The Importance of Reproduction
Reproduction, the process of producing offspring by sexual or asexual means, is possibly the only life processes necessary for the survival of a species rather than the survival of an organism. Sexual reproduction, common in mammals, amphibians, birds and other classes of animals, allows for the creation of genetically varied organisms with the combination of chromosomes from two parent organisms through meiosis and fertilization. Sexual reproduction, therefore, also allows for evolution as advantageous traits are passed on to future generations by natural selection (as adaptations, in the form of mutations, often do), and inferior traits disappear. Asexual reproduction, however, found in bacteria, sponges and some starfish allows for the creation of genetically identical organisms with the replication of DNA from one parent organism through mitosis. There are four types of asexual reproduction: binary fission (the replication of DNA followed by cell division as performed by prokaryotes, bacteria), budding (the branching off and growth of offspring from the parent organism, as performed by hydra), fragmentation (the formation of offspring from a detached piece of the parent organism, as performed by sponges), and vegetative propagation (the growth of multiple plants from one parent organism, as performed by strawberry plants). Asexual reproduction allows for the creation of many offspring in short periods of time and allows organisms in isolation to create offspring independently, but it produces no genetic variability, creating actual clones and an environmental factor that kills one of a species will kill all of the species. |
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Mitosis vs. Meiosis
Mitosis is the replication of cells for asexual reproduction, growth and repair, in which the genetic material of a diploid cell is copied to form two identical diploid cells in four or five scientific phases. The phases are interphase, prophase, metaphase, anaphase, and telophase. Interphase is the non-dividing stage of the cell, when chromatin is visible, and DNA replication occurs. In prophase, replicated DNA is arranged into chromosomes, the nucleus dissolves, and spindle fibers form. During metaphase, the chromosomes align in the middle of the cell for equal distribution amongst daughter cells, as spindle fibers attach to the centromeres of each chromosome pair. In anaphase, the chromosomes divide, sister chromatids being pulled apart by the spindle fibers. During telophase, the cell membrane pinches inward, splitting the cytoplasm and forming two new identical cells, as the nucleus reappears and chromatids revert to chromatin form.
Meiosis, however, is the creation of gametes or sex cells for sexual reproduction, in which the genetic material of a diploid cell is copied to form four differing haploid cells in multiple scientific phases. Meiosis I is essentially composed of the same steps as in the stages of mitosis (prophase, metaphase, anaphase, and telophase), except that in prophase I crossing-over occurs and genetic information of alleles are exchanged between homologous pairs. Meiosis II is essentially composed of the same steps as in the stages of Meiosis I and mitosis (prophase, metaphase, anaphase, and telophase), except by the end of Meiosis II there are four differing haploid cells or gametes that are known as sperm and eggs in human males and females. For human males, meiosis only occurs after puberty in the testes, whereas for human females, meiosis occurs before birth in the ovaries.
Mitosis is the replication of cells for asexual reproduction, growth and repair, in which the genetic material of a diploid cell is copied to form two identical diploid cells in four or five scientific phases. The phases are interphase, prophase, metaphase, anaphase, and telophase. Interphase is the non-dividing stage of the cell, when chromatin is visible, and DNA replication occurs. In prophase, replicated DNA is arranged into chromosomes, the nucleus dissolves, and spindle fibers form. During metaphase, the chromosomes align in the middle of the cell for equal distribution amongst daughter cells, as spindle fibers attach to the centromeres of each chromosome pair. In anaphase, the chromosomes divide, sister chromatids being pulled apart by the spindle fibers. During telophase, the cell membrane pinches inward, splitting the cytoplasm and forming two new identical cells, as the nucleus reappears and chromatids revert to chromatin form.
Meiosis, however, is the creation of gametes or sex cells for sexual reproduction, in which the genetic material of a diploid cell is copied to form four differing haploid cells in multiple scientific phases. Meiosis I is essentially composed of the same steps as in the stages of mitosis (prophase, metaphase, anaphase, and telophase), except that in prophase I crossing-over occurs and genetic information of alleles are exchanged between homologous pairs. Meiosis II is essentially composed of the same steps as in the stages of Meiosis I and mitosis (prophase, metaphase, anaphase, and telophase), except by the end of Meiosis II there are four differing haploid cells or gametes that are known as sperm and eggs in human males and females. For human males, meiosis only occurs after puberty in the testes, whereas for human females, meiosis occurs before birth in the ovaries.
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The Reproduction of The Morning Sun Star
The Morning Sun Star, like all other starfish, has the ability to reproduce asexually through regeneration/fragmentation to create genetically identical offspring, but its preferred method is to reproduce sexually through spawning to create genetically diverse offspring. From March to June the gonads, the sexual organs of starfish, fill up with oocytes or eggs in the females and sperm in the males and the starfish spawn in groups, releasing/depositing their gametes in large numbers into the water to increase the chance of fertilization. [1] Once the eggs are fertilized, the Morning Sun Stars sometimes hold onto the zygotes until they hatch, sitting on them, creating a brooding basket or keeping them in between their rays. When the zygote/egg structure hatches, the larval form of the Morning Sun Stars is left adrift in the water to search for food, grow and develop into a juvenile starfish and then into a full grown starfish. At approximately two years old, the offspring is considered a full grown starfish and can begin to reproduce itself. [2]
The Morning Sun Star, like all other starfish, has the ability to reproduce asexually through regeneration/fragmentation to create genetically identical offspring, but its preferred method is to reproduce sexually through spawning to create genetically diverse offspring. From March to June the gonads, the sexual organs of starfish, fill up with oocytes or eggs in the females and sperm in the males and the starfish spawn in groups, releasing/depositing their gametes in large numbers into the water to increase the chance of fertilization. [1] Once the eggs are fertilized, the Morning Sun Stars sometimes hold onto the zygotes until they hatch, sitting on them, creating a brooding basket or keeping them in between their rays. When the zygote/egg structure hatches, the larval form of the Morning Sun Stars is left adrift in the water to search for food, grow and develop into a juvenile starfish and then into a full grown starfish. At approximately two years old, the offspring is considered a full grown starfish and can begin to reproduce itself. [2]