MC Prep
In a population of 100 inbred, genotypically identical rice plants, variance for grain yield is 2.66. What is the heritability for yield? Would you advise a rice breeder to improve yield in this strain of rice plants by selection?
0, No, Selection would not be effective in this strain of rice.
Achondroplasia is a dominant trait that causes a characteristic form of dwarfism. In a survey of 1.5×10^5 births, 20 infants with achondroplasia were identified. Of these affected infants, 1818 had affected parents, while 22 had normal parents.
0.000007
Assuming that p = 0.3 for a population in Hardy-Weinberg equilibrium, what would be the expected frequency of heterozygotes for the involved allelic pair?
0.42
Suppose that a given gene undergoes a mutation to a dominant allele such that 2 out of 100,000 offspring exhibit the new mutant phenotype. Assuming that these offspring are heterozygous, what is the mutation rate for the gene?
1/100,000
How can we ascertain the number of polygenes involved in the inheritance of a quantitative trait? Select the two correct statements.
1/4n, where n=the number of polygenes if the raio of F2 individuals resembling either of the two extreme P1 phenotypes can be determined (2n+1), where (2n+1) is the number of possible phenotypes and n equals the number of additive loci
Suppose that ear length in rabbits is controlled by two additive genes, each of which has two alleles. A true-breeding female (aabb) with 6-cm ears is mated to a true-breeding male (AABB) with 16-cm ears.Predict the ear length of the F1 generation. (Note: Assume that each allele contributes equally to ear length, and the genes segregate independently. Also assume that environmental influence on ear length is negligible.) Use the information from Part B to determine which genotype(s) in the F2 generation would produce an ear length of 13.5 cm.
11cm AaBB, AABb
Erma and Harvey were a compatible barnyard pair, but a curious sight. Harvey's tail was only 6 cmcm long, while Erma's was 30 cmcm. Their F1F1 piglet offspring all grew tails that were 18 cmcm. When inbred, an F2F2 generation resulted in many piglets (Erma and Harvey's grandpigs), whose tails ranged in 4-cmcm intervals from 6 to 30 cmcm (6, 10, 14, 18, 22, 26, and 30). Most had 18-cmcm tails, while 1/641/64 had 6-cmcm tails and 1/641/64 had 30-cmcm tails. If the 18−cm F1 pig with genotype AAbbCc is mated with one of the 6−cm F2 pigs, what phenotypic ratio would be predicted if many offspring resulted?
14 cm/ 10 cm = 1 :1
A certain form of albinism in humans is recessive and autosomal. Assume that 1% of the individuals in a given population are albino. Assuming that the population is in Hardy-Weinberg equilibrium, what percentage of the individuals in this population is expected to be heterozygous?
18%
In a population that meets the Hardy-Weinberg equilibrium assumptions, 81% of the individuals are homozygous for a recessive allele. What percentage of the individuals would be expected to be heterozygous for this locus in the next generation?
18%
A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red F1.When the F1 plants are interbred, an F2 generation is produced in this ratio:1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 whiteFurther crosses reveal that the dark-red and white F2 plants are true breeding. Based on the ratios in the F2 population, how many genes are involved in the production of color? How many additive alleles are needed to produce each possible phenotype? What are the possible genotypes that give rise to these phenotypes?
2 Dark-red: 4, AABB Med-dark:3, AABb AaBB med-red: 2, AAbb AaBb aaBB light-red: 1, aaBb Aabb white: 0, aabb
Assume that a recessive autosomal disorder occurs in 1 of 10,000 individuals (0.00001) in the general population and that in this population about 2 percent (0.02) of the individuals are carriers for the disorder. Compare this probability to the population at large.
2.50×10−3 Inbreeding increases the probability of this disorder.
In a population of 100 individuals, 49 percent are of the NN blood type. What percentage is expected to be MN assuming Hardy-Weinberg equilibrium conditions?
42 percent
Assume that in a Hardy-Weinberg population, 9% of the individuals are of the homozygous recessive phenotype. What percentage are homozygous dominant?
49%
Approximately, what percentage of cancers have an inherited component?
5-10%
Albinism is an autosomal recessive trait in humans. Assume that there are 100 albinos (aa) in a population of 1 million. How many individuals would be expected to be homozygous normal (AA) under equilibrium conditions?
980,100
How does the Ras protein transmit a signal from outside the cell into the cytoplasm?
Activated Ras proteins transduce a signal, which activates the transcription of genes that start cell division.
Which of the following factors is an example of a manmade carcinogen?
