Chapter 2 - HW 3
When cells withdraw from the continuous cell cycle and enter a "quiescent" phase, they are said to be in what stage?
G0
From which phase of the cell cycle does a cell enter G0 phase?
G1
Events that occur during mitosis
- Microtubules assemble between centrioles - Nuclear membrane breaks down - Chromosomes condense
Which list of steps in the eukaryotic cell is given in the correct order? (step order listed left to right)
...G1 - S - G2 - M - G1... ** The S phase is both preceded and followed by a period of growth (G1 and G2, respectively). After the M phase, the cell re-enters the G1 phase **
If a typical somatic cell has 64 chromosomes, how many chromosomes are expected in each gamete of that organism?
32
Meiosis involves
2 sequential cellular divisions
How many chromosomes are present in the second polar body?
5
How many chromosomes are present in the mature ovum?
7
How many first polar bodies would be formed?
90
How many ootids would be formed?
90
If one follows 90 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed?
90
If one follows 90 primary spermatocytes in an animal through their various stages of spermatogenesis, how many secondary spermatocytes would be formed?
90 x 2 = 180
How many spermatids would be formed?
90 x 4 = 360
Separation of sister chromatids occurs _______.
At anaphase in mitosis and anaphase II in meiosis
Anaphase
Cohesins break down Kinetochores move toward poles of cell
Prophase
Cohesins join sister chromatids of duplicated chromosome Tubulins assemble into spindle microtubule
Crossing Over
Crossing over occurs during early prophase I when homologous chromosomes loosely pair up along their lengths. Crossing over occurs only between nonsister chromatids within a homologous pair of chromosomes, not between the sister chromatids of a replicated chromosome. Crossing over is reduced near the centromere; segments that are not adjacent to the centromere (for example, segments near the ends of chromosomes) are more likely to cross over.
During interphase of the cell cycle, ________.
DNA content essentially doubles
Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II? (Note: Ignore any effects of crossing over.)
DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II ** During anaphase of both meiosis I and meiosis II, the DNA content (number of copies of chromosomes) in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set) **
Living organisms are categorized into two major groups based on the presence or absence of a nucleus. What group is defined by the presence of a nucleus?
Eukaryotic organism
TRUE OR FALSE: Haploid cells do not undergo mitosis
FALSE ** Both haploid & diploid cells CAN undergo mitosis **
TRUE OR FALSE: The longest stage of interphase is G2
FALSE ** Longest = S ** ** Shortest = G1 **
During which stage can cells either exit the cell cycle or become committed to completing the cell cycle?
G1 ** Cells can exit the cell cycle and enter G0 or be committed to initiate DNA synthesis late in G1 **
Meiosis I
Homologous chromosomes pair & then separate Thus, although the parent cell is diploid (containing two chromosome sets, 1 maternal and 1 paternal), each of the two daughter cells is haploid (containing only a single chromosome set)
Metaphase
Kinetochores are motionless in relation to poles of cell
Prometaphase
Microtubules attach to kinetochores
Does NOT occur during mitosis
Polar microtubules contract, pulling attached chromosomes toward the poles ** This describes the role of KINETOCHORE microtubules during anaphase. Polar microtubules LENGTHEN during anaphase, causing the cell to become elliptical **
Which condition is evaluated at the G2/M checkpoint?
Precise replication of DNA
Novel combinations of genes can arise from _______.
Reciprocal exchange of DNA between homologs during prophase I
Sister Chromatids
Separate during anaphase of mitosiscontain Identical nucleotide sequences prior to crossing Overseparate during anaphase II of meiosis ** Homologous chromosomes are a pair of chromosomes, one maternal and one paternal, that come together during fertilization. They have the same centromere position, and the same genetic loci (genes); however the DNA sequence is not identical. Crossing over between homologous chromosomes during prophase I of meiosis generates genetic diversity in the offspring. Homologous chromosomes pair up along the midline during metaphase I of meiosis, and move apart during anaphase I. Sister chromatids are the result of the replication of a single chromosome. They are identical in DNA sequence (apart from mutation or crossing over with a chromatid from a homologous chromosome). During metaphase of mitosis, chromosomes line up down the midline and sister chromatids separate during anaphase. In meiosis, sister chromatids separate during meiosis II **
Which of the following is true about the second meiotic division?
Sister chromatids are pulling apart.
Telophase
Spindle microtubules disassemble
TRUE OR FALSE: The end result of meiosis is four haploid daughter cells.
TRUE
Meiosis II
The sister chromatids separate The four daughter cells that result are haploid
What would most likely be true of these two chromosomes? Select all that apply.
They are homologous chromosomes. They have similar banding patterns. They would replicate synchronously during the S phase of the cell cycle.
Following fertilization by a normal sperm, what chromosome condition is temporarily created?
Trisomy
The centromere of a chromosome separates during ________.
anaphase
Name two cellular organelles, each containing genetic material, which are involved in either photosynthesis or respiration.
chloroplasts and mitochondria