Bio Exam
In a mating between two individuals that are heterozygous for a recessive lethal allele that is expressed in utero, what genotypic ratio (homozygous dominant:heterozygous:homozygous recessive) would you expect to observe in the offspring? 1:2:1 3:1:1 1:2:0 0:2:1
0:2:0
What steps are necessary for Cdk to become fully active?
Cdk must bind to a cyclin, and it must be phosphorylated in the correct position to become fully active.
Which protein is a positive regulator that phosphorylates other proteins when activated? p53 retinoblastoma protein (Rb) cyclin cyclin-dependent kinase (Cdk)
Cyclin dependent kinase (Cdk)
At which of the cell cycle checkpoints do external forces have the greatest influence? G1 checkpoint G2 checkpoint M checkpoint G0 checkpoint
G1 checkpoint
__________ are changes to the order of nucleotides in a segment of DNA that codes for a protein. Proto-oncogenes Tumor suppressor genes Gene mutations Negative regulators
Gene mutations
What is the function of the fused kinetochore found on sister chromatids in prometaphase I?
In metaphase I, the homologous chromosomes line up at the metaphase plate. In anaphase I, the homologous chromosomes are pulled apart and move to opposite poles. Sister chromatids are not separated until meiosis II. The fused kinetochore formed during meiosis I ensures that each spindle microtubule that binds to the tetrad will attach to both sister chromatids.
What phase of mitotic interphase is missing from meiotic interkinesis? G0 phase G1 phase S phase G2 phase
S phase
Eukaryotic chromosomes are thousands of times longer than a typical cell. Explain how chromosomes can fit inside a eukaryotic nucleus.
The DNA double helix is wrapped around histone proteins to form structures called nucleosomes. Nucleosomes and the linker DNA in between them are coiled into a 30-nm fiber. During cell division, chromatin is further condensed by packing proteins.
Describe the general conditions that must be met at each of the three main cell cycle checkpoints.
The G1 checkpoint monitors adequate cell growth, the state of the genomic DNA, adequate stores of energy, and materials for S phase. At the G2 checkpoint, DNA is checked to ensure that all chromosomes were duplicated and that there are no mistakes in newly synthesized DNA. Additionally, cell size and energy reserves are evaluated. The M checkpoint confirms the correct attachment of the mitotic spindle fibers to the kinetochores.
Name the common components of eukaryotic cell division and binary fission.
The common components of eukaryotic cell division and binary fission are DNA duplication, segregation of duplicated chromosomes, and division of the cytoplasmic contents.
Which type of life cycle has both a haploid and diploid multicellular stage? A) asexual B) diploid-dominant C) haploid-dominant D) alternation of generations
alternation of generations
A mutated gene that codes for an altered version of Cdk that is active in the absence of cyclin is a(n) _____. kinase inhibitor. tumor suppressor gene. proto-oncogene. oncogene.
oncogene
Which negative regulatory molecule can trigger cell suicide (apoptosis) if vital cell cycle events do not occur? p53 p21 retinoblastoma protein (Rb) cyclin-dependent kinase (Cdk)
p53
The observable traits expressed by an organism are described as its ________. phenotype genotype alleles zygote
phenotype
Which of the following events does not occur during some stages of interphase? DNA duplication organelle duplication increase in cell size separation of sister chromatids
separation of sister chromatids
Identical copies of chromatin held together by cohesin at the centromere are called _____. histones. nucleosomes. chromatin. sister chromatids.
sister chromatids
Which recombination frequency corresponds to perfect linkage and violates the law of independent assortment? 0 0.25 0.50 0.75
0
If a muscle cell of a typical organism has 32 chromosomes, how many chromosomes will be in a gamete of that same organism? 8 16 32 64
16
Assuming no gene linkage, in a dihybrid cross of AABB x aabb with AaBb F1 heterozygotes, what is the ratio of the F1 gametes (AB, aB, Ab, ab) that will give rise to the F2 offspring? 1:1:1:1 1:3:3:1 1:2:2:1 4:3:2:1
1:1:1:1
Consider a cross to investigate the pea pod texture trait, involving constricted or inflated pods. Mendel found that the traits behave according to a dominant/recessive pattern in which inflated pods were dominant. If you performed this cross and obtained 650 inflated-pod plants in the F2 generation, approximately how many constricted-pod plants would you expect to have? 600 165 217 468
217
Explain the difference between a proto-oncogene and a tumor suppressor gene.
