genetics exam 4
Given the following information, VG=15, VD=6, VI=2, VE=20, and VGE=0, what is the narrow-sense heritability of the trait in question?
0.2
Which of the following statements about histones and gene expression is correct?
Addition of methyl groups to the tails of histone proteins can lead to either activation or repression of transcription depending on which amino acid is modified.
Which of these scenarios is likely due to positive assortative mating?
Purebred dachshunds have a higher incidence of degenerative disc disease than mixed breed dogs.
Which of the following is necessary for natural selection to occur?
Variations of the trait must exist in the population.
operons are found only in
bacteria
The lac operon repressor . . .
binds to the operator sequence when lactose is unavailable.
siRNAs are produced by the
cleavage of double stranded RNA by Dicer enzyme
In twin studies, the heritability of a trait can be estimated by . .
doubling the difference in correlation coefficient between monozygotic and dizygotic twins.
In eukaryotic cells, genes that are coordinately activated by a particular stimulus __________.
-are often recognized by the same transcriptional activators. -may have short regulatory sequences in common in their promoters or enhancers.
Suppose that the frequency of a particular recessive condition in a population is 1/400 and that the population is at Hardy-Weinberg equilibrium. What is the frequency of heterozygotes in the population?
0.095
Suppose that phenotypic variation in the tail length of mice is summarized in the table below. Va=.3 Vd= .5 Vi= .1 Ve= .4 Vge=0 What is the narrow-sense heritability (h2) of tail length?
0.23
In a population of mice, there are two alleles of the A locus, A and a. Tests showed that, in this population, there are 173 mice of genotype AA, 423 Aa, and 258 aa. Calculate the frequency of the A allele.
0.45
A captive population of 120 flamingos has frequencies f(A)= .75 and f(a)= .25. 24 new flamingos are added to the group with frequencies f(A)= .55 and f(a)= .45. The frequency of A in the merged population is
0.717
An allele that is "fixed" in a population has a frequency of ___
1
A fish breeder wishes to increase the rate of growth in a stock by selecting for increased length at six weeks after hatching. The mean length of six-week-old fish in the population is currently 10 cm. Adult fish that had a mean length of 15 cm at six weeks of age were used to produce a new generation of young fish. If the narrow-sense heritability of the trait is 0.5, what is the expected mean length among the next generation of fish?
12.5 cm
A series of experiments shows that seed weight in a diploid grain is influenced by five genes with additive alleles A-E and non-additive alleles a-e. The highest-producing strain has seed heads weighing 40 grams and the lowest strain has 10-gram heads. By how much does the seed weight increase for each additive allele present in the genotype?
3 grams
operator sequence includes ____ end of promoter and ___ end of TSS in first gene
3'; 5'
How many genes are involved in controlling a quantitative trait if crossing two homozygotes on opposite ends of the phenotypic spectrum and then intercrossing the F1 results in F2 offspring that fall into 9 phenotypic classes?
4
A population of long-hair cats has a narrow-sense heritability value for fur length of h2 = 0.15. The aim is to breed cats with longer fur than the population currently exhibits. The current generation of cats has a mean fur length of 4 cm. The selected individuals that are bred for the next generation have a mean fur length of 6 cm. What is the expected average length of cat fur in the next generation?
4.3 cm
Three independently segregating genes with two alleles each, A/a, B/b, and C/c determine plant height additively in a population. The homozygote AABBCC is 66 cm tall and the homozygote aabbcc is 30 cm tall. How much does each additive allele contribute to the height of these plants?
6 cm
Based on the information in the previous question, if a plant has seed heads that weigh 28 grams, what might be its genotype?
AaBBCCDdee
If there is random mating in a population and no evolutionary forces are acting on the population, what will be the expected outcome?
Both the genotypic distribution and the allelic frequencies will remain the same
Three major epigenetic regulatory mechanisms include . . .
DNA methylation, covalent modification of histone tails, and RNA-based gene silencing.
Which of these phenomena does NOT involve epigenetic changes caused by environmental factors?
E.coli exposed to lactose turn on expression of lac operon genes
Which of the following is a correct statement regarding Angelman and Prader-Willi syndromes?
Individuals with Angelman and Prader-Willi display different phenotypes because they differ in which gene products are missing.
How does tryptophan function in the regulation of the trp operon?
