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Chapter_14_Mendel_and_the_Gene_Idea - Mendel and the Gene...

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Basic Terms Gene - heritable units parents pass on to offspring Character - a heritable feature Trait - each variant for a character. ex. purple or white Allele - the alternative versions of a gene Phenotype - the appearance of an organism Genotype - the genetic make up of an organism Homozygous - an organism having a pair of identical alleles for a character Heterozygous - an organism having two different alleles for a character Recessive - the recessive allele is only expressed if both alleles are recessive Dominant - if two different alleles are present the dominant is the one that is expressed Mendel and the Gene Idea Monohybrid Cross Law of Segregation Dihybrid Cross Law of Independent Assortment Testcross Genetics and Probability Gregory Mendel bred pea plants in order to study inheritance. He usually bred two different true-breeding (when self- pollinated the offspring are of the same variety) plants. The crossing of two varieties like this is called hybridization . In a monohybrid cross (a cross that tracks one character) the P Generation (true breeding parents) are mated to produce the F 1 Generation (the hybrid offspring). The hybrids reproduce to create the F 2 Generation (grandchildren). The F stands for filial , meaning offspring. Mendel’s analysis of flower color revealed that the blending model of inheritance was not correct for peas. The characters Mendel observed were either-or (ex. the flowers were either purple or white). Furthermore, there were no white flowers in the F 1 generation , but there were white flowers in the F 2 generation . Thus, Mendel determined that the heritable factor for white flowers was being masked by the purple flower factor in the F 1 generation . He called the purple flower trait dominant and the white flower trait recessive . After analyzing the F 2 Generation of his pea plants, Mendel came up with a fundamental principle of genetics, the law of segregation (The two alleles for each character segregate during gamete production).
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