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Questions tagged [meiosis]

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

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My understanding of chromosomes and the processes related to them is lacking [closed]

I'm sorry for the incredibly simple question, I just can't seem to find any answers elsewhere online. I am a high school student currently studying for the upcoming AP biology exam, and recently I ...
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1answer
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Possible combinations in the Meiosis' Telophase 1

As you might already know Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of chromosomes in a cell before reproduction $^{[1]}$ One of the reasons why ...
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Does the law of independent assortment apply to homologous chromosomes or alleles, or both?

My textbook is giving me two definitions 1st def: "random orientation of homologous chromosomes at the metaphase plate in meiosis 1." 2nd def: "alleles for one gene separate into gametes ...
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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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Why sperms don't forms follicles

As all of us know that in meiosis oocyte forms follicles and egg cells, so my question is that if an oocyte can form follicles then why sperm cells do not forms the follicles? And in evolutionary ...
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1answer
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Fertilization of the human egg- where does our centrosome come from?

Is there a centrosome in a human egg cell? Is the reason why the egg cell remains paused before meiosis 2 because there isn't a centrosome, and it only divides when the sperm fertilizes it thus it can ...
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68 views

When in the cell cycle is the number of chromosomes normally reduced?

Page 96 of the Study Guide for Campbell Biology, 11th Edition has the following question: A reduction in the number of chromosomes per cell occurs a. During meiosis I b. During meiosis ...
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Which is the correct term haploid daughter cells or haploid parent cells?

Meiosis 2 begins with 2 haploid parent cells and ends with 4 haploid daughter cells (gametes). Gametes from the opposite sex can now merge together and fertilize. If I were to refer to a specific ...
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1answer
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Do chromosomes line up as pairs in mitosis or meiosis?

Here is a question from the book SAT II Success Biology E/M (where the SAT is the exam taken by the American high school students): Homologous chromosomes line up in pairs in (A) metaphase of ...
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What confuses me about “homologous gene”

When I first encountered homologous genes I thought those genes are identical because the text book said so, and "homologous" meant the same knowledge. But as I studied along, it comes out that ...
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1answer
110 views

During what phase is the cell polyploid? [closed]

During what phase is the cell polyploid? Why is it polyploid at this point--what has happened to create this state and why is it important to the process?
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1answer
511 views

How long does each of the stages in meiosis take?

For each stages of meiosis (i.e. Interphase, Prophase I, ...), I wanted to know the time between each stages either in percentages or minutes. However, while I could find the cell cycle for mitosis ...
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1answer
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What exactly happens during the crossover [closed]

My knowledge of biology is rather limited, but I think I have a grasp of some basic concepts. For me (as a person close to math) a chromosome is a sequence of elements from the set {A,C,T,G} of some (...
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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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What does the nucleus look like in S phase of Meiosis?

I was watching an animation video about Meiosis and this is what the video shows (pics attached.) It shows that before synthesis, each chromosome exists as single chromatid and then after replication,...
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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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DNA replication during Mitosis

I am a bit confused. During Meiosis, DNA is replicated to form a cell with half the DNA and likely to have variations. But since the replication process of meiosis and mitosis are the same, why do DNA ...
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1answer
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How would homologous recombination and mutations affect speciation?

I'm wondering how homologous recombination and mutations can affect how speciation can occur from one species (so that 2 will be created). I'm doing research and I found that different mutations and ...
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How do biologists determine the parents of a child

I am not well-versed in biology so this question might be wrong. As far as I understand meiosis, two germ line cells with 23 chromosomes each (one cell from the father and another from the mother) ...
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1answer
240 views

Can you use a cell in meiosis to create a karyotype?

Why might it be problematic to use a cell undergoing meiosis to create a karyotype?
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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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Why does cell waste energy in meiosis, between meiosis 1&2

As far as I have learnt about meiosis I have read that anaphase 1 is followed by telophase 2 where chromosomes change back to reticulum.but in the very next stage i.e prophase 2 they again start ...
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292 views

Does crossover happen between chromosomes from grandparents?