Air pollution
In an acute transforming retrovirus, what is v-onc?
An oncogene acquired from the host that can transform other infected host cells
Which of the following statements regarding heritability of cancer is true?
At least two mutational events are required for a cell to become cancerous.
Under normal conditions, when a cell needs to undergo apoptosis:
Bcl2 activity is inhibited.
The significance of checkpoints can be demonstrated by considering what happens when they are impaired. What would occur if there was a gain-of-function mutation in the promoter for the cyclin E gene such that cyclin E protein was always made at high levels even under conditions in which cyclin E would not normally be made?
Cells will pass through the G1/S checkpoint even if conditions are not ideal for cell division.
One of the Hardy-Weinberg assumptions states that all genotypes in the population are free of selective advantage. What influence might a selective advantage of a genotype have on a Hardy-Weinberg equilibrium?
Certain alleles will reach the next generation on a nonrandom basis, thus upsetting the equilibrium.
Cyclin D1-Cdk4 regulates entry into S phase through the following signal transduction pathway. Use this pathway to answer the questions below. Which conditions must be met before the cell can begin DNA replication? Select all that apply.
Cyclin D1 must be bound to cyclin dependent kinase (Cdk4). Cyclin D1 levels must be high The transcription factor, E2F, must be bound to DNA.
What findings led geneticists to postulate the multiple-factor hypothesis that invoked the idea of additive alleles to explain inheritance patterns?
Experimental results involving pigmentation in wheat showed that a number of additive alleles acting in Mendelian fashion could explain continuous variation.
In directional selection, both phenotypic extremes are equally selected against.
False
Mutations are regarded as a strong evolutionary mechanism for changing allelic frequencies.
False
What are the genetic consequences of inbreeding?
For a given allele, inbreeding increases the proportion of homozygotes in a population.
Which of the following statements about twins and twin studies is FALSE? See Section 21.4 (Page)
Fraternal twins are as close genetically to each other as are monozygotic twins
Most somatic cells in an adult organism are in which stage of the cell cycle?
G0
A number of mechanisms operate to maintain genetic diversity in a population. Why is such diversity favored?
Genetic diversity may better adapt a population to inevitable changes in the environment.
Under what circumstances do cells undergo apoptosis?
If DNA or chromosomal damage is so severe that its repair is impossible, the cell may initiate programmed cell death.
Which of the following statements best describes the relationship between the Hardy-Weinberg principle and the effects of natural selection?
If selection can be quantified, relative fitness values can be calculated and used to appropriately modify the Hardy-Weinberg equation.
Why does radiotherapy often have significant side effects?
In addition to killing cancer cells, radiotherapy can also kill normal cells too, causing side effects.
The Philadelphia chromosome is a translocation between chromosomes 22 and 9 that leads to translation of a BCR-ABL fusion protein. The normal ABL gene is a proto-oncogene that codes for a kinase involved in a cell signaling pathway. How does this chromosome abnormality lead to cancer?
In the fusion protein, the ABL protein is always active.
Compare this probability to the population at large.
Inbreeding increases the likelihood of homozygosity.
Given that TP53 is a recessive gene and is not located on the X chromosome, why would people who inherit just one mutant copy of a recessive tumor-suppressor gene be at higher risk of developing cancer than those without the recessive gene?
Individuals with two copies of the gene would need to experience separate mutations in both copies to develop cancer, whereas individuals with one functional copy would only need a single mutation.
How does activated p53 initiate apoptosis?
It activates the transcription of BAX and represses the transcription of Bcl2.
A recent study examining the mutation rates of 5669 mammalian genes (17,208 sequences) indicates that, contrary to popular belief, mutation rates among lineages with vastly different generation lengths and physiological attributes are remarkably constant (Kumar, S., and Subramanian, S. 2002. Proc. Natl. Acad. Sci. [USA] 99: 803-808). The average rate is estimated at What is the significance of this finding in terms of mammalian evolution?
It allows for broader interpretations of sequence comparisons. It provides for increased understanding of the mutational processes. It provides more credible estimates of divergence times of species.
Which of the following statements about inbreeding in a natural population is true? See Section 22.8 (Page) .
It can increase the frequency of homozygotes.
What happens in cases where the ras gene is mutated?
It continually signals cell division.
What is apoptosis?
It is a programmed cell death, a genetically controlled process that leads to the death of a cell.
What is the role of the p53 protein in the cell cycle in normal cells?
It temporarily arrests the cell cycle in G1 before entering S.
