BIOEXCEL 190 - Mitosis & Meiosis KEY

Mitosis & Meiosis

____.) How do prokaryotes reproduce asexually?
binary fission

____.) In prokaryotes, what copies first, the chromosme or the rest of the cell?
the chromosome

____.) What two processes are involved in the cell cycle of eukaryotic cell division?
interphase and mitotic phase

a. The first event in which growth and DNA replication occur has three phases. What are they?
G1, S, G2
b. During which of these does DNA actually replicate itself?
S phase

____.) M phase of the cell cycle can be itself divided into four phases. What are they in the order that they occur?
Prophase, Metaphase, Anaphase, Telophase

a. In humans, what is the diploid number of somatic cells and what does this number represent?
2N = 46, number of chromosomes in a somatic cell
b. In humans, what is the haploid number of the gametes?
N = 23

____.) In the terms n and 2n, what does n represent?
the number of chromosomes in a gamete

____.) Put all of the following terms in their correct places on the diagram of the cell cycle below. Interphase, Mitotic Phase, S Phase, G1 Phase, G2 Phase, Cytokinesis, Metaphase, Prophase, Telophase, Anaphase

____.) Answer the following questions concerning human somatic cells:
a. A cellís total collection of DNA is called its ________genome_________ .
b. What are the hereditary units that are contained within the DNA molecules? ________genes_________
c. What is the predominant morphological form of the genome during the cell cycle? _________chromatin________
d. What DNA-protein complexes become visible with a light microscope during cell division? ________chromosomes_________
e. After replication, each chromosome consists of two ________sister chromatids_________ that are held together by a ________centromere_________ .
f. What are the specialized regions of the centromeres that attach to the spindle microtubules just before metaphase? ________kinetochores_________
g. An X-shaped region called a _______chiasmata__________ represents a crossing of nonsister chromatids, which are chromatids belonging to separate but homologous chromosomes.
h. What are the structures found in pairs in a dividing cell, each made up of nine sets of triplet microtubules, which help organize microtubule assembly? _________centrioles________
i. One of each of these is inherited from each parent. These posses genes for the same traits at corresponding loci. _______homologous chromosomes__________

____.) Using the following choices as phases of the cell cycle, choose the one that best fits the events below occurring at that phase.

a. the nucleoli disappear = Prophase
b. the nucleus is well-defined and bounded by a nuclear envelope = Interphase
c. the chromosomes convene on a plane in the middle of the two poles = Metaphase
d. the mitotic spindle forms = Prophase
e. a cleavage furrow begins to form = Telophase
f. the paired centromeres of each chromosome divide = Anaphase
g. the centromeres of all chrmosomes are in one line = Metaphase
h. the kinetochore forms = Prophase
i. genomic material is in the form of chromatin = Interphase
j. spindle apparatus begins moving sister chromatids to opposite poles = Anaphase
k. the nuclear envelope begins to form = Telophase
l. chromatin fiber becomes coiled into discrete chromosomes = Prophase

____.) Label the following pictures with their corresponding stage of mitosis. What is the ploidy at each of these stages?

____.) If a cell has half as much DNA as other cells in a mitotically active tissue, what phase would that cell be in? (G1, S, G2. M)

____.) In normal eukaryotic cells, mitosis will not begin until the entire genome is replicated. If this inhibition is removed so that mitosis begins during the S phase, what would be the consequences?
The genome would be incomplete because it hasn't completely replicated. Because of this, daughter cells won't receive the full genome and will most likely be inviable.

____.) How many chromosomes are in a human cell that has completed interphase? How many chromatids?
46 chromosomes, 92 chromatids

____.) Name the two stages involved in meiosis. How many daughter cells result in the meiotic divisions? How do the number of chromosomes in these daughter cell compare to those of the parents?
Meiosis I and Meiosis II, 4 daughter cells, each contain half the number of chromosomes as the parents

____.) Is meiosis preceded by the replication of chromosomes similar to mitosis? Why or why not?
Yes, to allow for an increase in genetic material that will later be distributed among four haploid daughter cells

____.) There is an S phase of DNA replication prior to Prophase of Mitosis and Prophase I of Meiosis. Why does this not also occur before Prophase II of Meiosis?
must maintain haploid number of chromosomes in daughter cells

