Cell division occurs during this short phase, which generally involves two discrete processes: the contents of the nucleus (mainly the duplicated chromosomes) are evenly distributed to two daughter nuclei, and the cytoplasm divides in two.
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Mitotic Phase (M)
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DNA synthesis (or replication) occurs during this phase. At the beginning of the phase, each chromosome is single. At the end, after DNA replication, each chromosome consists of two sister chromatids.
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S phase
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Typically, this phase accounts for 90% of the cell cycle. It is a time of high metabolic activity. The cell grows by producing proteins and organelles, and chromosomes are replicated.
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Interphase
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This is when division of the nucleus occurs. The chromosomes that have been replicated are distributed to two daughter nuclei.
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Mitosis
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This third subphase of interphase is a period of metabolic activity and growth. During this phase the cell makes final preparations for division.
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G2 phase
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This is the portion of the cell cycle just after division, but before DNA synthesis. During this time the cell grows by producing proteins and organelles.
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G1 phase
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This is the step in the cell cycle when the cytoplasm divides in two.
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Cytokinesis
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Nucleoli are present during _____.
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Interphase:
The cytoplasm of a cell in late interphase contains two centrosomes, each of which may contain a pair of centrioles. In the nucleus, the chromosomes have been replicated during S phase, but are still dispersed in the form of chromatin. One or more nucleoli are present.
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Cytokinesis often, but not always, accompanies _____.
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Telophase:
During telophase, nuclear envelopes form around the identical sets of chromosomes at the two poles of the cell. The chromosomes uncoil and nucleoli appear in the two new nuclei. Meanwhile, cytokinesis begins, splitting the cytoplasm and separating the two daughter cells.
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Chromosomes become visible during _____.
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Prophase:
During prophase, the nucleoli disappear and chromatin fibers coil up to become discrete chromosomes. Each chromosome consists of two identical sister chromatids, joined at the centromere. Microtubules grow out from the centrosomes, initiating formation of the mitotic spindle.
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Spindle fibers attach to kinetochores during _____.
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Prometaphase:
During prometaphase, the nuclear envelope breaks into fragments. Some of the spindle fibers reach the chromosomes and attach to kinetochores, structures made of proteins and specific sections of DNA at the centromeres. Nonkinetochore microtubules overlap with those coming from the opposite pole.
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Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
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Anaphase:
Anaphase begins when the two centromeres of each chromosome come apart, separating the sister chromatids. Once separate, each sister chromatid is considered a full-fledged daughter chromosome. Motor proteins of the kinetochores "walk" the daughter chromosomes along the spindle microtubules toward opposite poles, and the microtubules shorten. At the same time, the spindle microtubules not attached to chromosomes lengthen, pushing the two poles farther apart and elongating the cell.
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During prophase a homologous pair of chromosomes consists of _____.
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two chromosomes and four chromatids
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Which of these is NOT a carcinogen?
A. cigarette smoke
B. fat
C. testosterone
D. UV light
E. all of the above are carcinogens
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E. all of the above are carcinogens
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_____ is a carcinogen that promotes colon cancer.
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Fat
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Mitosis vs Meiosis
overall function:
special function:
chromosome duplication:
PMAT (prophase, mete, ana, tele):
chromosome alignment:
number of cell divisions:
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cell division, cell division
growth and repair, gamete production
once before, once before
once, twice
singly, by homologous pairs
one, two
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Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II?
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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.
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Human gametes are produced by _____.
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Meiosis
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Normal human gametes carry _____ chromosomes.
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23
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Meiosis I produces _____ cells, each of which is _____.
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two .... haploid
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Meiosis II typically produces _____ cells, each of which is _____.
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four .... haploid
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During _____ sister chromatids separate.
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anaphase II
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At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.
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telophase I
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Synapsis occurs during _____.
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Prophase I
Prophase I begins with condensation of the chromosomes. Homologous chromosomes, each made up of two sister chromatids, come together in pairs. This pairing is called synapsis. Each chromosome pair is called a tetrad, a complex of four chromatids. Chromatids of homologous chromosomes cross over each other and exchange parts at chiasmata (singular, chiasma). Meanwhile, other cellular components prepare for the division of the nucleus. The centrosomes move away from each other, and spindle microtubules form between them. The nuclear envelope and nucleoli disperse. Finally, spindle microtubules capture the kinetochores that form on the chromosomes, and the chromosomes begin moving to the metaphase plate.
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Homologous chromosomes migrate to opposite poles during _____.
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anaphase I
During anaphase I, each pair of chromosomes is pulled apart and the homologous chromosomes move toward opposite poles. Note that sister chromatids remain attached at their centromeres and move as a unit toward the same pole.
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During _____ chromosomes align single file along the equator of a haploid cell.
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metaphase II
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At the end of _____ and cytokinesis there are four haploid cells.
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telophase II
In telophase II, nuclei form at opposite poles of each dividing cell, and cytokinesis splits the cells apart. Meiosis has produced four haploid cells, each with one set of chromosomes.
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During _____ a spindle forms in a haploid cell.
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prophase II
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What process is responsible for the independent assortment of alleles?
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meiosis
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How do cells acquire homologous chromosome pairs that carry the alleles that are independently assorted?
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fusion of gametes
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Which of the following statements most accurately describes the process of independent assortment?
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Alleles of different genes segregate from one another in a random manner
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True or false? The principle of independent assortment is best illustrated by events that take place during metaphase II, during which sister chromatids segregate independently of each other.
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false
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How many genetically unique types of gametes could be produced by an individual with the genotype RrYY?
