Mitosis&Meiosis An Answer Book 2015 PDF

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Dr. Connelly, Gen Bio I

Mitosis/Meiosis Questions and Answers Definitions: Chromosome – carries genes; located in the nucleus of eukaryotes Chromatin – are made of DNA and proteins; are used to make chromosomes

Chromatids - (a.k.a. “Sister Chromatids”) – identical copy of a single chromosome; offered shown as a “X” in diagrams; connected by a centromere; a “pair” of sister chromatids connected at the centromere would be considered a single chromosome; for counting purposes, we count all sister chromatids if we want the chromatid number, and the pairs if we want the chromosome number (see table later with all of the numbers for humans in the stages of mitosis and meiosis). Centromeres – a point on the chromosome that holds the sister chromatids together; the attachment point for spindle fibers during Anaphase in mitosis and meiosis is referred to as the kinetochore Centrosomes/Centrioles – produce the spindle fibers (microtubules) that are used to separate homologous chromosomes or sister chromatids during mitosis and meiosis; these are replicated during interphase. Homologous chromosomes – a pair of chromosomes that are the same size and length; they carry the same genes, but the genes that they carry may code for varying traits (i.e. one chromosome codes for brown hair and the other codes for blonde hair – they both code for hair color, so they are homologous); one set of homologous chromosomes is inherited from each parent; “pair of shoes”. These are NOT the same as sister chromatids. Sister chromatids - see Chromatids

Haploid (Haploid Cell) – a single complement of chromosomes (NOT homologous pairs); a cell containing “n” chromosomes – the “half number” of chromosomes in a somatic cell, or all chromosomes in a gamete; meiosis produces 4 genetically identical haploid cells (gametes); the number of chromosomes is reduced rom diploid to haploid in meiosis I (anaphase I); Humans haploid number = 23

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Dr. Connelly, Gen Bio I

Diploid (Diploid Cell) – the full set of homologous chromosomes in a somatic cell, including the set from Mom and the set from Dad; a cell containing “2n” chromosomes; Humans diploid number = 46 Gene – molecular unit of heredity; located on chromosomes; many genes per chromosome. More specific questions: What’s the difference between all of the C words? See Definitions I hate that chromosomes become chromatids that make up chromosomes which are homologous but can also be part of a homologous pair. Lameness. See Definitions Why are chromatids and chromosomes names so confusingly? See Definitions What is the difference between sister chromatids and non-sister chromatids? Ummm … there are no non-sister chromatids? What is the difference between sister chromatids and homologous chromsomes? See definitions. When is it sister chromatids or a chromosome or a homologous pair or just homologous? Sister chromatids refer to the replicated DNA state (after Interphase) at the beginning of mitosis or meiosis ONLY. A sister chromatid is an identical copy of a single chromosome. A chromatid would be a single one of these. But, we talk about pairs of sister chromatids (the “X” formation seen at the beginning of any cell division). Yes, this means that 2 of the sister chromatids are the same in each cell.

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Dr. Connelly, Gen Bio I

A homologous chromosome is a single chromosome, either from Mom or Dad. It CAN be in a replicated state (“X” formation). If it is referring to only one of them (Mom or Dad), then it is a homologous (one) chromosome, whether it is replicated or not. A pair of homologous chromosomes would refer to the chromosome pair from Mom and Dad at a specific chromosome number (i.e. Chromosome #11 – both chromosomes – one from Mom and one from Dad). These can also be in the replicated state. So, you would see two “X” formations side by side. When we count the number of sister chromatids, you count ALL of them in the replicated state. If we count homologous chromosomes, you count all of the chromosomes present (from Mom and Dad), but you ignore the sister chromatids IF they are in a replicated state.

What starts mitosis and meiosis? Chemical signaling. What is the biggest difference between mitosis and meiosis? Resulting cells (diploid vs. haploid, 2 vs. 4). What triggers the checkpoints of mitosis and interphase? Chemical signaling. Homeostasis must be maintained, and some of that is regulating the cell cycles. What happens with the doubled material is the cell does not pass the first test (Dr.C. says … check point??) to enter G2? Nothing. It sits there. If it is never allowed to continue it will eventually be broken down. Why do chromosomes form X shapes? Why not circles or lines or some other thing that can be ripped in half? You have two linear chromosomes jointed at a single common point. How are you going to make them a circle? Can the sister chromatids be called sister chromatids after recombination or crossover? After crossover they are not the same. Correct. But, the definition of sister chromatids is that they are identical copies (produced in Interphase) and held together at the centromere. You are being too literal about the “same” thing.