A proto-oncogene is a segment of DNA that codes for one of the positive cell cycle regulators. If that gene becomes mutated so that it produces a hyperactivated protein product, it is considered an oncogene. A tumor suppressor gene is a segment of DNA that codes for one of the negative cell cycle regulators. If that gene becomes mutated so that the protein product becomes less active, the cell cycle will run unchecked. A single oncogene can initiate abnormal cell divisions; however, tumor suppressors lose their effectiveness only when both copies of the gene are damaged.
In a comparison of the stages of meiosis to the stages of mitosis, which stages are unique to meiosis and which stages have the same events in both meiosis and mitosis?
All of the stages of meiosis I, except possibly telophase I, are unique because homologous chromosomes are separated, not sister chromatids. In some species, the chromosomes do not decondense and the nuclear envelopes do not form in telophase I. All of the stages of meiosis II have the same events as the stages of mitosis, with the possible exception of prophase II. In some species, the chromosomes are still condensed and there is no nuclear envelope. Other than this, all processes are the same.
Describe how the duplicated bacterial chromosomes are distributed into new daughter cells without the direction of the mitotic spindle.
As the chromosome is being duplicated, each origin moves away from the starting point of replication. The chromosomes are attached to the cell membrane via proteins; the growth of the membrane as the cell elongates aids in their movement.
Imagine you are performing a cross involving seed color in garden pea plants. What F1 offspring would you expect if you cross true-breeding parents with green seeds and yellow seeds? Yellow seed color is dominant over green. A) 100 percent yellow-green seeds B) 100 percent yellow seeds C) 50 percent yellow, 50 percent green seeds D) 25 percent green, 75 percent yellow seeds
B) 100 percent yellow seeds
The gene for flower position in pea plants exists as axial or terminal alleles. Given that axial is dominant to terminal, list all of the possible F1 and F2 genotypes and phenotypes from a cross involving parents that are homozygous for each trait. Express genotypes with conventional genetic abbreviations.
Because axial is dominant, the gene would be designated as A. F1 would be all heterozygous Aa with axial phenotype. F2 would have possible genotypes of AA, Aa, and aa; these would correspond to axial, axial, and terminal phenotypes, respectively.
What is a likely evolutionary advantage of sexual reproduction over asexual reproduction? A) Sexual reproduction involves fewer steps. B) There is a lower chance of using up the resources in a given environment. C) Sexual reproduction results in variation in the offspring. D) Sexual reproduction is more cost-effective.
C) Sexual reproduction results in variation in the offspring.
Which of the following is not true in regard to crossover? A)Spindle microtubules guide the transfer of DNA across the synaptonemal complex. B)Non-sister chromatids exchange genetic material. C)Chiasmata are formed. D)Recombination nodules mark the crossover point.
C)Chiasmata are formed.
Use the probability method to calculate the genotypes and genotypic proportions of a cross between AABBCc and Aabbcc parents.
Considering each gene separately, the cross at A will produce offspring of which half are AA and half are Aa; B will produce all Bb; C will produce half Cc and half cc. Proportions then are (1/2) × (1) × (1/2), or 1/4 AABbCc; continuing for the other possibilities yields 1/4 AABbcc, 1/4 AaBbCc, and 1/4 AaBbcc. The proportions therefore are 1:1:1:1.
How many different offspring genotypes are expected in a trihybrid cross between parents heterozygous for all three traits when the traits behave in a dominant and recessive pattern? How many phenotypes? A) 64 genotypes; 16 phenotypes B) 16 genotypes; 64 phenotypes C) 8 genotypes; 27 phenotypes D) 27 genotypes; 8 phenotypes
D) 27 genotypes; 8 phenotypes
Describe the process that results in the formation of a tetrad.