A woman inherited one mutant copy of the BRCA1 gene. When she was 40 years old, she developed breast cancer. In her breast tumor cells, both copies of the BRCA1 gene were mutated. This phenomenon is called:
Loss of heterozygosity
How is p53 activated?
MDM2 dissociates from p53 and p53 is phosphorylated and acetylated.
Some malignant breast cancer cells express higher than normal levels of the metalloproteinase gene MMP1. How does overexpression of MMP1 lead to malignancy?
Metalloproteinases digest components of the extracellular matrix, allowing cells to metastasize.
In general, mutations in genes that code for cell-adhesion molecules, cytoskeleton regulators, and proteolytic enzymes lead to which feature of malignant cancer cells?
Metastasis
Which of the following mutations would result in cancer?
Mutations that prevents the retinoblastoma protein (pRB) from binding to E2F transcription factor. Mutation that produces cyclin dependent kinases that are permanently active, regardless of cyclin levels.
What is the relationship between proto-oncogenes and oncogenes?
Oncogenes are mutant forms of proto-oncogenes.
What epigenetic changes have been found in cancer cells?
Overall, much less DNA methylation
How do we know that threshold traits are actually polygenic even though they may have as few as two discrete phenotypic classes?
Polygenic conditions involving thresholds occur if a range of expression is possible, but the trait is either expressed or not expressed. Environmental factors have a considerable impact on polygenic system, and therefore, on expression of threshold traits.
________ is a group of individuals belonging to the same species that live in a defined geographic area and actually or potentially interbreed.
Population
What are QTLs?
QTLs are quantitative trait loci and refer to genes controlling the expression of quantitative traits. Submit
In which ways could radiotherapy control or cure cancer?
Radiotherapy is often administered externally or internally to kill cancer cells by damaging their DNA.
In a cancer cell that has a ras oncogene:
Ras always has GTP bound.
Which of the following functions is typical for tumor suppressor genes?
Regulating cell cycle check points
One of the Hardy-Weinberg assumptions states that the population is infinitely large. What influence might a small population size have on the Hardy-Weinberg equilibrium?
Sampling error would cause random and possibly significant fluctuations in determination of gene frequencies.
Which of the following might explain why the level of cyclin B in a cell is not increasing heading into mitosis?
Spindle fibers are not properly formed. The attachment of spindle fibers to the kinetochores is inadequate.
What is a provirus?
The DNA copy of a retroviral genome that is inserted into the host genome
Which of the following statements describes metastasis?
The ability to form secondary tumors at another site
What must occur before a cell can pass the G1/S checkpoint?
The cell must be an adequate size and DNA damage must be repaired.
If there are two alleles of a gene controlling coat color in a population of mice and the frequency of the dominant allele is 0.3, which of the following must be true?
The frequency of the recessive allele is 0.7.
The percentage of heterozygous carriers can be calculated as 2×(p0.5)×(1−p0.5)×100. What must be assumed in order to use this formula?
The population must be in Hardy-Weinberg equilibrium.
Which of the following statements best describes the relationship between fitness and selection coefficient (s)?
The stronger the selection against a given genotype, the lower the fitness associated with that genotype.
Which of the following is NOT a characteristic of retroviruses?
They cause lysis of the host cell upon infection.
Given an inheritance pattern of incomplete dominance and 81 flowers that are red (R1R1), 18 flowers that are pink (R1R2), and 1 flower that is white (R2R2), the frequency of the R1 allele is 0.9.
True
Natural selection occurs when there is nonrandom elimination of genotypes from a population due to differences in viability or reproductive success.
True
Our environment contains both natural and human-made carcinogens.
True
Are there nucleotide substitutions that will not be detected by electrophoretic studies of a gene's protein product?
Yes, nucleotide substitutions may occur in non-coding regions of a gene. Yes, there are nucleotide substitutions that do not change the corresponding amino acid because the genetic code is degenerate. Yes, if an amino acid is replaced by another amino acid with similar properties, the change may not be detected by electrophoresis.
Cancer is:
a genetic disease caused by an accumulation of mutations in somatic cells.
Burkitt lymphoma is caused by a chromosome translocation. In an individual patient, all cancer cells have the same chromosome breakpoints; however, different patients have different chromosome breakpoints. This observation supports the idea that tumor cells:
arise from clonal expansion.