Rephrasing question: does crossover happen after sperm and egg meet each other, but before formed fetus starts to grow? As I understand sperm and egg of human are haploid cells. That means this cells ...
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1answer
510 views

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 ...
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1answer
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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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How does the spindle fiber find the kinetochore?

I am curious if anyone knows the exact mechanism of how exactly does the spindle fiber find the kinetochore? it certainly seems like a fairly non-spontaneous reaction for a spindle fiber to reach all ...
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1answer
787 views

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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Recombination frequencies

I have been learning about recombination frequencies, but an still getting a bit confused despite having gone over many of the links in Google regarding them. I was wondering if someone could verify ...
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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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If you start with 1 cell how many are at the end of meiosis? [closed]

If you start with 1 cell how many are at the end of meiosis? Can someone help me understand the process of what happens to the cells in the process of meiosis I and II
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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 ...
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1answer
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Where did the nondisjunction occur?

A father with gene AC has a child with gene ACC. Where did the nondisjunction occur? (Meiosis I, Meiosis II, none of the above) I do not know because both Meiosis I and II have the possibility of ...
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1answer
310 views

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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what chromatin factors are the most potent supressors of meiotic crossover?

I think linker histone H1 is probably involved, but the literature is scant. What else prevents crossovers from becoming hyper-frequent during meiosis?
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How does chromosome number get halved in meiosis I?

In meiosis 1, it is said that chromosome numbers become halved in the two daughter cells. For example, in a 2n human cell there are 46 chromosomes. During meiosis 1, the cell will undergo interphase ...
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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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684 views

Sister chromatids during meiosis

Sister chromatids $A)$ Cross over during prophase I of meiosis $B)$ separate during the first mitotic division $C)$ are produced during $S$ phase between cell divisions $D)$ cross ...
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Is this how female and male gametes look like in plants?

In the red box, the pink one is female sex cell I presume and the blue one is a male sex cell. http://prntscr.com/dsii2x Am I right? or are these chromosomes.. I'm confused. This is law of ...
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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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Why isn't meiosis II called mitosis (as the chromosome number doesn't half)?

Meiosis: a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores. Mitosis: a type ...
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955 views

Why do some organelle (like ER and Golgi complex) cannot be seen under microscope during cell division?

I have recently read in a book that organelles like ER (endoplasmic reticulum) and Golgi Complex cannot be seen under a compound microscope during cell division. Why does this happen, and where do the ...
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1answer
721 views

How can I determine where meiosis occurs in the life cycle of a plant?

To fill out this diagram with the mitosis, meiosis, and ploidy , we start with the definition that spores are haploid (N). Based on knowing that as the sperm and eggs are N, the gametophyte is also ...
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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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1answer
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Can life occur from a fertilised egg cell, in which both the egg and sperm possess an extra copy of a chromosome?

Patau, Edward, and Down Syndrome are all the result of either the egg or sperm cell possessing an extra copy of chromosome 13, 18, and 21, respectively. However, what would be the outcome if both ...
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Do Gametes contain mitochondria/chloroplasts from their parent cell?

It has now been established (according to the Cambridge A level text book) that organisms form a symbiotic partnership, typically by one engulfing the other – a process known as endosymbiosis. ...
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782 views

Does chromosome cross occur over male and female or vice versa? [closed]

My understanding is homologous chromosome pair, which means male and female chromosome inside the DNA. So if that's homologous how does male do with female? Does it flip over and change direction, ...
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2answers
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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, ...
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2answers
4k views

Can a non-disjunction event occur in meiosis II (in the paternal gametes) to result in an XXY male?

My professor stated that non-disjunction in meiosis II of the father cannot produce an XXY male. However, a disjunction event in meiosis II of the mother can. I'm not understanding why this is (?)
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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 ...
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Is there interphase between meiosis I and meiosis II?

Is there interphase between meiosis I and meiosis II? After 2 haploid cells are formed in meiosis I, do the cells go through a period of interphase (G1, S, G2) or do they go directly to meiosis II?