Meiosis Cell Division And Dna Replication Biology

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In this experiment we observed the procedure of miosis by looking at different slides. Meiosis is a procedure in which a diploid ( 2n ) parent cell is divided into four haploid ( n ) girl cells. The girl cells have half the figure of chromosomes as the parent cell. Meiosis chiefly occurs in sex cells ( gametes ) of worlds through the procedure of spermatogenesis ( males ) or oogenesis ( females ) . It is indispensable for sexual reproduction, and therefore is seen in all eucaryotes that reproduce sexually. Before the cell undergoes miosis, it foremost replicates its DNA. Meiosis includes 2 rhythms of division- miosis I and miosis II. After miosis I is completed, DNA is non replicated, which leads to the concluding girl cells being haploid ( n ) . The first measure of miosis I is prophase I. During prophase I, Deoxyribonucleic acid can be exchanged between homologous chromosomes by fours “ traversing over ” , a procedure referred to as recombination. The new combination of DNA provides for familial fluctuation for the girl cells. In add-on, in prophase I, the atomic envelope disintegrates, and the two centrioles move to opposite terminals of the cell. In metaphase I, homologous chromosomes are aligned at the metaphase home base ( site where the cell will split ) in brace. The side at which homologous braces will lineup is random and farther improves the opportunities for familial fluctuation. The centrioles attach centromere microtubules to the chromosomes, so that they can be pulled apart to the different terminals as the cell divides. In anaphase I, the microtubules shorten, drawing the brace of homologous chromosomes apart from one another. In telophase I, the chromosomes arrive at their several terminals and the cell divides to organize two monoploid cells. The atomic membrane is reformed, and the microtubules disappear. The chromosomes uncoil back into chromatin. Note, that even though the first meiotic division led to two haploid cells, each chromosome still contains a brace of sister chromatids. Therefore, miosis II begins without DNA retroflexing beforehand. The stairss in miosis II are really similar to the 1s in miosis I. In prophase II, the atomic envelope disintegrates, the centrioles move to the opposite terminal of the pole, the chromosomes condense and fix for the 2nd division. In metaphase II, the chromosomes once more line up indiscriminately at the home base, but this clip independently, non in braces. The spindle web is formed is besides formed. In anaphase II, the sister chromatids are pulled apart and travel toward the opposite terminals of the pole. Last, in telophase II, the cells are cleaved and the atomic envelope reappears. The chromosomes uncoil and the terminal consequence is 4 monoploid girl cells. In spermatogenesis, the 4 girl cells are the spermatids. However, in oogenesis, even though 4 monoploid girl cells are created, 3 are polar organic structures, while the last is an ootid ( egg ) , which might be fertilized by a spermatid. During fertilisation ( when the spermatid and ootid articulation ) , the figure of chromosomes reverts back to 2n ( diploid ) . The random alliance and crossing over are really of import to the procedure of miosis because they provide for greater genotypic diverseness. However, if the chromosomes are non able to divide, several mistakes can originate. Klinefelter and Turner syndromes are due to nondisjunction, during which there is an excess X chromosome nowadays in males, or losing an Ten chromosome in females, severally ( Russell, 346-349 ) . We besides observed the life rhythm of the insect Drosophila melanogaster. We will be experimenting on them in the approaching hebdomads. This insect serves as a great experimental being in the field of genetic sciences due to its short, alone life rhythm, and since Mendel ‘s Torahs of heritage ( jurisprudence of segregation, jurisprudence of independent mixture ) are clearly seeable when they mate. The jurisprudence of segregation provinces that when any single produces gametes, the transcripts of a cistron separate so that each gamete receives merely one transcript. The jurisprudence of independent mixture provinces that allelomorphs of different cistrons assort independently from each other during gamete formation. The intent of this experiment was to familiarise ourselves with the procedure of miosis and the insect Drosophila melanogaster, as we will be working with them in future experiments. We used slides from human testicle, rat testicle, and chorthippus testicle, to compare the procedure of miosis in different eucaryotes. I predict that I will be able to see the phases of prophase, metaphase, anaphase and telophase in the slides.


I believe that the procedure of miosis will be the same in all three eucaryotes, and I will be able to see the cells differentiating.

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I should be able to see the different constructions of the insects and be able to separate male and female Drosophila melanogasters based on their visual aspect.

I believe that I will be able to witness the different phases of miosis in the slides.


Obtain the slides and the compound light microscope from the teacher. Put the first slide on the phase of the microscope ( the microscope should be on the lowest power- 40x ) and utilize the harsh accommodation boss to concentrate the slide. Turn to the following highest power ( 100x ) , and this clip, usage merely the all right accommodation boss to convey the slide into focal point. Turn the microscope to the 400x power, and once more concentrate the slide. Sketch what you see on a separate sheet of paper and label the different constructions. Before traveling on to the oil submergence power, put a small bead of oil in the center of the slide. Concentrate the image under oil submergence and chalk out the consequences one time once more. After you ‘re done chalk outing the slide, lower the phase and put the microscope back to the lowest power ( Caution: be careful non to acquire oil on the 400x power when turning the aims as this will destroy the lens ) . Repeat these stairss for the remainder of the slides ( Note: for the Drosophila melanogaster male and female slide, the lowest power, 40x, is good plenty to acquire a good overview ) . The slides we viewed were: chorthippus testicle, generalized animate being cell, human chromosome ( metaphase province ) , turtle liver chondriosome, drosophila chromosome, Drosophila melanogaster ( male and female ) , rat testicle, and human testicle. At the terminal of the experiment, clean all the slides that have oil on them, wipe the oil submergence lens, and return the stuffs to the teacher.