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Dr. Connelly, Gen Bio I

Which stage is active when the nuclear envelope disappears?

Prophase. The envelope has to be gone to start prometaphase, otherwise the spindle fibers could not always reach the kinetochores. What is the difference between Prophase (mitosis) and Prophase I (meiosis I)? There is no difference … other than crossing over is rare in mitotic prophase and common in prophase I of meiosis I. See comments on that difference later. What is the difference between Anaphase (mitosis) and Anaphase I (meiosis I)? Mitosis anaphase separates sister chromatids, Anaphase I (meiosis) separates homologous chromosomes. Technically there is no difference in the process between Mitosis Anaphase and Meiosis Anaphase II … both separate sister chromatids. In meiosis it just does it for half the number of chromosomes. How do sister chromatids separate?

They are pulled apart by the spindle fibers produced in the Centrosomes/ Centrioles attached to the kinetochore of the centromere. Is prometaphase important to know? Yes. But, focus on the spindle fibers attaching to the kinetochore of the centromere only for this stage. It’s an organizational stage of mitosis. It is not a part of meiosis. When do tetrads form? What does tetrad mean? During Prophase I of Meiosis I Tetrad – a pair of homologous chromosomes in their replicated state; seen as a two “X”’s in the formation at the beginning of Prophase I or Meiosis I What causes a tetrad to form during meiosis I, but not during mitosis? Tetrads do not (generally) form in mitosis because the homologous chromosomes are not signaled to pair up as they are in meiosis. It has been recently discovered that organisms that reproduce asexually may “force” crossing over during mitosis to increase their genetic variability. Interesting!

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Dr. Connelly, Gen Bio I

Crossing over occurs in prophase. Is that also part of prometaphase? Does prometaphase even occur in meiosis? Crossing over is complete before prometaphase beings. We do not even consider prometaphase in meiosis.

Why does 1 chromsome (“X”) = 2 chromosomes (\ + \)? Count the centrosomes to know how many chromosomes you have. “X” = sister chromatids replicated, or one chromosome (one centromere). “\” = chromosome and ‘”\” = chromosome .. both with 1 centromere, so 2 chromosomes (centromeres) total. When chromosomes duplicate and form an “X”, are they still called chromosomes? The “X” is a chromosome. The “legs” of the “X” are sister chromatids. When is cytokinesis complete? What is it? Not until interphase begins. Cytokinesis is the splitting of the cell in to two daughter cells. In meiosis it occurs twice (Cytokinesis I and Cytokinesis II) What are the steps of interphase? G1 = growth of newly divided cell S = replication of DNA G2 = increase in cytoplasm and duplication of organelles in preparation for cell division (mitosis OR meiosis) Are there any other sub-steps in mitosis steps? No.

What occurs or are the results of meiosis I? Two haploid daughter cells with sister chromatids still present.

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Dr. Connelly, Gen Bio I

What would happen if meiosis does not continue to meiosis II? You would have haploid cells, but they are still replicated. So, they would be nonfunctional as gametes (too What is “2n”? 2n refers to a cell being diploid. It has two versions of each chromosome (1 from mom and 1 from dad). Your somatic cells are diploid. Your only cells that are haploid (“n”) are your gametes. They only have one version of each chromosome due to division of the homologous chromosomes in Meiosis I. How many chromosomes at the end of mitosis? Ploidy? Each daughter cell of mitosis MUST be genetically identical to the parent. So, in humans, there will be 46 chromosomes, 23 homologous pairs, 0 sister chromatids. These are “2n” (diploid) cells. How many chromosomes at the end of meiosis? Ploidy? Meiosis produces 4 genetically different haploid cells from a single parent cell. These are “n” cells (haploid) Are there 23 chromosomes in every cell of your body? Yes … there are 23 chromosomes (haploid) in your gametes, but 23 PAIRS of homologous chromosomes in all your other cells (46 total chromosomes) When do you count the chromosome individually or a pair? What? You mean homologous pairs? Or do you mean sister chromatids counting as a single chromosome? See definitions. I know that meiosis creates 4 haploid cells, but are diploids produced at any stage? Meiosis begins with a diploid cell (called precursor cells). The cells at the end of meiosis 1 are haploid.

