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Name the individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With what organism did this person work?
A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?
What types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability?
The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus is called
In peas, gray seed color is dominant to white. For the purposes of this question, assume that Mendel crossed plants with gray seeds with each other and the following progeny were produced: 320 gray and 80 white.
(a) What is the most probable genotype of each parent?
(b) What genotypic and phenotypic ratios are expected in the progeny of such a cross?
(a) using the symbols G = gray and g = white, Gg X Gg
(b) genotypic = 1:2:1, phenotypic = 3:1
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child.
(a) What is the probability that their next child will be albino?
(b) What is the probability that their next child will be an albino girl?
(c) What is the probability that their next three children will be albino?
(b) 1/4 X 1/2 = 1/8
(c) 1/4 X 1/4 X 1/4 = 1/64
Under what conditions does one expect a 9:3:3:1 ratio?
dihybrid cross (F2) with independently assorting, completely dominant genes
How many different kinds of gametes will be expected by an individual with the genotype PpCcTTRr?
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child. What is the probability that their next child will be an albino girl?
1/4 X 1/2 = 1/8
Assuming independent assortment, what proportion of the offspring of the cross AaBbCcDd X AabbCCdd will have the aabbccdd genotype?
To test Mendel’s law of independent assortment, the experimenter needs a minimum of two different genes and their two alleles.
Assuming complete dominance, a 3:1 phenotypic ratio is expected from a monohybrid sib or self-cross.
A situation in which there are more than two alternative forms of a given gene is called ________.
A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.
Assume that a dihybrid cross (AaBb X AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. What phenotypic ratio would you expect from such a cross? Provide just the ratio, not the phenotypes.
(a) Diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse.
(b) What would be the expected phenotypic ratio in the progeny?
(a) AaBb X aabb
(b) 1 (agouti): 1 (black): 2 (albino)
The following F2 results occur from a typical dihybrid cross:
purple: A_B_ 9/16
white: aaB_ 3/16
white: A_bb 3/16
white: aabb 1/16
If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?
3 (white) :1 (purple)
What types of ratios are likely to occur in crosses (F2) when one is dealing with two interacting, epistatic gene pairs?
9:7, 9:3:4, 12:3:1, 15:1
females wild-type, males white-eyed
Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. What is the probability that their first son will have hemophilia?
Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose comb chicken is crossed with a walnut comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single.
(a) What are the probable genotypes of the parents?
(b) Give the genotypes of each of the offspring classes.
(a) Rrpp X RrPp
(b) R-Pp (walnut)
A particular cross gives a modified dihybrid ratio of 9:7. What phenotypic ratio would you expect in a testcross of the fully heterozygous F1 crossed with the fully recessive type? Diagram the testcross using A,a,B,b as symbol sets.
1:3 AaBb X aabb > AaBb, Aabb, aaBb, aabb
The enzyme glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive gene on the X chromosome in humans. A phenotypically normal woman (whose father had G6PD) is married to a normal man.
(a) What fraction of their sons would be expected to have G6PD?
(b) If the husband had G6PD, would it make a difference to your answer in part (a)?
A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild-type. Offspring of the F2 generation had the following phenotypes:
Sex Phenotype Number
male wild 96
male yellow 99
female wild 197
Based on this information:
(a) Is the mutant gene for yellow body behaving as a recessive or a dominant?
(b) Is the yellow locus on an autosome or on the X chromosome?
(a) recessive(b) X-linked
In a mating between individuals with the genotypes IAIB X IOIO, what percentage of the offspring are expected to have the O blood type?
Regarding the ABO blood group system in humans, if an individual is genetically IBIO and yet expresses the O blood type, it is likely that that individual has the _______ genotype.
A typical epistatic ratio is 9:3:4.
“Gain-of-function” mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype.
Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is recessive to its normal allele.
Name two forms of recombination in bacteria.
Bacteriophages engage in two interactive cycles with bacteria. What are these cycles?
lytic and lysogenic
Name the general category into which double-stranded circular extrachromosomal DNA elements such as F factors, ColE1, and R fall.
Jacob, Wollman, and others developed a linkage map of E. coli that is based on time. What form of recombination is involved in generating a linkage map based on time?
Conjugation: An Hfr bacterium conjugating with an F– strain allows one to generate a map that is dependent on the passage of the donor chromosome across a conjugation tube.
Distinguish between F+ and F– bacteria.
F+ bacteria contain an F factor or plasmid that is capable of initiating conjugation.
How does an auxotroph differ from a prototroph?
What are the roles of the recBCD genes?
In general, what two methods are used to grow bacteria in the laboratory?
Name three forms of recombination in bacteria.
conjugation, transformation, and transduction
Name the typical phases of the bacterial growth cycle in liquid culture medium.
lag, log (exponential), and stationary
Bacteria that are in a particular physiological state to become transformed are called ________.
