review Flashcards
Chromosomes condense. The spindle apparatus
begins to form, and polar microtubules overlap each other
Prophase
In cells of many organisms, the nuclear envelope
disintegrates. Microtubules attach to the kinetochores
of chromosomes and begin moving them to the middle of the
spindle.
Prometaphase
All the chromosomes are positioned in the middle
of the spindle. The spindle is anchored to the cell membrane
by astral microtubules.
Metaphase
Sister chromatids are pulled apart by the disassembly
of kinetochore microtubules at the kinetochore. The
separated chromatids are now daughter chromosomes. The
spindle poles are moved farther apart to fully separate the replicated
chromosomes.
Anaphase
Telophase
Daughter chromosomes are fully separated and
are clustered at opposite poles of the spindle. A nuclear envelope
forms around each set and the chromosomes de-condense.
How Do Cells Replicate?
when a cell divides it must copy its chromosomes, separate the copies, and divide the cytoplasm to generate daughter cells such that each carries the same chromosomal complement as the parent.
interphase consists of s phase
is when chromosomes are replicated and gap phases called g1 and g2 when cells grow and prepare for division
eukaryotic cells divide by cycling through four phases
g1, s , g2, and M and enter a non replication phase called g0
eukaryotic cells divide by
alternating between interphase and M phase.
Which statement about the daughter cells following mitosis and cytokinesis is correct?
They are genetically identical with each other and with the
parent cell
Progression through the cell cycle is regulated by oscillations in
the concentration of which type of molecule?
cyclins
After the S phase, what comprises a single chromosome
two sister chromatids
What major events occur during anaphase of mitosis
Sister chromatids separate, and the spindle poles are pushed farther apart.
What evidence suggests that during anaphase, kinetochore
microtubules shorten at the kinetochore
Daughter chromosomes were observed to
move toward the pole faster than do the marked regions
of fluorescently labeled kinetochore microtubules.
Under normal conditions, what happens to the cell cycle if the chromosomes fail to separate properly at anaphase?
The cycle would arrest in M phase, and cytokinesis
would not occur.
Identify at least two events in the cell cycle that must be completed successfully for daughter cells to share an identical complement of chromosomes.
For daughter cells to have identical complements
of chromosomes, all the chromosomes must be
replicated during the S phase, the spindle apparatus
must connect with the kinetochores of each sister
chromatid in prometaphase, and the sister chromatids
of each replicated chromosome must be partitioned
in anaphase and fully separated into daughter cells
by cytokinesi
Explain how microinjection experiments supported the hypothesis
that specific molecules in the cytoplasm are involved in the
transition from interphase to M phase. What was the control for
this experiment?
Microinjection
experiments suggested that something in the cytoplasm
of M-phase cells activated the transition from
interphase to M phase. The control for this experiment
was to inject cytoplasm from a G2-arrested oocyte into
another G2-arrested oocyte
Why are most protein kinases considered regulatory proteins?
Protein kinases
phosphorylate proteins. Phosphorylation changes a
protein’s shape, altering its function (activating or
inactivating it). As a result, protein kinases regulate the
function of proteins.
Why are cyclins called cyclins? Explain their relationship to MPF activity
Cyclin concentrations
change during the cell cycle. At high concentration,
cyclins bind to a specific cyclin-dependent kinase (or
Cdk), forming a dimer. This dimer becomes active
MPF by changing its shape through the phosphorylation
(activating site) and dephosphorylation (inhibitory
site) of Cdk
A particular cell spends 4 hours in G1 phase, 2 hours
in S phase, 2 hours in G2 phase, and 30 minutes in M phase. If a
pulse–chase assay were performed with radioactive thymidine on
an asynchronous culture, what percentage of mitotic cells would
be radiolabeled after 9 hours?
adding up each phase allows you to determine
that the cell cycle is 8.5 hours long. After 9 hours,
the radiolabeled cells would have passed through a full
cycle and be in either S phase or G2—none would have
entered M phase
When fruit fly embryos first begin to develop, a large cell is
generated that contains over 8000 nuclei that are genetically identical with one another. What is most likely responsible for this
result?
The embryo passes through
multiple rounds of the cell cycle, but cytokinesis does not occur during M phases
What is most likely responsible for the reduction in death rates
over the past several years in cancers of the breast and prostate?
How is this related to the development of cancer?
Early detection of
cancers leads to a greater likelihood of survival. The
widespread implementation of breast and prostate exams
allows for the identification and removal of benign
tumors before they become malignant.
Cancer is primarily a disease of older people. Further, a group
of individuals may share a genetic predisposition to developing
certain types of cancer, yet vary a great deal in time of onset—or
not get the disease at all. What conclusion could be drawn based
on these observations? How does this relate to the requirements
for a cell to become cancerous?
