Chapter 14 - CHAPTER 14 - MENDEL AND THE GENE IDEA...

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CHAPTER 14 - MENDEL AND THE GENE IDEA Introduction Every day we observe heritable variations (eyes of brown, green, blue, or gray) among individuals in a population. These traits are transmitted from parents to offspring. One mechanism for this transmission is the “blending” hypothesis. This hypothesis proposes that the genetic material contributed by each parent mixes in a manner analogous to the way blue and yellow paints blend to make green. Over many generations, a freely mating population should give rise to a uniform population of individuals. However, the “blending” hypothesis appears incorrect as everyday observations and the results of breeding experiments contradict its predictions. An alternative model, “particulate” inheritance, proposes that parents pass on discrete heritable units - genes - that retain their separate identities in offspring. Genes can be sorted and passed on, generation after generation, in undiluted form. Modern genetics began in an abbey garden, where a monk names Gregor Mendel documented the particulate mechanism of inheritance. A. Gregor Mendel’s Discoveries 1. Mendel brought an experimental and quantitative approach to genetics Mendel grew up on a small farm in what is today the Czech Republic. In 1843, Mendel entered an Augustinian monastery. He studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and by a botanist who aroused Mendel’s interest in the causes of variation in plants. These influences came together in Mendel’s experiments. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery. The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance. Pea plants have several advantages for genetics. Pea plants are available in many varieties with distinct heritable features ( characters ) with different variants ( traits ). Another advantage of peas is that Mendel had strict control over which plants mated with which. Each pea plant has male (stamens) and female (carpal) sexual organs. In nature, pea plants typically self-fertilize, fertilizing ova with their own sperm. However, Mendel could also move pollen from one plant to another to cross-pollinate plants. In a typical breeding experiment, Mendel would cross-pollinate ( hybridize ) two contrasting, true- breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation .
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Mendel would then allow the F 1 hybrids to self-pollinate to produce an F 2 generation. It was mainly Mendel’s quantitative analysis of F
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Chapter 14 - CHAPTER 14 - MENDEL AND THE GENE IDEA...

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