During the meiotic interphase, each chromosome is duplicated. The sister chromatids that are formed during synthesis are held together at the centromere region by cohesin proteins. All chromosomes are attached to the nuclear envelope by their tips. As the cell enters prophase I, the nuclear envelope begins to fragment, and the proteins holding homologous chromosomes locate each other. The four sister chromatids align lengthwise, and a protein lattice called the synaptonemal complex is formed between them to bind them together. The synaptonemal complex facilitates crossover between non-sister chromatids, which is observed as chiasmata along the length of the chromosome. As prophase I progresses, the synaptonemal complex breaks down and the sister chromatids become free, except where they are attached by chiasmata. At this stage, the four chromatids are visible in each homologous pairing and are called a tetrad.
p53 can trigger apoptosis if certain cell cycle events fail. How does this regulatory outcome benefit a multicellular organism?
If a cell has damaged DNA, the likelihood of producing faulty proteins is higher. The daughter cells of such a damaged parent cell would also produce faulty proteins that might eventually become cancerous. If p53 recognizes this damage and triggers the cell to self-destruct, the damaged DNA is degraded and recycled. No further harm comes to the organism. Another healthy cell is triggered to divide instead.
What cell cycle events will be affected in a cell that produces mutated (non-functional) cohesin protein?
If cohesin is not functional, chromosomes are not packaged after DNA replication in the S phase of interphase. It is likely that the proteins of the centromeric region, such as the kinetochore, would not form. Even if the mitotic spindle fibers could attach to the chromatids without packing, the chromosomes would not be sorted or separated during mitosis.
Outline the steps that lead to a cell becoming cancerous.
If one of the genes that produces regulator proteins becomes mutated, it produces a malformed, possibly non-functional, cell cycle regulator, increasing the chance that more mutations will be left unrepaired in the cell. Each subsequent generation of cells sustains more damage. The cell cycle can speed up as a result of the loss of functional checkpoint proteins. The cells can lose the ability to self-destruct and eventually become "immortalized."
List some reasons why a cell that has just completed cytokinesis might enter the G0 phase instead of the G1 phase.
Many cells temporarily enter G0 until they reach maturity. Some cells are only triggered to enter G1 when the organism needs to increase that particular cell type. Some cells only reproduce following an injury to the tissue. Some cells never divide once they reach maturity.
Using diagrams, illustrate how nondisjunction can result in an aneuploid zygote.
Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, resulting in an abnormal chromosome number. Nondisjunction may occur during meiosis I or meiosis II.
Explain the roles of the positive cell cycle regulators compared to the negative regulators.
Positive cell regulators such as cyclin and Cdk perform tasks that advance the cell cycle to the next stage. Negative regulators such as Rb, p53, and p21 block the progression of the cell cycle until certain events have occurred.
Explain how the random alignment of homologous chromosomes during metaphase I contributes to the variation in gametes produced by meiosis.
Random alignment leads to new combinations of traits. The chromosomes that were originally inherited by the gamete-producing individual came equally from the egg and the sperm. In metaphase I, the duplicated copies of these maternal and paternal homologous chromosomes line up across the center of the cell. The orientation of each tetrad is random. There is an equal chance that the maternally derived chromosomes will be facing either pole. The same is true of the paternally derived chromosomes. The alignment should occur differently in almost every meiosis. As the homologous chromosomes are pulled apart in anaphase I, any combination of maternal and paternal chromosomes will move toward each pole. The gametes formed from these two groups of chromosomes will have a mixture of traits from the individual's parents. Each gamete is unique.
Rb is a negative regulator that blocks the cell cycle at the G1 checkpoint until the cell achieves a requisite size. What molecular mechanism does Rb employ to halt the cell cycle?
Rb is active when it is dephosphorylated. In this state, Rb binds to E2F, which is a transcription factor required for the transcription and eventual translation of molecules required for the G1/S transition. E2F cannot transcribe certain genes when it is bound to Rb. As the cell increases in size, Rb becomes phosphorylated, inactivated, and releases E2F. E2F can then promote the transcription of the genes it controls, and the transition proteins will be produced.
