Asexual Reproduction

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Key Concept VOCABULARY Many organisms reproduce by cell division. asexual reproduction MAIN IDEAS binary fission Binary fission is similar in function to mitosis. Some eukaryotes reproduce through mitosis.

Connect to Your World In this flashy world of ours, you may think that the humble bacterium would have little chance of finding a mate. No dazzling smile, no fancy hair products, no shiny car, and—if we are brutally honest—not even a brain. With all of these limitations, it may seem that our bacteria friends would be destined to die out. And yet, bacteria are found in abundance and live just about everywhere on Earth. How can there be so many bacteria?

Main Idea Binary fission is similar in function to mitosis. Reproduction is a process that makes new organisms from one or more parent organisms. It happens in two ways—sexually and asexually. Sexual reproduction involves the joining of two specialized cells called gametes (eggs and sperm cells), one from each of two parents. The offspring that result are genetically unique; they have a mixture of genes from both parents. In contrast, asexual reproduction is the production of offspring from a single parent and does not involve the joining of gametes. The offspring that result are, for the most part, genetically identical to each other and to the single parent. Binary Fission and Mitosis Most prokaryotes reproduce through VISUAL VOCAB CONNECT TO binary fission (BY-nuh-ree FIHSH- Binary fission is the asexual reproduc- Cell Structure uhn), the asexual reproduction of a tion of a single-celled organism by Recall from the chapter Cell single-celled organism by which the division into two roughly equal parts. Structure and Function that cell divides into two cells of the same many scientists hypothesize that parent cell mitochondria and chloroplasts size. Binary fission and mitosis have were originally free-living similar results. That is, both processes prokaryotes. One piece of form two daughter cells that are DNA duplicates evidence that supports this genetically identical to the parent cell. hypothesis is the fact that these cell begins to divide two organelles replicate much as However, the actual processes are bacteria do, through fission. different in several important ways. daughter cells As you already learned, prokaryotes such as bacteria do not have nuclei. They also do not have spindle fibers. And although they have DNA, prokaryotes have much less DNA than do most eukaryotes. The DNA of most bacteria is in the form of a single circular chromosome.

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©Dr. Gopal Murti/Photo Researchers, Inc. Summarize separation into two daughter cells. formswall two the chromosomes, between which completes the undergoes cytokinesis. The membrane pinches inward, and cell anew away from each other. When is cell about the its twice size, original it membrane. As grows cell the and gets longer, chromosomes the move chromosome is copied. chromosomes Both are attached to cell the to attract mates. Organisms that reproduce do not asexually have costs. these amatefind but many also structures, and signals, behaviors that have evolved attract amate. This effort involves not only to and time the needed energy females canoffspring. bear In addition, reproducing sexually organisms must ism reproduces sexually, having five females and five males, only five the asexually, ten offspring all can have offspring of own. their If other the organ- Suppose two organisms each have ten offspring. If one organism reproduces For example, reproducing asexually all organisms can potentially reproduce. more efficient; rather, associated the costs reproduction of sexual are greater. chancethe that inchanging some individuals survive will conditions. off. In contrast, reproduction sexual increases genetic diversity, which raises tothem reproduce inachanged environment, entire the population could die ment same inthe way. If population members lack traits that enable conditions. identical offspring Genetically respond will to environ the - more than harmful helpful. In other words, ifit ain’t broke, don’t it. fix arethey well suited to environment, the genetic variation could be that reproduction asexual results ingenetically identical offspring. If reproduction more can be reproduction. efficient than sexual Recall situation. In favorable environments that do not change much, asexual Very often, something whether is helpful or dependson harmful the Advantages Disadvantages and Asexual of Reproduction Keep inmind, however, that ofreproduction act the asexual itself is not However, reproduction asexual may adisadvantage be inchanging Binary fission,Binary shown in 1

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