What do mean by what’s being separated? Anaphase. Sister chromatids or homologous chromsomes?

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Dr. Connelly, Gen Bio I

What’s the deal with meiosis II? What’s the difference between I and II? Meiosis II is like Mitosis. It’s purpose is to separate sister chromatids. The difference between Meiosis II and Mitosis is the number of chromosomes. In Mitosis, you are separating the sister chromatids of 46 chromosomes; in meiosis only 23. Meiosis I separated homologous chromosomes (in the replicated state) from one another. You are splitting the tetrad in half. So, at the end of meiosis I, you have 23 chromosomes (HAPLOID) in each cell, BUT they are still replicated (with their sister chromatids). You must complete Meiosis II to separate the sister chromatids.

Do 2 sister chromatids attached at the centromere make up one chromosome? Yes. Does interphase count as part of the mitotic cycle, or is it outside of the actual division process? Interphase is part of the cell cycle, but not part of mitosis. Main role in each step of mitosis Prophase – organize chromosomes; begin building spindle fibers; break down the nuclear envelope Prometaphase – organize chromosomes; spindle fibers attach to the kinetochore of the centromere Metaphase – align chromosomes on the Metaphase plate (in the middle) to prepare for Anaphase Anaphase – separate the sister chromatids (break the “X” formation) Telophase – Reform the nuclear envelopes around the two sets of chromosomes; begin the build the cell plate (in plants ONLY) or begin to “pinch in” the cell at the cleavage furrow (animal cells – plasma membrane folding in) Cytokinesis – finishing dividing the cell by separating the two new nuclei, splitting the cytoplasm and diving the organelles What happens to the cytoskeleton of the parent cell during these processes?

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Dr. Connelly, Gen Bio I

Some breaks down and reforms. Others will remain for structural support and will be “broken” by the process of splitting. When do we know if we are suppose to include prometaphse as phase? Prometaphase only in mitosis (not meiosis). Metaphase and prometaphase are very different. See steps above for review. What causes the organelles to move to the appropriate orientations during the replication process? Nothing other than chemicals and some cytoskeleton. We split the cell and hope for semi-equal division of the organelles. What is the main difference / location of chromosomes / sister chromatids in anaphase & telophase? Are they moving towards the poles in anaphase and in the poles at telophase? We consider anaphase to be the separation and movement to the poles, arriving at the poles at the end of anaphase / beginning of telophase. Telophase is identified by the forming of the nuclear envelopes. What is the longest phase in mitosis, excluding interphase? Well, since interphase is not part of mitosis, general consensus for an average is Prophase. In mitosis, 92 chromosomes in each daughter cell, right? NO! Identical cells are formed to the original. 46 chromosomes per cell in humans.

What is a good way to remember the order of steps in mitosis and meiosis and the differences? PMAT-C (“pee mat – see??”) for meiosis (twice) and PPMAT-C (“pee pee mat – see??”) for mitosis. The differences between the stages? P = plain to see (chromosomes) M = middle (chromosomes line of in the middle) A = apart (separating chromosomes / chromatids)

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Dr. Connelly, Gen Bio I

T = two nuclei C = cut cell Anaphase I, etc vs. Anaphase II. Is that in mitosis, or meiosis? Meiosis. We only go through the steps once in mitosis, so we don’t number them. Do plants go through meiosis? Yes. Where does meiosis occur? In the ovaries or testes for humans. Is polyploidy the same as diploid? Technically yes. Polyploidy would be any “ploidy” greater than 1. But, we reserve polyploidy to describe plants, since often they are 4n, 16n, 64n, etc. If you start with chromatids and duplicated to sister chromatids then split to have 1 of each chromatid in each cell, how do we have 46 chromosomes? Um. No. We start with 46 chromosomes, replicate to 92 sister chromatids, and split 92 in half, taking us back to 46 chromosomes. In mitosis. When in mitosis and meiosis do sister chromatids stop being sister chromatids and become chromosomes? As soon as they are no longer attached (anaphase). How do you know how many chromosomes/chromatids are formed from the parent cells? How many are you starting with? If you are doing mitosis, the chromosomes have to be equal in the parent and daughter cells. In meiosis the daughter cell will have half the number of chromosomes than the parent cell. See the table below to outline the chromosomes and chromatids at every step of mitosis and meiosis. Do we need to know about cancer cells?