Explain how the Chromosomal Theory of Inheritance helped to advance our understanding of genetics.
The Chromosomal Theory of Inheritance proposed that genes reside on chromosomes. The understanding that chromosomes are linear arrays of genes explained linkage, and crossing over explained recombination.
Use a Punnett square to predict the offspring in a cross between a dwarf pea plant (homozygous recessive) and a tall pea plant (heterozygous). What is the phenotypic ratio of the offspring?
The Punnett square would be 2 × 2 and will have T and T along the top, and T and t along the left side. Clockwise from the top left, the genotypes listed within the boxes will be Tt, Tt, tt, and tt. The phenotypic ratio will be 1 tall:1 dwarf.
In Section 12.3, "Laws of Inheritance," an example of epistasis was given for the summer squash. Cross white WwYy heterozygotes to prove the phenotypic ratio of 12 white:3 yellow:1 green that was given in the text.
The cross can be represented as a 4 × 4 Punnett square, with the following gametes for each parent: WY, Wy, wY, and wy. For all 12 of the offspring that express a dominant W gene, the offspring will be white. The three offspring that are homozygous recessive for w but express a dominant Y gene will be yellow. The remaining wwyy offspring will be green.
Describe one of the reasons why the garden pea was an excellent choice of model system for studying inheritance.
The garden pea is sessile and has flowers that close tightly during self-pollination. These features help to prevent accidental or unintentional fertilizations that could have diminished the accuracy of Mendel's data.
What is the relationship between a genome, chromosomes, and genes?
The genome consists of the sum total of an organism's chromosomes. Each chromosome contains hundreds and sometimes thousands of genes, segments of DNA that code for a polypeptide or RNA, and a large amount of DNA with no known function.
Chemotherapy drugs such as vincristine and colchicine disrupt mitosis by binding to tubulin (the subunit of microtubules) and interfering with microtubule assembly and disassembly. Exactly what mitotic structure is targeted by these drugs and what effect would that have on cell division?
The mitotic spindle is formed of microtubules. Microtubules are polymers of the protein tubulin; therefore, it is the mitotic spindle that is disrupted by these drugs. Without a functional mitotic spindle, the chromosomes will not be sorted or separated during mitosis. The cell will arrest in mitosis and die.
Describe the similarities and differences between the cytokinesis mechanisms found in animal cells versus those in plant cells.
There are very few similarities between animal cell and plant cell cytokinesis. In animal cells, a ring of actin fibers is formed around the periphery of the cell at the former metaphase plate (cleavage furrow). The actin ring contracts inward, pulling the plasma membrane toward the center of the cell until the cell is pinched in two. In plant cells, a new cell wall must be formed between the daughter cells. Due to the rigid cell walls of the parent cell, contraction of the middle of the cell is not possible. Instead, a phragmoplast first forms. Subsequently, a cell plate is formed in the center of the cell at the former metaphase plate. The cell plate is formed from Golgi vesicles that contain enzymes, proteins, and glucose. The vesicles fuse and the enzymes build a new cell wall from the proteins and glucose. The cell plate grows toward and eventually fuses with the cell wall of the parent cell.
How would you perform a reciprocal cross for the characteristic of stem height in the garden pea?
Two sets of P0 parents would be used. In the first cross, pollen would be transferred from a true-breeding tall plant to the stigma of a true-breeding dwarf plant. In the second cross, pollen would be transferred from a true-breeding dwarf plant to the stigma of a true-breeding tall plant. For each cross, F1 and F2 offspring would be analyzed to determine if offspring traits were affected according to which parent donated each trait.