Cancer
requires many defects. Older cells have had more time
to accumulate defects. Individuals with a genetic predisposition
to cancer start out with some cancer-related defects,
but this does not mean that the additional defects
required for cancer to occur will develop
In multicellular organisms, nondividing cells stay in G0 phase. For the
cell, why is it better to be held in G1 rather than S, G2, or M phase
G1 cells have not replicated their DNA in preparation for
division.
In the roundworm Ascaris, eggs and sperm have two
chromosomes, but all other cells have four. Observations such asthis inspired which important hypothesis?
Before gamete formation, a special type of cell division leads to a halving of chromosome number.
What are homologous chromosomes?
chromosomes that are similar in their size, shape, and gene
content
What is a bivalent?
a group of four chromatids produced when homologs synapse
What is an outcome of genetic recombination
the new combination of maternal and paternal chromosome
segments that results when homologs cross over
What proportion of chromosomes in a human skin cell are
paternal chromosomes
1/2
Meiosis II is similar to _____.
mitosis.
Explain the relationship between homologous chromosomes and
the relationship between sister chromatids
Homologous chromosomes are similar in
size, shape, and gene content, and originate from different
parents. Sister chromatids are exact copies of a
chromosome that are generated when chromosomes are
replicated (S phase of the cell cycle
Lay four pens and four pencils on a tabletop, and imagine that they
represent replicated chromosomes in a diploid cell where n = 2.
Explain the phases of meiosis II by moving the pens and pencils
around. (If you don’t have enough pens and pencils, use strips of
paper or fabric.)
The four pens
represent the chromatids in one replicated homologous
pair; the four pencils, the chromatids in a different homologous
pair. To simulate meiosis II, make two “haploid
cells”—each with a pair of pens and a pair of pencils
representing two replicated chromosomes (one of each
type in this species). Line them up in the middle of the
cell; then separate the two pens and the two pencils in
each cell such that one pen and one pencil go to each of
four daughter cell
Meiosis is called a reduction division, but all the reduction occurs during meiosis I—no reduction occurs during meiosis II. Explain
why meiosis I is a reduction division but meiosis II is not.
Meiosis I is a reduction
division because homologs separate—daughter cells
have just one of each type of chromosome instead of
two. Meiosis II is not a reduction division because sister
chromatids separate— daughter cells have unreplicated
chromosomes instead of replicated chromosomes, but
still just one of each type.
Dogs have 78 chromosomes in their diploid cells. If a diploid dog
cell enters meiosis, how many chromosomes and chromatids will
be present in each daughter cell at the end of meiosis I?
39 chromosomes and 78 chromatids
Triploid (3n) watermelons are produced by crossing a tetraploid
(4n) strain with a diploid (2n) plant. Briefly explain why this
mating produces a triploid individual. Why can mitosis proceed
normally in triploid cells, but meiosis cannot
Tetraploids
produce diploid gametes, which combine with a haploid
gamete from a diploid individual to form a triploid
offspring. Mitosis proceeds normally in triploid cells
because mitosis doesn’t require forming pairs of chromosomes.
But during meiosis in a triploid, homologous
chromosomes can’t pair up correctly. The third set of
chromosomes does not have a homologous partner to
pair with
Some plant breeders are concerned about the susceptibility of
asexually cultivated plants, such as seedless bananas, to new strains
of disease-causing bacteria, viruses, or fungi. Briefly explain their
concern by discussing the differences in the genetic “outcomes” of
asexual and sexual reproduction
Asexually produced individuals
are genetically identical, so if one is susceptible to a new
disease, all are. Sexually produced individuals are genetically
unique, so if a new disease strain evolves, at least
some plants are likely to be resistant
The gibbon has 44 chromosomes per diploid set, and the siamang
has 50 chromosomes per diploid set. In the 1970s a chance
mating between a male gibbon and a female siamang produced an
offspring. Predict how many chromosomes were observed in the
somatic cells of the offspring. Do you predict that this individual
would be able to form viable gametes? Why or why not
The gibbon would have 22 chromosomes in
each gamete, and the siamang would have 25. Each somatic
cell of the offspring would have 47 chromosomes.
The offspring should be sterile because it has some
chromosomes that would not form homologous pairs at
prophase I of meiosis.
Meiosis results in a reassortment of maternal and paternal
chromosomes. If n = 3 for a given organism, there are eight
different combinations of paternal and maternal chromosomes. If
no crossing over occurs, what is the probability that a gamete will
receive only paternal chromosomes?