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two, the gametes would be either RY or rY.
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Which of the following parental genotypes would yield a 1:1:1:1 phenotypic ratio in the offspring?
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AaBb, aabb
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Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?
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a combination of polygenic inheritance and environmental factors
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deletion
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is the loss of part of a chromosomal segment
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duplication
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is the repetition of a segment. The repeated segment may be located next to the original or at a different location, and its orientation may be the same as the original or the reverse.
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inversion
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is the removal of a segment followed by its reinsertion into the same chromosome in the reverse orientation.
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translocation
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is the transfer of a segment to a nonhomologous chromosome. Translocations may be reciprocal (two nonhomologous chromosomes exchange segments) or nonreciprocal (one chromosome transfers a segment without receiving one)
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What is a nondisjunction?
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An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell
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When can nondisjunction occur? Choose the best answer.
A. In mitosis, when sister chromatids fail to separate
B. All three answers are correct.
C. In meiosis, when homologous chromosomes fail to separate
D. In meiosis, when sister chromatids fail to separate
answer
B. All three answers are correct.
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Which syndrome is characterized by the XO chromosome abnormality?
answer
Turner syndrome
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What kind of cell results when a diploid and a haploid gamete fuse during fertilization?
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A triploid cell
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Of the following chromosomal abnormalities, which type is most likely to be viable in humans?
answer
Trisomy
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If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n ? 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?
answer
A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.
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If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n? 1 chromosomes, what type of error occurred?
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A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.
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Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete?
answer
1
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Humans are diploid and have 46 chromosomes. How many chromosomes are found in each human gamete?
answer
23
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_____ is the process by which haploid gametes form a diploid zygote.
answer
fertilization
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A particular diploid plant species has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have _____ set(s) of chromosomes.
answer
4
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Which of these terms applies to an organism with extra sets of chromosomes?
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polyploid
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Mutant tetraploid plants _____.
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are unable to interbreed with a diploid plant
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Most polyploid plants arise as a result of _____.
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hybridization
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In the 1950s, when Watson and Crick were working on their model of DNA, which concepts were well accepted by the scientific community?
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Genes are located on chromosomes.
Chromosomes are found in the nucleus.
Chromosomes are made up of protein and nucleic acid.
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What are the chemical components of a DNA molecule?
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sugars
phosphate groups
nitrogenous bases
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In the early 1950s, many researchers were racing to describe the structure of DNA using different approaches. Which of the following statements is true?
answer
Jim Watson and Francis Crick built theoretical models, incorporating current knowledge about chemical bonding and X-ray data.
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Early, flawed DNA models proposed by Watson and Crick and by Linus Pauling correctly described which property of DNA?
answer
DNA is composed of sugars, phosphates, and bases.
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What did Rosalind Franklin's famous photo 51 show?
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DNA is a helix
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Erwin Chargaff observed that the proportions of adenine (A) and thymine (T) bases were always equal, as were the proportion of guanine (G) and cytosine (C). Chargaff's observation suggests which of the following statements?
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The data suggest that A would always pair with T and G would always pair with C in a DNA molecule.
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What did the structure of DNA's double helix suggest about DNA's properties?
answer
DNA can be replicated by making complementary copies of each strand.
DNA stores genetic information in the sequence of its bases.
DNA can change. Errors in copying can result in changes in the DNA sequence that could be inherited by future generations.
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Who demonstrated that DNA is the genetic material of the T2 phage?
answer
Hershey and Chase
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The radioactive isotope 32P labels the T2 phage's _____.
answer
DNA
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Hershey and Chase used _____ to radioactively label the T2 phage's proteins.
answer
35S
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After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.
answer
labeled DNA ... DNA
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In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.
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thymine ... cytosine
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Which of these is a difference between a DNA and an RNA molecule?
answer
DNA is usually double-stranded, whereas RNA is usually single-stranded.
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In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.
answer
1...5
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Nucleic acids are assembled in the _____ direction.
answer
5 to 3
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After the replication is complete the new DNAs, called _____, are identical to eachother
answer
Daughter DNA
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the new DNA that grows continuously in the 5 to 3 direction is called the _____
answer
leading strand
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during DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is a called ____
answer
replication fork
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the enzyme that can replicate DNA is called
answer
DNA polymerase
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____ are short sections of DNA that are synthesized on the lagging strand of the replicating DNA
answer
okazaki fragments
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Short segments of newly synthesized DNA are joined into a continuous strand by _____.
answer
ligase
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After DNA replication is completed, _____.
answer
each new DNA double helix consists of one old DNA strand and one new DNA strand
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The action of helicase creates _____.
answer
replication forks and replication bubbles
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Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
answer
DNA polymerase can assemble DNA only in the 5' to 3' direction
Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled either in short 5' to 3' segments, which are later joined together by ligase, or be assembled continuously.
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An old DNA strand is used as a _____ for the assembly of a new DNA strand.
answer
template
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The first step in the replication of DNA is catalyzed by _____.
answer
helicase
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The synthesis of a new strand begins with the synthesis of a(n) _____.
answer
RNA primer complementary to a preexisting DNA strand
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What catalyzes DNA synthesis?
answer
DNA polymerase
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Which of the following statements about DNA synthesis is true?
answer
Primers are short sequences that allow the initiation of DNA synthesis.
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Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?
answer
Phosphate groups
The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis.
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Which of the following enzymes creates a primer for DNA polymerase?
answer
primase
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Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?
answer
Topoisomerase
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True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.
answer
true
question
DNA is a self-replicating molecule. What accounts for this important property of DNA?
answer
The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C.
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