Drawings- See Attached Documents


1. What major chromosomal event occurs between leptonema and zygonema?

Between leptonema and zygonema, the major chromosomal event that occurs is the coupling of the homologous chromosomes.

2. Make any of the chromosomes at zygonema appear to dwell of two analogue parts? A How make you account for this visual aspect?

Yes, chromosomes at zygonema appear to dwell of two parallel parts, which is likely due to the mated homologues.

3. Consult your text edition for a definition of the term chromomere. A Can you observe chromomeres in any of the meiotic cells you are analyzing? At what substages of prophase I are chromomeres apparent?

Chromomeres are dark parts of chromatin condensation. Yes, you can observe chromomeres in meitotic cells ; they are normally seen in zygonema of prophase I.

4. Make you detect a big, darkly staining construction in the karyon during leptonema and zygonema? This organic structure represents an already extremely condensed ( heterochromatic ) X chromosome. Can you follow the destiny of this chromosome through the remainder of the substages of prophase I and metaphase I?

Yes, it should be possible to follow the destiny of this chromosome through the remainder of the substages of prophase I and metaphase I. This Ten chromosome will non aline with the remainder of the chromosomes at the metaphase home base and will be near one terminal of the splitting cell or the other.

5. A Briefly list major differences between zygonema and pachynema.

At zygonema, the chromosomes are much less condensed than those at pachynema. Traversing over occurs at pachynema. The figure of chromosomes can be determined at pachynema, but non at zygonema.

6. Locate cells in diplonema. A Can you detect a ) the two homologous chromosomes in a brace? B ) single chromatids in a chromosome? degree Celsius ) decussation?

a ) Yes, the homologous chromosomes in braces are seeable. B ) Yes, the chromatids are besides seeable, since the chromosomes at this phase are much coiled. degree Celsius ) Yes, the decussation is seeable, it is the point where the brace of homologous chromosomes exchange familial stuff.

7. Because of the grade of condensation of the chromosomes, diakinesis is an ideal phase at which to find the chromosome figure. A Count the chromosomes in a grasshopper cell at diakinesis. Record the figure here. A Does this stand for the diploid figure? Justify your reply.

Note that sex in grasshoppers is determined by an XO mechanism in which the female is XX, but the male has a individual X chromosome. A Therefore, the X chromosome that you observe in diakinesis is non a four. What is the significance of this information for finding chromosome figure in grasshopper males versus females?

Since grasshopper males are losing an X chromosome, to happen their diploid figure of chromosomes, one would hold to number the monoploid figure ( n ) , dual it ( 2n ) , but so deduct 1, since it is losing an Ten chromosome. In females, the minus will non be necessary ; they will ever hold dual their monoploid figure of chromosomes ( example- if monoploid figure peers 14 chromosomes, male diploid figure will be ( 2n-1 = 28-1 ) 27 chromosomes, while the females will hold 28 chromosomes in a diploid cell ) .

8. Detect several cells in metaphase I. Make you detect a chromosome in an unusual place with regard to the other chromosomes in the cell? What chromosome might this be?

Yes, this chromosome could be the X or Y chromosome.

9. Can you happen cells in other phases of miosis or sperm distinction? A If so, briefly describe their visual aspect and province what stages you think they might be.

Yes, it is possible to happen other phases of miosis. In metaphase, the chromosomes are lined up at the metaphase home base. In anaphase, the chromosomes are being pulled apart, and in telophase the cells should be dividing via cytokinesis.


The procedure of miosis is really complicated, but is necessary for sexual reproduction. There are five substages of prophase I in miosis. Prophase I is the most of import phase in miosis, since this is the phase where crossing over occurs between homologous braces of chromosomes, which is indispensable for familial fluctuation. The first substage is leptonema where chromosomes get down to distill into long strands and get down to look for their homologous brace. In the 2nd substage, zygonema, the chromosomes have found their braces. The 3rd substage, pachynema, is where traversing over occurs. In add-on, the chromosomes are condensed plenty so that one can number the figure of chromosomes. In the 4th substage, diplonema, parts of the chromosome Begin to divide, and the decussation ( the site where crossing over takes topographic point ) is made seeable. The last phase, diakenisis, is where the nucleoli disappears, the atomic membrane disintegrates, and the four fours of a brace of homologous chromosomes are clearly seeable ( the chromosomes are to the full condensed ) ( Meiosis Prophase I ) .

When looking at the Drosophila melanogaster, males were easy distinguishable from females. Males were smaller in size compared to the females. The terminal of the male was more rounded, while the female was pointier. Females had more of a stripy form on their terminals, while males have black as the dominant colour. Last, males have a sex comb at the articulation of each forepart leg ( males besides have a phallus ) ( Hammersmith & A ; Mertens, 5 ) .

In the generalised animate being cell, I was able to place the karyon and the atomic envelope. In the human chromosome slide of metaphase, the chromosomes were lined up, which means they were about to be separated. In the human, rat and chorthippus testicle, I had a hard clip placing the different cell types, or cells in different stages of miosis. Meiosis is an indispensable procedure, and if an mistake occurs, the effects could be deadly.

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