If the M checkpoint is not cleared, what stage of mitosis will be blocked? prophase prometaphase metaphase anaphase
anaphase
FtsZ proteins direct the formation of a _______ that will eventually form the new cell walls of the daughter cells. contractile ring cell plate cytoskeleton septum
cell plate
The fusing of Golgi vesicles at the metaphase plate of dividing plant cells forms what structure? cell plate actin ring cleavage furrow mitotic spindle
cell plate
At metaphase I, homologous chromosomes are connected only at what structures? chiasmata recombination nodules microtubules kinetochores
chiasmata
The first suggestion that chromosomes may physically exchange segments came from the microscopic identification of ________. synapsis sister chromatids chiasmata alleles
chiasmata
The first level of DNA organization in a eukaryotic cell is maintained by which molecule? cohesin condensin chromatin histone
histone
A recessive trait will be observed in individuals that are ________ for that trait. heterozygous homozygous or heterozygous homozygous diploid
homozygous
If black and white true-breeding mice are mated and the result is all gray offspring, what inheritance pattern would this be indicative of? A) dominance B) codominance C) multiple alleles D) incomplete dominance
incomplete dominance
The part of meiosis that is similar to mitosis is ________. meiosis I anaphase I meiosis II interkinesis
meiosis II
The ABO blood groups in humans are expressed as the IA, IB, and i alleles. The IA allele encodes the A blood group antigen, IB encodes B, and i encodes O. Both A and B are dominant to O. If a heterozygous blood type A parent (IAi) and a heterozygous blood type B parent (IBi) mate, one quarter of their offspring will have AB blood type (IAIB) in which both antigens are expressed equally. Therefore, ABO blood groups are an example of: A) multiple alleles and incomplete dominance B)codominance and incomplete dominance C) incomplete dominance only D) multiple alleles and codominance
multiple alleles and codominance
Attachment of the mitotic spindle fibers to the kinetochores is a characteristic of which stage of mitosis? prophase prometaphase metaphase anaphase
prometaphase
The chromosomes become visible under a light microscope during which stage of mitosis? prophase prometaphase metaphase anaphase
prophase
Which is one of the seven characteristics that Mendel observed in pea plants? flower size seed texture leaf shape stem color
seed texture
Which recombination frequency corresponds to independent assortment and the absence of linkage? 0 0.25 0.50 0.75
.50
Which of the following codes describes position 12 on the long arm of chromosome 13? 13p12 13q12 12p13 12q13
13q12
X-linked recessive traits in humans (or in Drosophila) are observed ________. A)in more males than females B) in more females than males C) in males and females equally D) in different distributions depending on the trait
A)in more males than females
A diploid cell has_______ the number of chromosomes as a haploid cell. a)one-fourth b)half c)twice d)four times
C- twice
Briefly describe the events that occur in each phase of interphase.
During G1, the cell increases in size, the genomic DNA is assessed for damage, and the cell stockpiles energy reserves and the components to synthesize DNA. During the S phase, the chromosomes, the centrosomes, and the centrioles (animal cells) duplicate. During the G2 phase, the cell recovers from the S phase, continues to grow, duplicates some organelles, and dismantles other organelles.
Explain epistatis in terms of its Greek-language roots "standing upon."
Epistasis describes an antagonistic interaction between genes wherein one gene masks or interferes with the expression of another. The gene that is interfering is referred to as epistatic, as if it is "standing upon" the other (hypostatic) gene to block its expression.
Compare and contrast a human somatic cell to a human gamete.
Human somatic cells have 46 chromosomes: 22 pairs and 2 sex chromosomes that may or may not form a pair. This is the 2n or diploid condition. Human gametes have 23 chromosomes, one each of 23 unique chromosomes, one of which is a sex chromosome. This is the n or haploid condition.
Can a human male be a carrier of red-green color blindness?
No, males can only express color blindness. They cannot carry it because an individual needs two X chromosomes to be a carrier.
Which molecule is a Cdk inhibitor that is controlled by p53? cyclin anti-kinase Rb p21
P21
List the regulatory mechanisms that might be lost in a cell producing faulty p53.
Regulatory mechanisms that might be lost include monitoring of the quality of the genomic DNA, recruiting of repair enzymes, and the triggering of apoptosis.
