ngrid I Shih BIO 1305-08 25 October 2010
I n he r i tance, Genes, and C h romosomes
12.1- What Are the Mendelian Laws of Inheritance? Early ideas of heredity Each parent contributes equally to offspring o Reciprocal crosses- which plants were crossed in both directions Hereditary determinants blend in offspring. Mendel brought new methods to experiments on inheritance Austrian monk Father of Modern Genetics Studied under Doppler at the University of Vienna Over a 7-year period, Mendel spent working out some principles of inheritance in p lants, Mendel made crosses with hundreds of plants and noted the resulting characteristics of 24,034 progeny. Work is a definitive example of extensive preparation, meticulous execution and i maginative but logical interpretation. Mendel devised a careful research plan Studies the common garden pea o Ease of cultivation o Feasibility of controlled pollination o Varieties with contrasting t raits Character - is an observable physical feature T r ait - particular form of a character He r itable t rait - one that is passed from parent to offspring T r ue-breeding - the observed t rait was the only form present for many generations Mendel performed his crosses: o Removed anthers from one parent so it couldnt self-pollinate, pollen collected f rom the other parent and place i t on the stigmas of the first f lower. The plants p roviding and receiving the pollen are known as the p arental generation (P ). o The seed and the resulting new plants constituted the f i rst filial generation (F 1). Mendel and his assistants examined each F 1 p lant to see which t raits it bore o and then recorded the number of F 1 p lants expressing each t rait. In some experiments the F 1 p lants were allowed to self-pollinate and produce a second filial generation (F 2). Each F 2 p lant was characterized and counted.
I ngrid Shih BIO 1305-08 25 October 2010 Mendels fi rst experiments involved monohybrid crosses Hyb r id - refers to the offspring of crosses between organisms differing in one or more t raits. Monohybrid cross Reciprocal cross- in which the parental source of each t rait is reversed: he placed pollen from the spherical-seeded strain on the stigmas of f lowers of the strain with w r inkled seed. Dominant Recessive -
Mendel concluded that one t rait would be dominant over the other t rait. Support for the Particulate Theory Particulate theory- the units of inheritance rating their integrity in the presence of other units Diploid- 2 copies of each set of heritable unit in an organism