Questions tagged [meiosis]

Division of a diploid cell to produce four haploid cells for the purposes of reproduction.

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Why doesn't recombination occur in male Drosophila?

"Males do not show meiotic recombination, facilitating genetic studies." For a while I have known that this phenomenon occurs, this quote comes from the Wikipedia page on Drosophila melanogaster, and ...
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How does the molecular machinery choose where to cut a chromosome for recombination?

I'm wondering about a few technicalities of crossover in meiosis. The point of crossover is to create new chromosomes that don't have the same allele combinations as the original two chromosomes. ...
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Why does the chance of having a baby with Down's syndrome increase with the age of the mother?

Down's syndrome occurs when either the egg or the sperm cell contain on extra chromosome 21. To my understanding, women are born with all the egg cells in place already, so there's no further cell ...
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Does Human Female Meiosis II occur after fertilization with sperm?

I am reading the answer and I am getting confused by the sentence: At the end of meiosis I females have two daughter cells and meiosis II only occurs if and when fertilization occurs by a sperm ...
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protocol for pulldown of DNA breakpoints?

Is there any method to do pulldown enrichment of DNA breakpoints from a cell? I have found this paper reporting a method to enrich for the DNA single-strand breakpoints from meiotic recombination ...
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How is centriole number maintained during meiosis?

I've found a website (Pearson's BioCoach) that claims centrioles duplicate in Prophase II. Is this accurate? Does it depend on the species in question? Looking at three textbook illustrations of ...
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Do the eggs for larger litters come from the same meiosis events, or different ones?

There are some species of animals that give birth to more than one pup at a time. In these species, are the fertilized eggs all from one or a limited group of meiosis processes, or are they from ...
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Polyploidy, or why plants of different species can produce fertile offspring hybrids more frequently than animals?

This site says: Plants hybridize much more frequently and successfully than animals do. [...] Chromosomal doubling (polyploidy) occurs more frequently in plants and facilitates the fertility of the ...
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What type of cell do you start with in Meiosis?

Okay, I was learning about mitosis and meiosis in school and had a question. I know in Mitosis you first start off with a Diploid (2N) cell and then end up with two ...
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How do I identify the different stages of meiosis under microscope?

This is a question I'm troubled with as my exams are knocking at the door. I need help so I decided to post this here. Here's what I know and understand about meiotic stages: Specimen: Grasshopper (...
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What is the point of Meiosis II, considering Meiosis I already produced haploid cells?

Meiosis I is required so that the 2N cells become 1N, and so a 1N sperm and 1N egg can fuse to become 2N again. But why is meiosis II required? Why does our body need to go from 2 1N cells to 4 1N ...
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What is the main general difference between Mitosis and Meiosis?

I found such a clause: The general principle is that mitosis creates somatic cells and meiosis creates germ cells. However, I cannot agree. Each gametogonium needs to go through mitosis before ...
Léo Léopold Hertz 준영's user avatar
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When are a female's eggs created?

Since a human woman is born with a set number of eggs, and meiosis is the process by which sex cells are produced, would meiosis in a woman happen before she is born or soon after she was born? If ...
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Number of spindle fibres during Metaphase?

During metaphase, the chromosomes are arranged on the equatorial plate and are attached to spindle fibres. After S phase, can the cell be said to attain the configuration of 4n? Also, during ...
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What are centromeres *really*?

I've gathered that a centromere is a a region* where the DNA is bundles up even tighter (around protein different to Histone) and chromatids are 'joined'. However I'm still mostly in the dark ...
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No. of meiotic divisions to produce specific no. of seeds

If I want to produce 100 seeds. Then the no. of meiotic divisions is 125 which can be calculated by the formula x + x / 4. x = no. of seeds produced. How is this formula derived?
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Mitosis versus Meiosis I: What's the difference?

At the end of mitosis, one cell has divided into two diploid cells. But at the end of meiosis I, there are two haploid cells. How are the two processes different to produce these two types of cells?
John Smith's user avatar
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Randomness in living systems

The point of my question is not to talk about events that are uncontrolled by living organisms. My question is about controlled randomness, or I'd like to say adaptive random process. Process that are ...
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Aneuploidy in meiosis

I am quite confused about nondisjuction in anaphase II. If the double chromosome is not segregated, isn't it double. On pictures they are drawn as single but I don't understand why, and if they are ...
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How do nuclear membranes form during Telophase of Mitosis/Meiosis?

During Telophase, homologous chromosome pairs reach the poles of the cell with the help of microtubules. From there, nuclear membranes form around each new set of chromosomes. My confusion originates ...
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Meiosis vs. Mitosis

Meiosis is a type of cell division that reduces the chromosome number from 2n to n to make gametes viable for reproduction in humans. I know that during meiosis, there is independent assortment and ...
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Are there verbs for "undergo mitosis" and "undergo meiosis"?

From my experience on SE sites, I believe this is the right site to ask this question under "terminology". I've been trying to find out whether English has one-word verbs for "undergo mitosis" and "...
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How is it possible for monosomies to occur?

I was taught in biology class that a cell dies if it doesn't have at least one copy of a chromosome "type". If this is the case, that means that: Zygotes without a copy of a specific chromosome (for ...
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Why did Fair Meiosis evolve?

How and why did Fair Meiosis evolve? I can hardly think that it provided a fitness advantage to the individual carrying the mutation. Why would it? Or did it evolve through lineage selection? Or was ...
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Germ cells vs. gametes

Naively, I thought that germ cells are diploid (in diploid species like human/mouse at least). Then, germ cells undergo meiosis and become haploid. I thought this was the critical change that defined ...
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Formula for number of divisions required to form x number of cells (Mitosis and Meiosis)

In case of Mitotic Division, we say that if the total number of cells formed by mitotic divisions are $x$, then counting from the first cell onwards, we get $x-1$ divisions ($N$) $N = x-1$ This is ...
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What's the distinction between a tetrad and a synaptonemal complex in meiosis?

