100C Reproductive System - Reproduction Modes of...

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Unformatted text preview: Reproduction Modes of Reproduction Asexual Sexual 1) no fusion of gametes; 1) fusion of gametes, all genes from one egg (ovum) & sperm parent = fertilization; ½ of genes from each parent Includes fission, spores budding, fragmentation parthenogenesis 2) Progeny genetically 2) progeny genetically identical dissimilar to each other and parents 3) Organisms can 3) better adaptability reproduce without to changing environment Modes of Asexual Reproduction Fission Paramecium Anthopleura Dugesia Budding Hydra Saccharomyces Fragmentation Marchantia Linckia Spores Ulothrix Parthenogenesis—development of an egg without fertilization— Organisms that are haploid produce their eggs without meiosis Lizards ( Cnemidophorus) constitute an all female population. Behave as female or male in response to hormone cycle. High estrogen elicits female behavior prior to ovulation. Post ovulation signals a drop in estrogen, and elicits male behavior. One mounts the other as stimulus for ovulation. In this case, organisms are diploid, and offspring are diploid because of chromosome doubling in the egg following meiosis. Other—Male drone bees, rotifers Switching Reproductive Modes: A Case History • Many animal species regularly switch between reproducing asexually and sexually. • For example, Daphnia are crustaceans that reproduce both asexually and sexually in a typical year. • Throughout the spring and summer, Daphnia produce only diploid female offspring by parthenogenesis. • In late summer/early fall, however, many females begin producing male offspring. • Haploid sperm from these males fuse with haploid eggs that females produce by meiosis during fertilization . • In spring, the sexually produced offspring hatch and begin reproducing asexually. • Daphnia were shown to require three different cues from the environment to switch to sexual reproduction: crowding, low food availability, and short day lengths. • Scientists hypothesize that genetically variable offspring have higher fitness in rapidly changing environments. Daphnia produce diploid eggs asexually. Brood pouch with eggs External Fertilization • Most animals that rely on external fertilization live in aquatic environments and tend to produce huge numbers of gametes. • Gamete release for external fertilization must be coordinated. • Most research to date indicates that gametogenesis occurs in response to environmental cues such as lengthening days and warmer water temperatures, which indicate a favorable season for breeding. • Research is ongoing into what synchronizes gamete release. The chemical messengers called pheromones might be involved. Internal Fertilization and Sperm Competition • Internal fertilization occurs in the vast majority of terrestrial animals and in a significant number of aquatic animals....
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This note was uploaded on 03/06/2011 for the course BIOL 100C taught by Professor Barbaraveno during the Spring '08 term at California State University Los Angeles .

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100C Reproductive System - Reproduction Modes of...

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