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PSY354H5 (39)
Chapter 2

Chapter 2 - Sex and Evolution

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Brett Beston

NotesFromReadingCHAPTER2SEXANDEVOLUTIONPGS2958DIVERSE METHODS OF REPRODUCTION HAVE EVOLVEDEvolution The change in the genetic makeup of living populations over time Charles Darwin laid out the principles of evolution in The Origin of Species 1859 suggesting that individuals within a single species differ slightly from one another ie length of nosesThese differences are Heritable Capable of being passed down from parent to offspringNatural Selection The survival and reproduction of those individuals that are best adapted to their environment Gene A stretch of DNA that is transcribed as a functional unit a unit of inheritanceDNA Deoxyribonucleic Acid The linear molecule that forms the chemical basis of genes in all species expect some virusesChromosome A rodshaped nuclear organelle composed of DNA and associated proteinGenome An organisms entire complement of DNA including all its genes In some viruses such as HIV the genome is composed of RNAConjugation Contact between two bacteria accompanied by the transfer of a short stretch of DNA from one to the otherTwo bacteria connected by a fine hairlike tube called a pilus and a short piece of DNA called a plasmid passes through the pilus from the donor to the recipient bacterium The plasmid may later become integrated into the recipient bacteriums main genomeEukaryote An organism whose cells contain nuclei Eukaryotic animals greatly diversified in the socalled Cambrian explosion 545 mya when all the main kinds of body plans that now existanthropod vertebrate sponge and so onfirst appeared Mitosis Cell division in which the chromosome number is preserved The result is two daughter cells each possessing the same genome as the parent cellAsexual Reproduction Reproduction in which all the offsprings genes are inherited from a single parent oEx Hydra and other microscopic animals by a simple buddy process or the propagation of plants from cuttingsSexual Reproduction Reproduction in which the offspring inherit genes from two parentsGamete A germ cell ovum or sperm that fuses with another to form a new organismIn order to keep the number of chromosomes constant from one generation to the next the gametes are usually Haploid Possessing half the usual complement of chromosomes Diploid Possessing the full complement of chromosomesMeiosis A pair of cell divisions that produces haploid gametes Gonad An organ that produces gametes a testis in males an ovary in femalesAll mammals produce by sexual reproduction Most vertebrates reproduce exclusively by sexual means Among invertebrate animals and plants many species can produce sexually or asexuallyRIVAL THEORIES OFFER EXPLANATIONS FOR SEXUAL REPRODUCTIONAdaptive Helping the propagation of an organisms genes An animal that reproduces asexually devotes all its resources to passing on its own genes and those genes are perpetuated in all of its descendants An animal that reproduces sexually dilutes its genes with those of another animal thus reducing the representation of its own genes in future generations Parthenogenesis A sexual reproduction from an unfertilized ovum virgin birthSexual Reproduction May Limit Harmful MutationsOne hypothesis suggests that sexual reproduction is adaptive because it helps organisms cope with the problem of harmful mutations
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