____.) List the phase of Meiosis that corresponds to the descriptions below:
a. homologous chrmosomes (each with with two chromatids) pair up = Prophase I
b. sister chromatids line up on the plate equidistant between the two poles = Metaphase II
c. sister chromatids along with their centromeres move to the same pole = Anaphase I
d. each chromosome is replicated immediately before this phase = Prophase I
e. cytokinesis occurs to produce 4 daughter cells = Telophase II
f. tetrad can be seen with a light microscope (two answers!) = Prophase I, Metaphase I
g. two cells begin to form, each with a haploid number of chromosomes = Telophase I
h.homologous pairs line up on an equidistant plate = Metaphase I
i. a spindle apparatus appears a second time = Prophase II
j. a chiasmata can be seen (two answers!) = Prophase I, Metaphase I
k. individual chromatids move to opposite poles = Anaphase II

____.) The following picture represents the divisions of a spermatagonium to 4 daughter cells. Label the picture with the following terms indicating where it is each step occurs: Meiosis I, Meiosis II, S Phase. Also label each step as being n or 2n.

____.) If the DNA content of a diploid cell at G1 is X, then what would be the DNA content of the same cell during Metaphase I? What about Metaphase II? What is the ploidy of the cell during Metaphase I and Metaphase II?
X, 0.5X, 2N, N.

____.) When homologous chromosomes separate, do all paternal and maternal chromosomes stay together in the daughter cells? Explain.
Provide your own answer.

____.) Are the sister chromatids that separate during meiotic Anaphase II identical in their genetic sequence? Explain.
No, refer to the appropriate pages in the textbook.

____.) If cells are blocked in meiotic Metaphase II, prevented from moving on in meiosis, which one of the following will be prevented? B
a. Separation of homologous chromosomes
b. Separation of sister chromatids
c. Breakdown of the nuclear envelope
d. Formation of a tetrad

a. What are three major sources of genetric variation?
Refer to the appropriate pages in the textbook.
b. Explain what happens during each of these events.
Refer to the appropriate pages in the textbook.
c. During which specific phase of Meiosis does crossing over occur?
Prophase I

____.) Does crossing over change the number of genes on a chromosome? Explain.
If done correctly, no - there should be a one-to-one swap of DNA btween homologous chromosomes.

____.) Does crossing over create combinations of alleles on chromosomes that are not found in the parent? Explain.
Yes, each chromosome may now have a different allele of a particular gene that was not present on the parental chromosome previously.

____.) Regarding independent assortment, at what phase during meiosis are different traits of genes separated?
Meiosis I

____.) Sometimes during Meiosis I homologous chromosomesfail to separate and sometimes during Meiosis II, sister chromatids fail to separate. What is this failure to separate called?

____.) A normal gamete contains the haploid number of chromosomes. If two homologous chromosomes fail to separate during Meiosis I, what will be the number of chromosomes in the resulting gametes?
2 cells will have no chromosomes while the other 2 cells wil each have a diploid number of chromosomes.

____.) What disorder results from a nondisjunction event in which the resulting cell has 3 copies of chromosome 21?
Down Syndrome

____.) In an individual with Down Syndrome, could the defects be a result of an absence of genetic information? Why or why not?
No - no information is missing, there is just a 3rd copy of chromosome 21

____.) Nondisjunction can also occur with sex chromosomes. Name two disorders exhibiting this phenomenon and also list their genotypic descriptions.
Turner Syndrome (a single X sex chromosome) and Kleinfelters Syndrome (XXY)

____.) Fill in the following table regarding differences between mitosis and meiosis for a cell that has a diploid number of 8.

____.) What stage of Meiosis, I or II, most closely resembles Mitosis?

____.) What phases in mitosis and meiosis do sister chromatids separate?
Anaphase of Mitosis and Anaphase II of Meiosis

____.) Which of the following occur in meiosis but NOT in mitosis? B
I. Separation of sister chromatids on microtubules
II. Pairing of homologous chromosomes
III. Crossing over between sister chromatids

a. I only
b. II only
c. I and II
d. II and III

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