Chapter 9 Notes (1).docx - Chapter 9 Patterns of...

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Chapter 9: Patterns of Inheritance Mendel’s Laws The study of genetics has ancient roots Hippocrates’ inheritance explanation was wrong: said that “pangenes” from each part of an organism’s body went to gametes and then passed to next generation, pangenes also passed on bodily changes Instead, reproductive cells are not made from somatic cell particles, and somatic cell changes do not influence eggs and sperm Biologists found that offspring inherit traits from both parents through plants “Blending” hypothesis: inherited traits from mom and dad blended like color blending in offspring, and that colors cannot be unblended Rejected because traits reappear in later generations The science of genetics began in an abbey garden Heredity : transmission of traits from one generation to the next Genetics: the scientific study of heredity Gregor Mendel created the fundamental principles of genetics by breeding garden peas: said that parents pass discrete “heritable factors”, genes which retain their individuality through generations and can be sorted, to offspring Used peas because they have short generation times, produce many offsprings at once which have distinguishable traits, able to control mating Character: a heritable feature that varies among individuals (flower color) Trait: a variant for a character (purple or white) Pea plant mating could be controlled since the petals of pea flower completely enclosed reproductive organs: stamens and carpel Able to self-fertilize: sperm carrying pollen grains from stamen land on egg containing carpel of same flower Mendel did self-fertilization by covering flower with a small bag to contain pollen Did cross-fertilization (fertilization of plant by different plant’s pollen) by 1) prevented self-fertilization by cutting off immature stamens pre-pollen 2) dusted its carpel with another plant’s pollen 3) carpel made pod which contained seeds (peas) that he planted Identified true-breeding varieties and then asked what would happen if crossed Hybrids: 2 different varieties’ offspring (genetic) cross: its cross-fertilization/hybridization P generation: true breeding parents, F1 generation: hybrid offspring F2 generation: F1 fertilized offspring Mendel’s law of segregation describes the inheritance of a single character Monohybrid: cross following 1 character (flower color) True breeding (purple) and true breeding (white) cross → F1 = purple, F2 = 3(purple) : 1(white) because purple factor masked white factor (still there) and F1 plants carried 2 factors (purple and white) Mendel’s 4 hypotheses There are alternative versions of genes that account for variations in inherited characters (flower color gene has 2 versions: purple one, white one); alleles: alternative versions of a gene For each character, an organism inherits 2 alleles, one from each parent; alleles can be same or different: homozygous: gene has 2 identical alleles (homozygote for trait), heterozygous: gene has 2 different alleles

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