1/8
Some researchers hypothesize that older women are less responsive
to triggers of spontaneous abortion than younger women. How
could the data shown in Figure 13.13, which graphs a mother’s age versus the incidence of Down syndrome, be used to support this
hypothesis?
Aneuploidy is
the major cause of spontaneous abortion. If spontaneous
abortion is rare in older women, it would result in a
higher incidence of aneuploid conditions such as Down
syndrome in older women
A species of rotifer, a small freshwater invertebrate, abandoned sexual reproduction millions of years ago. A remarkable feature
of the rotifer’s life cycle is its ability to withstand extreme drying. When the rotifer’s watery environment dries out, so does there rotifer, and it can be blown in the wind to a new environment. Once blown to water, the rotifer rehydrates and resumes an active life. A major pathogen of these rotifers is a species of fungus. Some scientists hypothesize that fungus-infected rotifers rid themselves of the pathogen when they dry.
Design an experimental study to test this hypothesis.
when mendal began his work there were two leading hypothesis of inheritance
blending inheritance and the inheritance of
acquired characteristics.
In studies of how traits are inherited, what makes certain species
candidates for model organisms?
They are easy to maintain, have a short life cycle, produce
many offspring, and yield data that are relevant to many other
organisms
Why is the allele for wrinkled seed shape in garden peas
considered recessive?
The trait associated with the allele is not expressed in
heterozygotes.
The alleles found in haploid organisms cannot be dominant or
recessive. Why?
Dominance and recessiveness describe which allele is expressed
in phenotype when different alleles occur in the same individual
Why can you infer that individuals that are “pure line” are
homozygous for the gene in question?
Because no other phenotype is ever observed in a pure-line
population, this implies that only one allele is present
The genes for the traits that Mendel worked with are either
located on different chromosomes or so far apart on the same
chromosome that crossing over almost always occurs between
them. How did this circumstance help Mendel recognize the
principle of independent assortment?
Otherwise, his dihybrid crosses would not have produced a
9 : 3 : 3 : 1 ratio of F2 phenotypes.
What is meant by the claim that Mendel worked with the simplest
possible genetic system?
Discrete traits, two alleles, simple dominance and recessiveness,
no sex chromosomes, and unlinked genes are the simplest
situation known.
Mendel’s rules do not correctly predict patterns of inheritance
for tightly linked genes or the inheritance of alleles that show
incomplete dominance. Does this mean that his hypotheses are
incorrect?
No, it just means that his hypotheses are limited to certain
conditions.
The artificial sweetener NutraSweet consists of a phenylalanine
molecule linked to aspartic acid. The labels of diet sodas that
contain NutraSweet include a warning to people with PKU. Why?
People with PKU have to avoid phenylalanine in their diet.
When Sutton and Boveri published the chromosome theory of
inheritance, research on meiosis had not yet established that
paternal and maternal homologs of different chromosomes
assort independently. Then, in 1913, Elinor Carothers published
a paper about a grasshopper species with an unusual karyotype:
One chromosome had no homolog (meaning no pairing partner
at meiosis I); another chromosome had homologs that could be
distinguished under the light microscope. If chromosomes assort
independently, how often should Carothers have observed each of
the four products of meiosis shown in the following figure?
The four types of gametes should be observed to occur at equal
frequencies.
Which of the following is the strongest evidence that a trait might
be influenced by polygenic inheritance
The trait shows quantitative variation.
In peas, purple flowers are dominant to white. If a purpleflowered,
heterozygous plant were crossed with a white-flowered
plant, what is the expected ratio of genotypes and phenotypes
among the F1 offspring? If two of the purple-flowered F1 offspring
were randomly selected and crossed, what is the expected ratio of
genotypes and phenotypes among the F2 offspring?
3/4; 1/256 (see BioSkills 5 in Appendix B); 1/2
(the probabilities of transmitting the alleles or having
sons does not change over time). 14
In garden peas, yellow seeds (Y) are dominant to green seeds
(y), and inflated pods (I) are dominant to constricted pods (i).
Suppose you have crossed YYII parents with yyii parents.
Draw the F1 Punnett square and predict the expected F1
phenotype(s).
List the genotype(s) of gametes produced by F1 individuals.
Draw the F2 Punnett square. Based on this Punnett square,
predict the expected phenotype(s) in the F2 generation and the
expected frequency of each phenotype.
Yes—there would be
some individuals with yellow seeds and constricted pods
and with green seeds and inflated pods
How can biological fitness be estimated
Count the number of healthy, fertile offspring produced by
different individuals in a population
Some traits are considered vestigial because they
existed long ago.
false
What is an adaptation?
a trait that improves the fitness of its bearer, compared with
individuals without the trait
