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7

The frequency rises with maternal age due to a peculiarity of meoisis in female mammals. Meiosis is originated in the fetal ovary, arresting at metaphase I with the homologous chromosomes aligned for segregation. Cells remain in this state until the time of ovulation, often decades later in humans. The longer cells remain in the arrested ...


7

This is a venerable fact. Exceptions in D. melanogaster strain Y-007 have been observed and D. ananassae has consistent male cross-overs, but this work dates back to the 1970s. This Current Biology 2002 paper is not exactly new, but sheds some light on the issue in question. In male Drosophila melanogaster, meiosis occurs in the absence of ...


6

If the question is about the one and only most important difference between mitosis and meiosis, then the answer "meiosis reduces ploidy" is probably correct. But if the list of important differences is open, it would be critical to add that mitosis generates identical cells (identical to each other and any ancestral cells, barring rare new mutations), while ...


5

Primary oocytes are formed prenatally and reain suspended in prophase of meiosis I for years until the onset of puberty. An oocyte completes meiosis I as its follicle matures (during ovulation) resulting in a secondary oocyte and the FIRST polar body. After ovulation, each oocyte continues to metaphase of meiosis II. Meiosis II is completed only if ...


5

I'm actually not sure myself. If I were to use something, I would go with "Mitos'd" and "Meios'd". However, you may not win over many fans, depending on the audience. If it's with students or maybe a professor, you could get away with shortening the processes. If it's in any formal setting, be as precise and descriptive as possible. It's not a lot of ...


4

To the best of my knowledge there is no strong evidence as to the reason why. The most reasonable explanation seems to be that it evolved as a crude mechanism for preventing recombination of the male sex-chromosome. You might then ask why a mechanism targeted to the sex-chromosome specifically (as in humans) did not evolve to which I'd suggest that ...


4

No, meiosis is not a cycle like mitosis. In mitosis, haploid or diploid cells divide to create two genetically identical cells, and this process can go on and on. On the other hand, meiosis results in 4 genetically unique daughter cells which are also haploid. If a haploid cell was to try to undergo meiosis, there would not be enough genetic material and you ...


4

In automixy the meiotic cells give rise to diploid offsprings. This can happen by diploidization of the haploid cell (1n->2n), which will produce homozygotes or endomitosis prior to meiosis (4n->2n) which produces heterozygotes. Examples: Cnemidophorus uniparens : 4n->2n Sphyrna tiburo: 1n->2n I don't know of any case where there is fusion ...


3

Trisomy is due to non-disjunction in meiosis (the process in which eggs and sperm are created). This happens before fertilization. Trisomies are more frequently seen in children of older women. It's not fully understood why this happens, but it is likely related to the fact that the oocytes do not complete meiosis (and become eggs) until ovulation. Here's ...


3

The paper you cite says that the break points are single stranded DNA which have specific proteins bound to them. I'm not an expert here, but if thats the cause of meitotic break points there are some interesting possibilities for detecting them: you could detect them with a tiling array. - that's an micro array which has an oligomer every 40 bp or so ...


3

When females are in their mother's womb all their Oogenium (plural Oogenia) are being made, they they undergo mitotic divisions to become a primary oocyte. Then, the primary oocytes start to undergo meiosis I - but meiosis I is arrested. This is the first meiotic arrest. When does meiosis I continues? when a female hits puberty, every month one or more ...


3

Meiosis consists of two divisions. Both are somehow similar to "ordinary" type of cell division - mitosis, but there is no DNA replication between them. As mitosis, each of two meiosis divisions might be divided into 5 stages: Profaze (condensation of chromosomes, formation of microtubular spindle apparatus between two centrosomes) Prometaphase (the ...


2

According to all I've learned and heard, the only thing consistent about meiosis is that it reduces ploidy because homologous chromosomes are separated. (Not necessarily diploid to haploid - it can be polyploid as well, although odd ploidies usually seem to mess it up.) Mitosis on the other hand mainly serves to separate two copies of a genome into ...


2

As far as I can tell there is a distinction. A tetrad refers to the entire group of four chromatids after they have come together for crossing over in Prophase I (synapses). A synaptonemal complex as you would expect is formed in synapses. This is a protein-RNA complex that connects the intervening regions of matched chromosomes in some circumstances - ...


2

Meiosis starts with a diploid cell and produces four haploid cells. In animals, the starting diploid cell is usually called a germ cell and the surviving haploid cells become gametes (sperm and ova). (In animals, the female mitotic sequence produces only one ovum; the other three haploid cells become "polar bodies".) In other organisms such as plants, the ...


