sex or no sex - SexandnoSex The whys of Sex...

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Sex and no Sex The why’s of Sex
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So, what is sex? What is gender? Sex is recombination, plus outcrossing (Ridley) So sex can be any process that results in exchange of genetic matter and may not involve reproduction, as we will see later. In fact, sometimes recombination is not involved either. Gender is biologically determined by which gamete retains intracellular organelles when the gametes merge. One gender (usually called female) retains the organelles while the other (usually called male) contributes only the nucleus and not organelles. We will examine gender in more detail later in the course, including creatures with hundreds of genders as well as its social constructs in humans.
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Male gamete vs Female gamete Only the nucleus from the sperm enters the ovum, so by definition the sperm is male, the ovum female
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When is Sex really Sex? Sex is a mechanism that results in recombination. There can be recombination without sex, however. One key issue is whether the offspring are identical to the parent(s) or not.
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So, why have sex?  Why not? As you will recall from “The Red Queen” there is no completely satisfactory answer to the question of why organisms have sex. Nevertheless, there are hypotheses that approach explanations and we will review some of these in this portion of the class. Asexual organisms can reproduce and spread much faster than sexual organisms. Sex increases variation, which provides resistance to stresses such as diseases, but at a “cost.”
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Asexual and Sexual Reproduction Asexual reproduction is based on mitosis ; offspring produced asexually are genetically identical to one another and to their parent. Sexual reproduction is based on meiosis . Genetic recombination during meiosis and the fusion of haploid gametes from different parents during fertilization result in offspring that are genetically different from one another and from their parents.
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Advantages of Asexual Reproduction Reproduction is always available Energetically efficient because there is no need to search for a partner There is no sexual selection and no competition for sex partners If the organism is in an environment that is conducive to their survival, the offspring should be successful because they are genetically fit Likewise, effective traits are not being diluted by breeding
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Disadvantages of Asexual Reproduction Undesirable traits are maintained rather than being eliminated by interbreeding Desirable traits are selected for rather slowly Lack of variation lowers the ability of the individuals in a population to respond to changes in the environment, so populations or species can be quickly decimated and lost.
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This note was uploaded on 02/17/2011 for the course BIOLOGY 120 taught by Professor Fink during the Winter '11 term at University of Michigan.

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sex or no sex - SexandnoSex The whys of Sex...

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