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Chapter 2Plant life cycle and phenotypic plasticityNicholas [email protected] Life cycle of an angiospermMitosisMoss Life Cycle• 2n (Diploid)generationvery short• 2n (Diploid)dependant onn (haploid)Fern Life cycle• 2n (Diploid)generationlong, n(haploid) short• n (haploid)independentfrom 2n(diploid)2.14 Life cycle of an angiosperm• 2n (Diploid)generationlong, n(haploid) veryshort• n (haploid)dependent on2n (diploid)Embryo3n2nAn explanation of the previous slide from an article in The New York Times:When a pollen grain fertilizes an egg, it provides two sets of DNA. While one set fertilizes the egg, the other is destined for thesac that surrounds the egg. The sac fills with endosperm, a starchy material that fuels the growth of an egg into a seed. It alsofuels our own growth when we eat corn, rice or other grains.In the first flowers, the endosperm ended up with one set of genes from the male parent and another set from the female parent.But after early lineages like Amborella and water lilies branched off, flowers bulked up their endosperm with two sets of genesfrom the mother and one from the father.Dr. Friedman, of the University of Colorado, Boulder, has documented the transition and does not think it was a coincidence thatflowering plants underwent an evolutionary explosion after gaining an extra set of genes in their endosperm. It is possible, forexample, that with extra genes, the endosperm could make more proteins.“It’s like having a bigger engine,” Dr. Friedman said.Other experts agree that the transition took place, but they are not sure it is the secret to flowers’ success. “I don’t know why itshould be so great,” Dr. Doyle said.As Dr. Friedman has studied how the extra set of genes evolved in flowers, he has once again been drawn to Goethe’s vision ofsimple sources and complex results.Flowers with a single set of female DNA in their endosperm, like water lilies, start out with a single nucleus at one end of theembryo sac. It divides, and one nucleus moves to the middle of the sac to become part of the endosperm.Later, a variation evolved. In a rose or a poppy, a single nucleus starts out at one end of the sac. But when the nucleus divides,one nucleus makes its way to the other end of the sac. The two nuclei each divide, and then one of the nuclei from each end ofthe sac moves to the middle.Duplication, a simple process, led to greater complexity and a major change in flowers.“Nature just doesn’t invent things out of whole cloth,” Dr. Friedman said. “It creates novelty in very simple ways. They’re notradical or mysterious. Goethe already had this figured out.”Where Did All the Flowers Come From?By CARL ZIMMERPublished: September 7, 2009http://www.nytimes.com/2009/09/08/science/08flower.html?ref=scienceReactions to Environmental StressAnimals - movementPlants - amazingdevelopmental changesStress Adaptation #1Stress out a mango tree byhammering nails in it, or pouringsalt on it and you get more fruit.2.15 Phenotypic plasticity in plantsStress Adaptation #2Low Light High


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