Mendelian Genetics Gregor Mendel (1822-1884) was an Austrian monk who discovered the basic rules of inheritance. From 1858 to 1866, he bred garden peas in his monastery garden and analyzed the offspring of these mating’s. Law of Dominance When Mendel crossed two true-breeding pea plants that showed contrasting traits, only one of the traits were evident in the offspring. For example, if he crossed a purple flowered pea plant with a white flowered plant, all the offspring were purple. This purple trait was described as dominant. The white trait was described as recessive. The law of dominance states that when dominant and recessive alleles exist together the dominant trait is expressed while the recessive is masked and not expressed. The pure-breeding parent generation is call the P generation. The offspring of the crosses between members of the P generation are called the first filial or F1 generation. Crosses between the F1 generations produce the F2 generation and so on. Dominant alleles (genes) of a trait are usually symbolized by a capital italicized letter (P = purple) and recessive alleles of the same trait are symbolized by a lower case italic letter (p = white). In a previous lesson we learned that fertilization brings together two homologous chromosomes that were separated during meiosis. The resulting zygote will usually have two alleles (genes) for a given trait. When the two inherited alleles are alike (PP or pp) they are described as homozygous. When the two members of an allelic pair are different (Pp) they are termed hybrid or heterozygous. The physical appearance of the offspring is referred to as the phenotype and the gene combinations are referred to as the genotype. Use the following cross to answer the questions that follow. {PP x pp} a. Why is this cross referred to as the P generation? b. The genotype of the plants with purple flowers may be _______________ c. The genotype of the white flowers is _______________________ d. The offspring of the cross make up the _______________ generation. e. The phenotype and genotype of the F1 generation is ___________________________ and _____________ f. The offspring in this cross are also referred to as ____________________________. g. If all the monohybrid offspring have purple flowers, how does illustrate the law of dominance?________________________________________________________________________________________________ ______________________________________________________________________________________________________________
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1866, he bred garden peas in his monastery garden and ...
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