It binds to the repressor and only then can this complex bind to DNA to prevent transcription of the operon
What is the role of glucose in lac operon regulation?
It decreases the amount of cAMP in the cell, preventing activation of lac operon expression above basal levels
Two neighboring Caribbean islands harbor iguana populations. One island (island A) has a total iguana population of 800, while the other (island B) has a population of 250. On island A, the frequency of an allele p is estimated at 0.75, while this same allele is present at a frequency of 0.90 on island B. If 100 iguanas migrate from island A to island B, what effect does this have on the frequency of allele p on island B?
It would decrease to 0.86.
The estimated broad-sense heritability for milk production in a herd of dairy cattle is high. Which of the following statements is a valid inference?
Little of the variation in milk production is due to environmental variation within the herd.
Consider a gene in mice that is normally maternally imprinted. If a deletion occurred in the gene, rendering it nonfunctional, what would be the expected phenotype in offspring heterozygous for the deletion?
Offspring that inherit the deletion from their mothers would be phenotypically normal, and those that inherit the deletion from their fathers would show the mutant phenotype associated with loss of the gene's function
How do promoters differ from enhancers?
Promoters must be located within a short distance upstream of the transcription start site, while enhancers may be located farther away or even downstream of the gene they regulate
When a population is in Hardy-Weinberg equilibrium for alleles A and a, which of the following will be true of the population?
The allele frequencies will remain constant from generation to generation. The genotypic frequencies can be predicted based on allele frequencies.
In the absence of tryptophan, what happens to the genes within the trp operon?
The repressor cannot bind to the operator in the absence of tryptophan, so the structural genes get transcribed.
What happens to the lac operon in the absence of lactose?
The repressor protein binds to the operator and prevents transcription of the structural genes
Is the following statement true or false? Epigenetics involves heritable, reversible modifications of DNA or histones that alter gene expression without changing the DNA sequence.
The statement is true.
If a chemical that inhibits histone deacetylation was injected into a mouse brain, which of the following would you expect to occur?
There would be a general increase in gene expression
How do epigenetic marks compare in monozygotic twins?
They are similar in early life but are increasingly dissimilar with age
Two highly inbred tobacco plants, one with dark green leaves and one with yellow leaves, are crossed with each other. The F1 offspring have light green leaves. Of 384 progeny from F1 × F1 crosses, 6 of them have dark green leaves and the rest show a continuous distribution of lighter colors ranging to yellow. What do these data suggest about the number of genes determining this trait?
Three genes control the trait.
How can expression of one gene result in several polypeptides with different amino acid sequences?
Through alternative sequencing of the pre mRNA
AQTLis ...
a chromosomal region containing a gene that influences a quantitative trait.
operons can be best defined as
a set of genes under common regulatory control
An animal breeder asks your advice about which of a number of traits could most effectively be selected for in his herd. Which would be the best choice?
a trait with high narrow-sense heritability
constitutive operon
always on
Quantitative traits . . .
are scored by measuring or counting
Operons ...
are transcribed to make a polycistronic mRNA that contains multiple protein-coding regions. are much more common in prokaryotes than in eukaryotes. often contain genes whose products function in the same biochemical pathway.
Cheetahs exhibit low genetic diversity and are thought to have experienced substantial reduction in population size at some point in their evolutionary history due to overhunting and loss of habitat that affected individuals at random, irrespective of their genotype. This is an example of
bottleneck effect
Which of the following types of eukaryotic gene regulation takes place at the level of DNA?
chromatin modification
beta- galactisudase
cleaves lactose into glucose and galactose
If a mutation in region 2 of the trp operon leader prevents the formation of the 2+3 antiterminator loop, what would be the effect?
constant attenuation of transcription even when tryptophan levels are low
Quantitative traits often exhibit a _____ phenotype distribution.
continuous
In a large population, which of the following is most likely to lead to fixation of a recessive allele?
directional selection
Additive alleles . . .
each contribute equally to the phenotype..
inducible and repressible systems can involve
either positive or negative control
A study from Sweden showed that individuals born in the early 1900's whose grandfathers experienced a food shortage during adolescence tended to live longer than those whose grandfathers had abundant food. The most likely explanation for this observation involves __________.
epigenetics
examples of constitutive operon
essential products (housekeeping genes), rRNA's, RNA polymerase
Zinc finger, leucine zipper and helix-turn-helix are
examples of DNA binding domains found in transcription factors
permease gene
facilitates entry of lactose into cell
Which term is given to the total genetic information carried by all members of a population?
