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| Image/Video Creator | James R LaFountain Jr. (University at Buffalo, Buffalo, NY), Rudolf Oldenbourg (Marine Biological Laboratory, Woods Hole, MA) |
| Important Concept | During the second meiotic division (meiosis II), the two daughter cells resulting from meiosis I enter into cell division without undergoing DNA replication. |
| What should I look for? | Following telophase I, the cells enter a brief interkinesis (a period between cell divisions) characterized by an absence of DNA replication. This stage is followed by prophase II, where this video begins. Nuclei can be seen briefly, followed by nuclear envelope breakdown and penetration of microtubules into the former nuclear space. During metaphase II, the individual chromatids of dyad chromosomes attach to microtubules emanating from opposite poles of the cell, thus facilitating the separation of the chromatids into the daughter cells. Note that the spindles of meiosis II (and the resulting cell divisions) form at approximately right angles to the spindle of meiosis I. Meiosis II concludes with telophase II and cytokinesis, resulting in four haploid daughter cells, each of which is genetically distinct.
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| How was it done? | Insect spermatocytes like those from Nephrotoma suturalis (crane fly) that were used here have been ideal model systems for cytological studies of meiosis. First, spermatocytes from a number of insect species are found in testes unconnected to each other or to any other types of connective tissue cells. Thus, they are 'free floating, ' unlike spermatocytes in 'solid' human testes. That feature makes them easy to culture and spread on a microscope coverslip. The karyotype (a display of the full set of chromosomes of a cell with respect to size, shape and number) of crane flies is very simple - diploid is only eight chromosomes - and thus for the study of individual chromosomes in meiosis I, crane fly spermatocytes are ideal. In addition, meiosis I lasts only 4 hours, followed by a brief interkinesis, which is followed by meiosis II lasting only 3 hours. Thus, all events of meiosis can be observed in an individual cell over the course of 5 to 7 hours, well within the life-span of spermatocytes. Lastly, crane flies can be maintained in the laboratory year-round, providing the cell biologist with a ready supply of material whenever needed.
See 'Meiosis I: First Meiotic Division' at http://cellimages.ascb.org/u?/p4041coll12, 209 for experimental details, including information on the microscope that was used to film these videos.
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| Why is this important? | Meiosis results in the reassortment and recombination of genetic material between parental DNA molecules such that every germ cell generated contains a unique combination of genes. Upon fertilization, this guarantees that every individual of a species will have a unique genetic composition - a key factor in assuring the genetic diversity of the species. The products of meiosis II are cells with a haploid DNA complement. |
| Points to ponder | What are polar bodies? How does meiosis during spermatogenesis (creation of a sperm cell, the male gamete) differ from meiosis during oogenesis (creation of an egg cell, the female gamete)?
What happens following meiosis II to generate mature ova and spermatozoa?
Go to http://www.pbs.org/wgbh/nova/baby/divide.html# for a step-by-step comparison between meiosis and mitosis.
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| Advanced Material | LaFountain JR Jr, Oldenbourg R. Meiosis in a living crane fly spermatocyte: meiosis I still images. ASCB Image & Video Library. February 2007:NUC-7. Available at: http://cellimages.ascb.org/u?/p4041coll12,98
LaFountain JR Jr, Oldenbourg R. Meiosis I in a living crane fly spermatocyte: time lapse movie. ASCB Image & Video Library. February 2007:VID-13. Available at: http://cellimages.ascb.org/u?/p4041coll12,105
LaFountain JR Jr, Oldenbourg R. Meiosis in a living crane fly spermatocyte: meiosis II time lapse movie. ASCB Image & Video Library. February 2007:VID-14. Available at: http://cellimages.ascb.org/u?/p4041coll12,106
Definitions (hit your browser's back button to return to the IVL):
chromatid: http://en.wikipedia.org/wiki/Chromatid
chromosome: http://en.wikipedia.org/wiki/Chromosome
cytokinesis: http://en.wikipedia.org/wiki/Cytokinesis
DNA replication: http://en.wikipedia.org/wiki/DNA_replication
dyad: http://en.wikipedia.org/wiki/Dyad_%28biology%29
haploid: http://en.wikipedia.org/wiki/Ploidy
interkinesis: http://en.wikipedia.org/wiki/Interkinesis
karyotype: http://en.wikipedia.org/wiki/Karyotype
microtubule: http://en.wikipedia.org/wiki/Microtubule and http://cellbio.utmb.edu/cellbio/microtub.htm
meiosis: http://en.wikipedia.org/wiki/Meiosis
Nephrotoma suturalis: http://en.wikipedia.org/wiki/Crane_fly
oogenesis: http://en.wikipedia.org/wiki/Oogenesis
polarizing microscope: http://www.microscopyu.com/articles/polarized/polarizedintro.html
polar body: http://en.wikipedia.org/wiki/Polar_body
spermatogenesis: http://en.wikipedia.org/wiki/Spermatogenesis
spindle apparatus: http://en.wikipedia.org/wiki/Spindle_apparatus
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| Title | 1. Teaching Item. Meiosis II: Second Meiotic Division |
| Annotator(s) | David L Ennist (The American Society for Cell Biology, Bethesda, MD) |
| Citation | Ennist DL. Meiosis II: Second Meiotic Division. ASCB Image & Video Library. 2007;EDU-7. Available at: http://cellimages.ascb.org/u?/p4041coll12,213 |
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| Publication Date | Published in October 2007. |
| License Details | Terms for non-commercial use: http://cellimages.ascb.org/cdm4/terms.php
For commercial use contact us at: cellimages@ascb.org. |
| Publisher | The American Society for Cell Biology |
