The Cell Cycle
How many centromeres are there in each tetrad?
-2
After cytokinesis of meiosis I is complete, how many chromosomes are present?
-23
Each has how many chromosomes?
-23
How many tetrads are there at the zygotene phase?
-23
After the completion of cytokinesis II, how many haploid cells have been produced?
-4
How many chromosomes exist during anaphase II?
-46
Throughout prophase I, how many chromosomes are found in the cell?
-46
How many chromosomes exist during the zygotene phase?
-46 (due to the fact that there are 46 centromeres)
What occurs during the synthetic phase?
-46 strands of chromatin are replicated
How many chromosomes exist during anaphase?
-92
Throughout prophase I, how many chromatids are found in the cell?
-92
At what phase is each cell arrested?
-G1
If a cell is never destined to divide again, in what phase will it remain arrested in?
-G1 (first growth phase)
What three phases can interphase be divided into?
-G1 (first growth phase) -S (synthetic phase) -G2 (second growth phase)
What occurs during G1?
-RNA and proteins are being synthesized -centriole pair separates -cell and nucleus begin to increase in volume
What is this pair referred to as?
-a dyad
Since there is a reduction in the number of chromosomes, what is this division referred to as?
-a reductive division
As such, a homologous chromosome pair is also referred to as...?
-a tetrad
For each bivalent/tetrad, on average how many cross-over events occur?
-about 10
What occurs in telophase?
-all daughter chromosomes have reached their respective poles -chromosomes begin to uncoil and extend -microtubules begin to disappear -nuclear membrane forms around the two daughter nuclei -nucleolus reappears -cleavage furrow deepens
What are alleles?
-alternate forms of the same gene
Where do the events of crossing-over become visible?
-at structures called chiasmata
What are the homologous chromosomes which have undergone synapsis referred to as?
-bivalent
How can you easily identify the ploidy number (n) within a cell?
-by counting the number of centromeres
How can you easily identify the amount of total DNA within a cell (c)?
-by counting the number of chromatids
WHat occurs during anaphase II?
-chromatids are pulled to the opposite poles of the dividing cell
What occurs during G2?
-chromatin begins to condense and become more tightly coiled -protein synthesis is quite active
After the chromatin are replicated, what is the chromosome number?
-chromosome number remains 46
What occurs during metaphase?
-chromosomes align themselves along the metaphase plate
What occurs during leptotene?
-chromosomes become visible
What occurs during prophase II?
-chromosomes begin to condense -microtubules of the spindle apparatus attach to the kinetochores of each chromosome
What occurs during metaphase II?
-chromosomes line up along the metaphase plate
What is telophase usually followed by?
-cytokinesis
What occurs during cytokinesis?
-cytoplasm is divided
At what stage are developing oocytes arrested until the onset of puberty?
-diplotene of prophase I
How many chromatids are contained within a bivalent?
-four
What occurs during the pachytene phase?
-genetic recombination occurs through a process known as crossing over
As such, the cells are considered to be diploid or haploid?
-haploid
What occurs during metaphase I?
-homologous chromosomes align along the metaphase plate
What occurs during zygotene?
-homologous chromosomes begin to pair up longitudinally -synaptonemal complex forms
What occurs during the diplotene phase?
-homologous chromosomes beging to separate
When does cytokinesis usually occur?
-in late anaphase
What are the three major stages of the cell cycle?
-interphase -mitosis -cytokinesis
What are the five states of prophase I?
-leptotene -zygotene -pachytene -diplotene -diakinesis
What process is used to produce germ cells?
-meiosis
What occurs during anaphase I?
-microtubules pull the homologous chromosomes apart -chromosomes migrate towards the poles
What occurs during telophase I?
-migrating chromosomes complete their movement to opposite poles -nuclear membrane reforms
What process is used to produce somatic cells?
-mitosis
Does DNA replication take place during S phase of interphase II?
-no
What occurs during diakinesis?
-nuclear envelope begins to break down -nucleoli disappear -homologous chromosomes begin to separate
What occurs during telophase II?
-nuclear membrane forms around the decondensing chromosomes -cleavage furrow deepens
In the female, what are gametes called?
-ova
At what stage of mitosis can you first see chromosomes?
-prophase
What is each chromosome that migrates toward a pole composed of?
-sister chromatids
What occurs during anaphase?
-sister chromatids move towards opposite poles
What is the synaptonemal complex?
-specialized protein and RNA scaffold that appears between the pairing chromosomes
In the male, what are gametes called?
-spermatozoa
What occurs in cytokinesis?
-the cytoplasmic division of a cell into two daughter cells
What occurs during prophase?
-two centriole pairs begin to move apart -microtubules radiate from each centriole pair -condensation of chromosomes is complete -chromosomes become visible -nucleolus disappears -nuclear membrane breaks down
What are the four phases of mitosis?
1. prophase 2. metaphase 3. anaphase 4. telophase
After cytokinesis II?
1C
After anaphase I?
2C
After anaphase II?
2C
After cytokinesis?
2C
After telophase II?
2C
During metaphase II?
2C
During prophase II?
2C
How much DNA is in a single set of chromosomes in G1 prior to mitosis?
2C
Anaphase II?
2N
Telophase II?
2N
At anaphase I?
2n
At metaphase I?
2n
At telophase I?
2n
Ploidy number at anaphase?
2n
Ploidy number at metaphase?
2n
Ploidy number at prophase I of meosis?
2n
Ploidy number following cytokinesis?
2n
What is the ploidy number at prophase of mitosis?
2n
After S phase?
4C
After anaphase?
4C
During metaphase I?
4C
How much DNA is present during prophase I of meiosis?
4C
In metaphase?
4C
In prophase?
4C
Ploidy number at telophase?
4n
At prophase II?
N
Following cytokinesis II?
N
Metaphase II?
N
At meiotic interphase I?
N!!!