gene pool
Polycistronic Expression
genes transcribed together
If individuals of one genotype respond to changes in the environment differently than individuals of another genotype, this demonstrates _______________ for that trait.
genotype-by-environment interaction
transacetylase gene
helps remove toxic biproducts
Which of these phrases is the most accurate and complete definition of the term "epigenome"
hertiable, reversible modifications to DNA or histones that control gene expression without altering DNA sequence
choose the FALSE statement
inbreeding leads to severe changes in allele frequencies
positive control
involves activators
negative control
involves repressors
Methylation of CpG islands . .
is associated with long-term inhibition of gene expression.
examples of inducible operon
lac, metabolic pathways (in presence of substrate, turn on enzymes)
___ of cytosine nucleotides in CpG islands in or near a gene's promoter results in reduced transcription of that gene
methylation
Which of the following increases genetic diversity within populations and decreases diversity between populations?
migration
Broad-sense heritability for a trait is 0.95. This indicates that . . .
most of the phenotypic variation seen for the trait is due to genetic differences between individuals.
An operon is controlled by a repressor. When the repressor binds to a small molecule, it binds to DNA near the operon. The operon is constitutively expressed if a mutation prevents the repressor from binding to the small molecule. The type of control illustrated is
negative repressible
are all genes expressed all the time?
no
Pairing between regions 3 and 4 of the trp operon leader sequence...
occurs when the tryptophan level inside the cell is high
activators and repressors bind to
operator
A group of individuals from the same species that can interbreed with one another is called a _____.
population
Oil content in sunflower seeds is controlled by five genes P-T, with each additive allele (designated by capital letters) adding 2% to the oil content above a baseline of 30% measured in plants with pp qq rr ss tt genotype. A plant of unknown genotype as an oil content of 46%. Which of the following is a possible genotype of that plant?
pp QQ RR SS TT
activator
promotes transcription
A new kind of tulip is produced that develops only purple or pink flowers. Assume that flower color is controlled by a single-gene locus, and that the purple allele (C) is dominant to the pink allele (c). A random sample of 1000 tulips from a large cultivated field yields 847 purple flowers, and 153 pink flowers. What is the frequency of the purple and pink alleles in this field population, assuming it is in Hardy-Weinberg equilibrium?
purple= 0.847, pink= 0.153
In terms of population genetics, an allele that becomes "fixed" . . .
q2
Which of the following does NOT lead to evolution of a population?
random mating
what can correspond to cell-type and/or disease state?
regulation, time and place, amount
repressor
represses transcription
when no lactose is present,
repressor binds to operator, negative control. no lac expression
lac operon
required for the breakdown of lactose as carbon source
Enhancers . . .
serve as binding sties for activator proteins.
operon
set of genes transcribed together, involved in same process
Individuals of a tree snake species vary from light to dark coloration. There are a greater proportion of snakes with a medium coloration after several generations. This change is most likely due to . . .
stabilizing selection
The relative fitness of each genotype in a population is shown below. These fitness values exemplify . . . AA Aa aa w= 0.8 0.8 1
the directional selection against completely dominant allele A
In the Hardy-Weinberg equation, 2pq represents the frequency of . . .
the heterozygous genotype
The probability that two alleles in an individual will be "identical by descent" because they were inherited from the same ancestor is estimated by . . .
the inbreeding coefficient.
Which of the following does NOT fit with Darwin's theory of evolution?
the number of individuals in a population will always be maintained at a label to minimize competition
Which of the following statements about regulation of gene expression is correct?
the regulation of gene expression is critical for the control of life processes in all organisms
The stability/half-life of eukaryotic mRNAs is influenced by elements located in _____________.
the untranslated regions of the mRNA
examples of repressible operon
trp operon, synthesis pathways
Chromatin remodeling complexes . . .
use energy from ATP to physically change the position of nucleosomes along a stretch of DNA.
inducible operon
usually off, only turned on when needed
repressible operon
usually on, can be turned off when no longer needed
Expression of the lac operon is highest . . .
when lactose is present and glucose is absent.
For a gene under negative repressible control, the presence of a small molecule . . .
would cause the gene's repressor to bind to DNA and inhibit transcription.
