy Offspring all RrYy heterozygous
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Mendel’s Principles Inheritance of genes passed to offspring
Cross heterozygous parents RrYy x RrYy F2 Generation offspring Round Yellow 9/16, Round Green 3/16, Wrinkled Yellow 3/16, Wrinkled Green 1/16 Mendel’s Principles Inheritance of genes passed to offspring For 2 or more alleles genes can have dominant or recessive traits Sexual reproducers have 2 copies of each gene Genes are segregated independently in gamete production
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Beyond Dominant and Recessive Alleles
Incomplete Dominance Heterozygous phenotype is in between homozygous phenotypes Four O’clock pink flowers Codominance Both alleles contribute to phenotype Type AB blood Multiple Alleles One gene with more than two alleles Coat color in rabbits
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Genetics and the environment
Polygenic traits Traits controlled by two or more genes Eye color, skin color, hair color Genetics and the environment Characteristic traits are coded for in genes Environment can determine traits Nutrition Disease
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11 – 4 Meiosis Walther Flemming (1882) Chromosomes German biologist
Discovered chromosomes Chromosomes Protein composed of “Nucleic Acid" Located in the nucleus of a cell Provide the code to make proteins Build Repair Reproduce
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Meiosis Division of sex cells Produces egg or sperm cells Each cell produced has 1/2 the regular genetic information (haploid (N))
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2 haploid daughter cells are formed Meiosis II
Interphase I Chromosome replication Each parent provides one chromosome Each chromosome is replicated 4 copies of 1 type of chromosome Meiosis I Prophase I Chromosome homologs pair up (tetrad) Chromatids portions exchange (crossing over) Metaphase I Spindle fibers attach to chromosomes Anaphase I Homologs are pulled away from each other Telophase I and Cytokinesis 2 haploid daughter cells are formed Meiosis II Prophase II (2 haploid daughter cells) Metaphase II Anaphase II Sister chromatids are pulled apart Telophase II and cytokinesis 4 haploid daughter cells are formed
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Gamete Formation (in animals)
4 male gametes are formed (sperm) 4 female gametes formed (1 egg, 3 polar bodies) Comparing mitosis and meiosis Mitosis 1 cell division 2 Diploid (2N) daughter cells Asexual reproduction Meiosis 2 cell divisions 4 haploid (N) daughter cells Gamete formation for sexual reproduction
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11 – 5 Linkage and Gene Maps Gene Linkage Gene Maps
Genes on the same chromosome Genes do not show independent assortment Gene Maps Crossing over changes gene location on homologous chromosomes Show locations of genes on chromosomes
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