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Dr. Connelly, Gen Bio I

Just know that cancer is uncontrolled cell division. If anything interferes with proper cell cycle and division, you can enter a cancer state. Do mitosis and meiosis happen in the same cells? No. See differences below.

Does meiosis happen in all living organisms? Only those that reproduce sexually. Is there an easy way to remember diploid, haploid, etc and the amount of chromosomes present at that time? See definitions for haploid and diploid. The amount of chromosomes will depends on the organism. In humans, all somatic cells are diploid (46 chromosomes). Human gametes are haploid, one half of the total chromosome number (23 chromosomes). How is DNA replication different in prokaryotes and eukaryotes? DNA replication in eukaryotes occurs during Interphase and is more complex. In prokaryotes, DNA is replicated very rapidly during binary fission (“cell division”). DNA replication in both requires the same resources: nucleotides, sugars, polymerases, enzymes, co-factors, etc. How do chromosomes replicate? Chromosomes are DNA. The DNA replicates in Interphase-S When does your DNA need to replicate? At birth? Everyday? Whenever the chemical signals of your body initiate a cell cycle. Main difference between mitosis and meiosis. How do cells know when to do which? Mitosis produces 2 genetically identical diploid daughter cells that are identical to the parent cell for growth, repair, and replacement in eukaryotes and for asexual reproduction in prokaryotes. Only in somatic cells. Meiosis produces 4 genetically different haploid cells, all of which are different from the parent, for the production of gametes in sexually reproducing organisms. Only in cells to form gametes. Never in somatic cells.

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Dr. Connelly, Gen Bio I

At what point in meiosis are chromosomes duplicated, and when do the cells divide without duplicating chromosomes first? Always replicate in S of Interphase. Meiosis II results in a cell division that was not directly preceded by a replication. Is cytokinesis part of telophase? Cytokinesis begins in Telophase, but does not complete until after Telophase ends. Can all cells participate in meiosis, but because its not needed for body cells the ability to participate is turned off? Hmm. I would say all cells want to participate in mitosis, and only special cells are signaled to go through meiosis. What is a centriole? Part of the centrosome. Produces microtubules (spindle fibers) to pull apart sister chromatids and/or homologous chromosomes during Anaphase Is this true? “Mitosis – homologous chromosomes line up next to each other in a line across the middle of the cell. Meiosis – homologous chromosomes pair up behind each other as it lines up in the cell” Hmm. No. Not quite. In Mitosis, homologous chromosomes line up on the center plate with the sister chromatids of each pointing toward opposite poles (46 in a line). In Meiosis I, the tetrads line up on the central plate, with one homologous chromosome of each facing the poles (23 in a line). In Meiosis II, the 23 homologous chromosomes in each cell line up on the central plate and the sister chromatids are pointing to opposite poles (23 in a line). What is a kinetochore? The joining point of the spindle fibers to the centromeres. What is allele? It is a variation in a chromosome. It refers to the homologous chromosomes (one from Mom and one from Dad). The alleles are the variations in the same gene that your parents gave to you. See the definitions of homologous chromosomes for more. Is one homologous chromosome pair considered one chromosome?

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Dr. Connelly, Gen Bio I

No. See definitions of homologous pairs and homologous chromosomes above. How are pairs of chromosomes matched in mitosis? They aren’t. Do regular cells have haploid numbers? Sure. Somatic cells are diploid (2n) in humans (46 chromosomes), but we also say that they have 23 pairs of homologous chromosomes, which is their haploid (“n”) number. What happens to the centrosomes/spindle fibers between meiosis I and Meiosis II? Do the disassemble and the reassemble again in Prophase II? Do the cenrosomes double twice? When do the centrosomes replicate a second time for the second split in meiosis? Remember, we are halving the number of chromosomes at the end of Meiosis I, so we only need half as many centrosomes. The Centrosomes are maintained between Meiosis I and Meiosis II (remember, they are replicated in Interphase – no Interphase between Meiosis I and Meiosis II). The spindle fibers will break down, at least partially, and rebuild beginning in Prophase II. What is the difference between plant and animal mitosis? The only difference is Cytokinesis. In Animals, the cleavage furrow forms to “pinch” the cell in to two new cells. In Plants, the plasma membrane will separate in the cleavage furrow manner, like Animals, but in addition the plant cell must rebuild the cell wall, using cell plates (beginning in the middle of the cell and building outward). What is the difference between plant and animal meiosis? Plants do not produce eggs and sperm, per say. They produce other forms of gametes. But, oth...