Diploid versus Haploid | BioNinja
Meiosis is where a diploid cell gives rise to haploid cells, and fertilization is and the gametophyte and the relationship between them vary among species. Diploid cell are somatic; your body. Haploid cells are germ line; gametes. Diploid cells have the full 23 pairs of chromosomes. Haploid means. Feb 16, Germ cells have only half the number of chromosomes as a diploid cell one of each pair - and are termed haploid (n). In a human egg or sperm.
The spindle fiber disassembles and the nucleus reforms. This is quickly followed by cytokinesis and the formation of two haploid cells, each with a unique combination of chromosomes, some from the father and the rest from the mother.
Meiosis II is essentially the same as mitosis, separating the sister chromatids from each other. Once again the nucleus breaks down, and the spindle begins to reform as the centrioles move to opposite sides of the cell. The spindle fibers align the 23 chromosomes, each made out of two sister chromatids, along the equator of the cell.
The sister chromatids are separated and move to opposite poles of the cell. As the chromatids separate, each is known as a chromosome. Anaphase II results in a cell with 23 chromosomes at each end of the cell; each chromosome contains half as much genetic material as at the start of anaphase II.
The nucleus reforms and the spindle fibers break down. Each cell undergoes cytokinesis, producing four haploid cells, each with a unique combination of genes and chromosomes. Meiosis is a process in which a diploid cell divides itself into four haploid cells.
Meiosis and Genetic Variation Sexual reproduction results in infinite possibilities of genetic variation. This occurs through a number of mechanisms, including crossing-over, the independent assortment of chromosomes during anaphase I, and random fertilization.
Crossing-over occurs during prophase I. Crossing-over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. Recall during prophase I, homologous chromosomes line up in pairs, gene-for-gene down their entire length, forming a configuration with four chromatids, known as a tetrad.
Diploid vs Haploid: Similarities and Differences | victoryawards.us
At this point, the chromatids are very close to each other and some material from two chromatids switch chromosomes, that is, the material breaks off and reattaches at the same position on the homologous chromosome Figure 5. This exchange of genetic material can happen many times within the same pair of homologous chromosomes, creating unique combinations of genes. This process is also known as recombination.
A maternal strand of DNA is shown in red. Paternal strand of DNA is shown in blue. Crossing over produces two chromosomes that have not previously existed. The process of recombination involves the breakage and rejoining of parental chromosomes M, F. As mentioned above, in humans there are over 8 million configurations in which the chromosomes can line up during metaphase I. It is the specific processes of meiosis, resulting in four unique haploid cells, that results in these many combinations.
Figure 6 compares mitosis and meiosis. This independent assortment, in which the chromosome inherited from either the father or mother can sort into any gamete, produces the potential for tremendous genetic variation. Together with random fertilization, more possibilities for genetic variation exist between any two people than individuals alive today. Sexual reproduction is the random fertilization of a gamete from the female using a gamete from the male.
A sperm cell, with over 8 million chromosome combinations, fertilizes an egg cell, which also has over 8 million chromosome combinations.
Meiosis ‹ OpenCurriculum
That is over 64 trillion unique combinations, not counting the unique combinations produced by crossing-over. In other words, each human couple could produce a child with over 64 trillion unique chromosome combinations. Mitosis produces two diploid daughter cells, genetically identical to the parent cell.
Meiosis produces four haploid daughter cells, each genetically unique. Gametogenesis At the end of meiosis, haploid cells are produced. These cells need to further develop into mature gametes capable of fertilization, a process called gametogenesis Figure 7.
Gametogenesis differs between the sexes. In the male, the production of mature sperm cells, or spermatogenesis, results in four haploid gametes, whereas, in the female, the production of a mature egg cell, oogenesis, results in just one mature gamete.
Analogies in the process of maturation of the ovum and the development of the spermatids. Four haploid spermatids form during meiosis from the primary spermatocyte, whereas only 1 mature ovum, or egg forms during meiosis from the primary oocyte. Three polar bodies may form during oogenesis. These polar bodies will not form mature gametes. During spermatogenesis, primary spermatocytes go through the first cell division of meiosis to produce secondary spermatocytes.
These are haploid cells.
Secondary spermatocytes then quickly complete the meiotic division to become spermatids, which are also haploid cells. The spores will then develop into the multicellular gametophytes. Example of alternation of generations: Haploid 1n spores germinate and undergo mitosis to produce a multicellular gametophyte 1n. Specialized cells of the gametophyte undergo mitosis to produce sperm and egg cells 1nwhich combine in fertilization to make a zygote 2n.
The zygote undergoes mitosis to form a multicellular, diploid sporophyte, the frond-bearing structure that we usually think of as a fern. On the sporophyte, specialized structures called sporangia form, and inside of them, haploid cells spores, 1n are formed by meiosis. The spores are released and can germinate, starting the cycle over again. Although all sexually reproducing plants go through some version of alternation of generations, the relative sizes of the sporophyte and the gametophyte and the relationship between them vary among species.
In plants such as moss, the gametophyte is a free-living, relatively large plant, while the sporophyte is small and dependent on the gametophyte.
In other plants, such as ferns, both the gametophyte and sporophyte are free-living; however, the sporophyte is much larger, and is what we normally think of as a fern. In seed plants, such as magnolia trees and daisies, the sporophyte is much larger than the gametophyte: The gametophyte is made up of just a few cells and, in the case of the female gametophyte, is completely contained inside of the sporophyte within a flower.
Why is sexual reproduction widespread? In some ways, asexual reproduction, which makes offspring that are genetic clones of the parent, seems like a simpler and more efficient system than sexual reproduction. In addition, asexual reproduction only calls for one individual, removing the problem of finding a mate and making it possible for an isolated organism to reproduce.
Despite all this, few multicellular organisms are completely asexual.
What is the relationship between diploid cells and haploid cells?
Why, then, is sexual reproduction so common? This question has been hotly debated, and there is still disagreement about the exact answer.
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The processes that generate genetic variation in all sexual life cycles are: Why is this genetic variation a good thing? Sexual reproduction continually makes new, random combinations of gene variants. This makes it more likely that one or more members of a sexually reproducing population will happen to have a combination that allows survival under the new conditions e. Over generations, beneficial gene variants can spread through the population, allowing it to survive as a group under the new conditions.
This article is a modified derivative of the following articles: Download the original article for free at http: Retrieved October 15, from Wikipedia: Retrieved July 24, from Wikipedia: Many protists reproduce by mitosis until their environment deteriorates, then they undergo sexual reproduction to produce a resting zygotic cyst. Meiosis produces 4 haploid cells. Mitosis produces 2 diploid cells. Meiosis I reduces the ploidy level from 2n to n reduction while Meiosis II divides the remaining set of chromosomes in a mitosis-like process division.
Most of the differences between the processes occur during Meiosis I. The above image is from http: Synapsis is the process of linking of the replicated homologous chromosomes.
The resulting chromosome is termed a tetradbeing composed of two chromatids from each chromosome, forming a thick 4-strand structure. Crossing-over may occur at this point.
During crossing-over chromatids break and may be reattached to a different homologous chromosome. The alleles on this tetrad: This doubles the variability of gamete genotypes.
The occurrence of a crossing-over is indicated by a special structure, a chiasma plural chiasmata since the recombined inner alleles will align more with others of the same type e. Near the end of Prophase I, the homologous chromosomes begin to separate slightly, although they remain attached at chiasmata. Crossing-over between homologous chromosomes produces chromosomes with new associations of genes and alleles.