2

There are many questions in your question. I'll try to answer each question pointwise. Which flags are used by the enzymes in the process of making the centromere to tell them that it is the right spot There are some centromere associated repeats in the DNA which mark the site for centromere assembly. There is no particular consensus sequence of this ...


2

The chance of having a child with Down's Syndrome does not only have to do with cell division, but the mechanism that allows spontaneous abortion to occur within the uterus of the mother. There is strong evidence for uterine selection against genetically disadvantaged embryos. However, as women approach the menopause and the risk of future infertility ...


2

The number of spindle fibres is actually more than total number of kinetochore pairs. The fibres attached to kinetochores are called K-fibres and the others are called polar fibres. I cant surely say that there is exactly one K-fibre per kinetochore but as per its definition and from the microscopic images you can conclude that there is one per kinetochore. ...


2

In an evolution mutations are often random and lead to differences in phenotype that can be adaptive under certain pressures. A lot of times mutation is a random process, but here are three cases I can think of off of the top of my head where I would say the organism is 'trying' to do it: HIV is a retrovirus, which means in its viral form its genome is ...


1

A recombinase only active during meiosis - Dmc1 and a general recombinase Rad51 coat the single-stranded DNA to form nucleoprotein filaments. These filaments hold the homologs together at the chiasma, the point of attachment during crossing over.


1

Couldn't fit in a comment... To me, your question sounds like "what are the possible advantages of sexual reproduction over asexual reproduction?" but in the meantime you're saying that you're not interested neither in the advantage of recombination nor in the advantage of "independent assortment". I don't quite see what you mean by "independent assortment" ...


1

In species where an individual can be haploid (for example in haplodiploidy) then cells produced by meiosis do multiply by mitosis in order for the individual to grow. From a brief scan the Wikipedia article on ploidy nicely summarises the various possibilities.


1

X chromosome has many important genes required for general housekeeping. So we need not really talk about X-chromosome genes. Here is a list of genes present on the X-chromosome. @Armatus, if all those genes were on autosomes then presence of Y wont be mandatory for male development. There are autosomal genes that are involved in sexual development for e.g. ...


1

There's a more meta-level discussion on meiosis, which is that there is an advantage for genes which can get themselves selected in meiosis more often would prosper. This is a prediction of the biologist Robert Trivers, working with Bill Hamilton in the late '60s, known also as the 'selfish gene'. In fact the reason the selfish gene theory was so ...


1

I think that Fair meiosis (I assume that you are referring to that chromosomes have an equal chance of transmission) can be seen as a byproduct of recombination at meiosis, which makes every chromosome a mosaic of maternal and paternal chromosomes. Therefore, selection does not act on chromosomes as a single unit, and "unfair" meiosis becomes meaningless. ...


1

During mitosis a diploid cell (2n = two copies of each chromosome, one from each parent) replicates its DNA so that it now has four copies of each chromosome. Then it divides, each daughter cell receives two copies of each chromosome and is again 2n. In meiosis a diploid cell (2n) replicates its DNA so that it now has four copies of each chromosome. Then ...


1

The answer is yes, not only meiotic, but any DNA double-strand breaks will be detected as long as they are processed by homologous recombination. This method (SSDS) is based on the detection of resected ssDNA ends at DSBs. The only difference for the mitotic breaks will be that you cannot use anti-DMC1 for ChIP. Instead, you should use either anti-Rad51 or ...


1

Meiosis, as you know, have two stages, Meiosis I and II. The oocyte is arrested during metaphase II of MEOISIS II. This arrest is facilitated by a complex called "Cytostatic Factor" (CSF). After fertilization, the sperm induces a rise in intracellular calcium ion which activates and enzyme, Calmodulin Kinase II. This complex, through a series of ...


1

Untill puberty the follicles grown from primordial to antral stage (secondary folliccle) and oocytes are arrested in diplotene of profase I of meiosis I, without polar body, with a nucleous called germinative vesicle. After puberty, with gonadotrophis, they can grow more and ovulate. With LH surge they are stimulated to continuing meiosis and they lose the ...


1

I seem to understand the thing now. The video is utterly simplified for animal cell meiosis I and II. In oogenesis, you get after every anaphase one cell with very little cytoplasm, polar body, and another cell with much cytoplasm. In the video, the amount of cytoplasm is equal so the thing is idealized. The video is better to explain male gametogenesis: ...



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