Chromosomes are duplicated during what stage of the cell cycle? G1 phase S phase prophase prometaphase
S phase
Abnormalities in the number of X chromosomes tends to have milder phenotypic effects than the same abnormalities in autosomes because of ________. A) deletions B) nonhomologous recombination C) synapsis D) X inactivation
X inactivation
List and briefly describe the three processes that lead to variation in offspring with the same parents.
a. Crossover occurs in prophase I between non-sister homologous chromosomes. Segments of DNA are exchanged between maternally derived and paternally derived chromosomes, and new gene combinations are formed. b. Random alignment during metaphase I leads to gametes that have a mixture of maternal and paternal chromosomes. c. Fertilization is random, in that any two gametes can fuse.
Compare the three main types of life cycles in multicellular organisms and give an example of an organism that employs each.
a. In the haploid-dominant life cycle, the multicellular stage is haploid. The diploid stage is a spore that undergoes meiosis to produce cells that will divide mitotically to produce new multicellular organisms. Fungi have a haploid-dominant life cycle. b. In the diploid-dominant life cycle, the most visible or largest multicellular stage is diploid. The haploid stage is usually reduced to a single cell type, such as a gamete or spore. Animals, such as humans, have a diploid-dominant life cycle. c. In the alternation of generations life cycle, there are both haploid and diploid multicellular stages, although the haploid stage may be completely retained by the diploid stage. Plants have a life cycle with alternation of generations.
What is the main prerequisite for clearance at the G2 checkpoint? cell has reached a sufficient size an adequate stockpile of nucleotides accurate and complete DNA replication proper attachment of mitotic spindle fibers to kinetochores
accurate and complete DNA replication
Separation of the sister chromatids is a characteristic of which stage of mitosis? prometaphase metaphase anaphase telophase
anaphase
At which stage of meiosis are sister chromatids separated from each other? prophase I prophase II anaphase I anaphase II
anaphase II
Mendel performed hybridizations by transferring pollen from the _______ of the male plant to the female ova. anther pistil stigma seed
anther
Many of the negative regulator proteins of the cell cycle were discovered in what type of cells? gametes cells in G0 cancer cells stem cells
cancer cells
By definition, a pericentric inversion includes the ________. centromere chiasma telomere synapse
centromere
The mitotic spindles arise from which cell structure? centromere centrosome kinetochore cleavage furrow
centrosome
Meiosis produces ________ daughter cells. two haploid two diploid four haploid four diploid
four haploid
An organism's traits are determined by the specific combination of inherited _____. cells. genes. proteins. chromatids.
genes
Fungi typically display which type of life cycle? A) diploid-dominant B) haploid-dominant C) alternation of generations D) asexual
haploid-dominant
Which eukaryotic cell cycle event is missing in binary fission? cell growth DNA duplication karyokinesis cytokinesis
karyokinesis
The genotype XXY corresponds to Klinefelter syndrome Turner syndrome Triplo-X Jacob syndrome
klinefelter syndrome
In agriculture, polyploid crops (like coffee, strawberries, or bananas) tend to produce ________. more uniformity more variety larger yields smaller yields
larger yields
Assume a pericentric inversion occurred in one of two homologs prior to meiosis. The other homolog remains normal. During meiosis, what structure—if any—would these homologs assume in order to pair accurately along their lengths? A) V formation B) cruciform C) loop D) pairing would not be possible
loop
The forked line and probability methods make use of what probability rule? test cross product rule monohybrid rule sum rule
product rule
A gene that codes for a positive cell cycle regulator is called a(n) _____. kinase inhibitor. tumor suppressor gene. proto-oncogene. oncogene.
proto-oncogene
A diploid, multicellular life-cycle stage that gives rise to haploid cells by meiosis is called a ________. sporophyte gametophyte spore gamete
sporophyte
What structure is most important in forming the tetrads? centromere synaptonemal complex chiasma kinetochore
synaptonemal complex
Unpacking of chromosomes and the formation of a new nuclear envelope is a characteristic of which stage of mitosis? prometaphase metaphase anaphase telophase
telophase
