Lec11notescomplete - Bio1A Lecture 11 Complete Chapter 14...

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Bio1A Lecture 11 Complete 1 Chapter 14: Mendel and the Gene Idea Drawing from the Deck of Genes E What genetic principles account for the passing of traits from parents to offspring? E The “ blending hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) E The “ particulate hypothesis is the idea that parents pass on discrete heritable units (genes) E Mendel documented a particulate mechanism and discovered the basic principles of heredity by breeding garden peas in carefully planned experiments Mendel’s Experimental, Quantitative Approach E Advantages of pea plants for genetic study: E There are many varieties with distinct heritable features, or characters (such as color); character variations are called traits E Mating of plants can be controlled E Each pea plant has sperm-producing organs ( stamens ) and egg-producing organs ( carpels ) E Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another Fig.14-2 Mendel’s Plants E Mendel chose to track only those characters that varied in an “either-or” manner E He also used varieties that were “true-breeding” (plants that produce offspring of the same variety when they self-pollinate) Mendel’s Experiments E In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization E The true-breeding parents are the P generation E The hybrid offspring of the P generation are called the F1 generation E When F1 individuals self-pollinate, the F2 generation is produced The Law of Segregation E When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple E When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white E Mendel discovered a ratio of about three to one , purple to white flowers, in the F2 generation Fig. 14-3 Dominant and Recessive Traits E Only the “purple flower factor” seemed to affect flower color in the F1 hybrids, so Mendel called the purple flower color a dominant trait and white flower color a recessive trait
Bio1A Lecture 11 Complete 2 E Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits E What Mendel called a “heritable factor” is what we now call a gene Mendel’s Model E Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring E Four related concepts make up this model E These concepts can be related to what we now know about genes and chromosomes Concept 1 E The first concept is that alternative versions of genes account for variations in inherited characters E For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers E These alternative versions of a gene are now called alleles E Each gene resides at a specific locus on a specific chromosome Fig. 14-4

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