How do we assess environmental factors to determine if they impact the phenotype of a quantitatively inherited trait?
by heritability estimation
1. How do geneticists detect the presence of genetic variation as different alleles in a population? How do we know how much genetic variation is in a population? How do we know the age of the last common ancestor shared by two species? How do we know whether the genetic structure of a population is static or dynamic? How do we know when populations have diverged to the point that they form two different species?
by obtaining typical segregation patterns and have similarities in nucleotide and amino acid sequences by including responses to artificial selection and sequencing of nucleic acids and proteins by estimating time of divergence using various molecular clocks based on amino acid and/or nucleotide differences. by conducting assays of gene and/or genotypic frequencies over time and space by determining whether gene flow between populations becomes sufficiently reduced
What genetic changes take place during speciation?
chromosomal changes point mutations
All of the following are characteristics of genomic instability in cancer cells EXCEPT __________.
controlled cell division
The transition between G2 and M phase of the cell cycle happens when:
cyclin B and CDK1 are present and form an active complex.
How do we know that monozygotic twins are not identical genotypically as adults?
differences in inherited disease states
Passenger mutations in a tumor:
do not directly contribute to the cancer phenotype.
Heritability is a measure of the degree to which the phenotypic variation of a given trait is due to ________.
genetic factors
Prezygotic mechanisms
geographic seasonal behavioral mechanical physiological
postzygotic mechanisms
hybrid nonviability or weakness developmental hybrid sterility segregational hybrid sterility F2 breakdown
Which of the following circumstances might allow a lethal dominant allele to persist in a population?
incomplete penetrance late onset (lethality occurs after reproductive age) Submit
When are the major regulatory points in the cell cycle?
late G1 phase (G1/S checkpoint) late G2 phase (G2/M checkpoint) M phase (M checkpoint)
Predict the outcome of crossing a true-breeding medium-red plant and a white plant. What color(s) would you expect in the F1 offspring?
light-red
Which theory suggests that many factors or genes contribute to the phenotype in a cumulative or quantitative manner?
multiple factor hypothesis
Bell-shaped distributions produced by plotting results of F2 and F3 crosses are typical of which type of inheritance?
multiple-factor inheritance
All cells in a tumor:
originated from a common ancestor cell.
Migration occurs when individuals move between populations. Considering a single pair of alleles, A and a, what formula is used to indicate the new frequency of A in one generation of migration?
p i' = (1 - m)p i + mp m
An inbred strain of plants has a mean height of 24 cmcm. A second strain of the same species from a different geographical region also has a mean height of 24 cmcm. When plants from the two strains are crossed together, the F1F1 plants are the same height as the parent plants. However, the F2F2 generation shows a wide range of heights; the majority are like the P1P1 and F1F1 plants, but approximately 4 of 1000 are only 12 cmcm high, and about 4 of 1000 are 36 cmcm high. What mode of inheritance is occurring here?
polygenic 4 3cm
Radiation works as a cancer therapy because it:
preferentially causes damage to rapidly dividing cells.
Protein A is hormone-dependent transcription factor. A dominant mutation in protein A that causes activation of transcription without the presence of the hormone leads to activation of the cell cycle. The wild-type gene for protein A is an example of a/an:
proto-oncogene.
Which general term is used to group various biological and behavioral properties of organisms that act to prevent or reduce interbreeding?
reproductive isolating mechanisms
What is regarded as a strong evolutionary mechanism for changing allelic frequencies?
selection
Concordance refers to the frequency with which members of a twin pair express a ________ trait.
similar
In the case of complete dominance in a population in equilibrium, we cannot tell which individuals are homozygous dominants and which are heterozygous, what information is needed to determine the frequency of homozygous dominant and heterozygous genotypes?
the frequency of homozygous recessive genotype
Metastasis is:
the process of cells spreading and colonizing other parts of the body.
When a trait is polygenic, but has a small number of discrete classes, it is said to be a(n) ________ trait.
threshold
A benign tumor becomes a malignant tumor when the:
tumor has the ability to invade other tissues and form secondary tumors.
Genetic drift is primarily associated with what size breeding populations?
very small
In the following table, average differences of height, weight, and fingerprint ridge count between monozygotic twins (reared together and apart), dizygotic twins, and nontwin siblings are compared. TraitMZ Reared TogetherMZ Reared ApartDZ Reared TogetherSibs Reared TogetherHeight (cm)1.7 1.8 4.4 4.5 Weight (kg)1.9 4.5 4.5 4.7 Ridge count0.7 0.6 2.4 2.7 Based on the data in this table, which of these quantitative traits has the lowest heritability value?
weight
Predict the outcome of crossing two of the F1 plants from Part D. What color(s) would you expect in the offspring?
white, light-red, medium-red