What's the distinction between a tetrad and a synaptonemal complex in meiosis? Are they synonyms? I ask because the concepts seem very closely related, but it seems like there may be a subtle ...
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What makes protein binding to the DNA random?

We know that the genetic recombination process in known as a random process. On the other hand, it has also been discovered that certain proteins (such as PRDM9) determine what recombination hotspots ...
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What is the purpose of two cell divisions in meiosis?

At the moment, my thoughts are that the two cell divisions are necessary for recombination to occur, although I am not sure. I cannot really see why technically, the chromosome from each parent cannot ...
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Why there is replication of DNA before meiosis?

It seems to me that, even without replication of DNA before meiosis, the homologous pairs can still do crossover, and then be pulled to opposite poles, directly forming 2 haploid gametes.
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Division of Polar Body

The first polar body formed after meiosis-I is completed in oocyte, may or may not divide. Why is the statement that "it may or may not divide"? Is it random ?
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Coiling of chromatids during cell division [closed]

What is exactly coiling of chromosomes? I just heard about the names i.e paranemic, plectonemic, orthostichious, anorthospiral. I have ecaxtly no idea of what phenomenon is this. Also what type of ...
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How do gene locations change during crossing over events?

Suppose you have two variants from the same species, which have slightly different chromosomes I's to each other. Genes may be in slightly different positions on the chromosome, and the lengths of the ...
Jabbath's user avatar
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Could multiplexed CRISPR disable the mitotic and meiotic genes of cancerous cells?

Although I believe there is a good reason -- or reasons -- why this theory, that CRISPR could disable the genes for division in cancerous cells, is incorrect, I haven't been able to find them. In ...
Colin Pace's user avatar
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Human ancestor reproduction after chromosome fusion

I read somewhere that human chromosome 2 is the result of 2 primate chromosomes fusing together somewhere along our evolutionary journey. This is why we have 23 chromosomes while other primates have ...
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Doesn't meiosis form two pairs of similar cells and two pairs of opposite cells?

I am learning about meiosis in biology. I've learnt that the crossing-over in metaphase I only exchanges small portions of DNA at the tips of the chromosomes. Doesn't this mean that: After meiosis I, ...
a8848's user avatar
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Mechanics of Chromosomal Crossover

When chromosomal crossover occurs, two matched chromosomes swap matched sections of their chromosomes. My question is: how does the cell select where to to make the break on both chromosomes? Is it ...
Sean Lake's user avatar
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tetrads in meiosis are held together by what

This is from SAT subject biology test practice question. The answer it gave me was both chiasmata and centromeres. I can understand they are held by chiasmata but why also centromeres? I looked it up, ...
user40003's user avatar
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Why does crossing over take place at all?

I already know that crossing over causes genetic variation. My question is that since DNA is a stable molecule, why would it undergo process like crossing over during which it becomes so unstable and ...
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Interpreting graph of mitosis and meiosis

Note : Consider the y axis as 1,2,3,4(not 2,3,4) and x axis as time. Roman numerals should be considered from I-X ( some are not correct here ) Which stages show mitosis? My answer : III-V Which ...
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How do you see the stage of the second meiotic arrest in oogenesis in the given video?

My old question raised this new question. After reading this page I can say now that metaphase is the stage in which the second meiotic arrest occurs within oogenesis: The oocyte is arrested again ...
Léo Léopold Hertz 준영's user avatar
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1 answer
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Cell organels during cell reproduction

When one studies cell division, usually the process is explained through what happens with the DNA of the cell, particularly, that in eukaryotes the nucleus dissolves. But what happens to the rest of ...
Ana Galois's user avatar
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Question about genetic recombination

I am having some difficulty understanding a few things about genetic recombination, in part because of confusion from different diagrams in books. First of all, I wanted to verify whether I have ...
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What has to duplicate before cell enters M phase? [closed]

What has to duplicate before cell enters M phase? DNA histones centrosome mitochondria (any other organelles?) condensins (not sure?) have I forgotten anything? Thank you in advance!
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Distinguishing between mitotic metaphase and metaphase II of meiosis

I'm sorry if this seems like a silly question, but I was brushing up on some cell cycle dynamics and realized that everyone was talking about the differences between metaphase I and II, and since ...
Slater Victoroff's user avatar
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0 answers
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Is there a gene that starts meiosis 2? [closed]

Yesterday I thought about a question and asked it to my friend. The question was which gene is completely the same for a male cell that made meiosis 1 recently. My answer was the gene that starts ...
burak's user avatar
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2 votes
2 answers
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How are germ cells not reduced in number?

If germ cells produce haploid daughter cells by meiosis and are thereby "consumed" (where there was a germ cell there are then 4 daughter cells), where do the germ cells come from? I asked my biology ...
Graham's user avatar
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1 answer
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Considering Two Genes, Are There Only Two Possible Outcomes for the Four Gametes Produced After Meiosis, Regardless of Independent Assortment?

Is it true that for a single meiotic event when considering only two genes, there are only two possible genetic outcomes among the four gametes produced, regardless of whether the two genes are found ...
Growing6884's user avatar
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2 answers
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Do the four cells produced by meiosis each divide into four cells again?

In the beginning of meiosis, there is one cell. During meiosis, 1 cell divides into 4 cells. Does each of these 4 cells divide each into 4 more cells?
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Is there random assortment in metaphase II?

First, a little notation. Call a the first chromosome from my mother and A its homologous partner from my father. ...
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