Assume that one counted 67 plaques on a bacterial plate where 0.1 ml of a 10–5 dilution of phage was added to bacterial culture. What is the initial concentration of the undiluted phage?
67 X 105 X 10 = 6.7 X 107 pfu/ml (pfu = plaque-forming units)
What is meant by the term cotransformation?
What is a merozygote?
In a bacterial cross where the donor (Hfr) is a+b+ and the recipient strain (F–) is a–b–, it is expected that recombinant bacteria will all be a+b+.
Cotransduction of genes is an indication that the genes are linked.
Lysogeny is a process that occurs during transformation and conjugation.
When two genes fail to assort independently, the term normally applied is ________.
Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with the following circumstance:
Assume that, regarding a particular gene, one scored 30 second-division ascospore arrangements and 70 first-division arrangements in Neurospora. What would be the
map distance between the gene and the centromere?
The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila. Assume that a mahogany-eyed female was mated to an ebony-bodied male and that the resulting F1 phenotypically wild-type females were mated to mahogany, ebony males. Of 1000 offspring, what would be the expected phenotypes, and in what numbers would they be expected?
mahogany = 375;
ebony = 375;
wild-type = 125;
mahogany-ebony = 125.
Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism. If you examined 200 primary oocytes, in how many would you expect to see a chiasma between the two loci mentioned above?
Phenotypically wild-type F1 female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles, produced the following offspring when crossed to homozygous light-straw males:
Compute the map distance between the light and straw loci.
Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males, and the following phenotypes were observed:
smooth abdomen, straw body 820 Lobe 780
smooth abdomen, Lobe 42
straw body 58
smooth abdomen 148
Lobe, straw body 152
(a) Give the gene order and map units between these three loci.
(b) What is the coefficient of coincidence?
(a) Lobe is in the middle.
smooth abdomen---5---Lobe-----------15-------------straw body
In Drosophila, assume that the gene for scute bristles (s) is located at map position 0.0 and that the gene for ruby eyes (r) is at position 15.0. Both genes are located on the X chromosome and are recessive to their wild-type alleles. A cross is made between scute-bristled females and ruby-eyed males. Phenotypically wild-type F1 females were then mated to homozygous double mutant males, and 1000 offspring were produced. Give the phenotypes and frequencies expected.
Answer: scute = 425; ruby = 425; wild-type = 75; scute-ruby = 75
To what scientific activities do the terms synkaryon and heterokaryon refer?
cell (heterokaryon) and nuclear (synkaryon) fusion and gene mapping in eukaryotes
a) In a three-point mapping experiment, what three general classes of offspring are expected (assuming crossovers occur)? (b) How many different genotypic classes are expected?
(a) Noncrossovers, single crossovers, double crossovers
What is the expected evolutionary significance of genetic recombination?
production of genetic variation
Two lines of work indicated that crossing over actually involves breakage and reunion of chromatid material. What organisms were involved, and who did the work?
Creighton and McClintock (corn) and Stern (Drosophila)
In the early 1900s, two scientists noted that there were many more genes than chromosome pairs, thus setting the stage for the suggestion that some gene loci might be linked during meiotic processes. Who were these two scientists?
What is the relationship between the degree of crossing over and the distance between two genes?
base, sugar, and phosphate.
Reverse transcriptase is an enzyme found in association with retroviral activity. It has the property of
What are the two major components of the Tobacco Mosaic Virus?
In the classic experiment conducted by Hershey and Chase, why was the pellet radioactive in the centrifuge tube that contained bacteria with viruses, which had been grown on medium containing 32P?
If 15 percent of the nitrogenous bases in a sample of DNA from a particular organism is thymine, what percentage should be cytosine?
In an analysis of the nucleotide composition of double-stranded DNA to see which bases are equivalent in concentration, which of the following would be true?
A + C = G + T
If the GC content of a DNA molecule is 60 percent, what are the molar percentages of the four bases (G, C, T, A)?
(a) Assume that A + T/G + C equals 0.5 in one strand of DNA. What is the ratio of these bases in the complementary strand? (b) If A + G/T + C equals 0.5 in one strand, what is the ratio of these bases in the complementary strand?
At what approximate wavelengths do DNA, RNA, and proteins maximally absorb light?
ribose in RNA, deoxyribose in DNA; uracil in RNA replaces thymine in DNA
left-handed helix with two antiparallel complementary strands, 1.8 nm in diameter, 12 bases per turn, zigzag configuration, and shallow major groove
During the polymerization of nucleic acids, covalent bonds are formed between neighboring nucleotides. Which carbons are involved in such bonds?
C-3' and C-5'
G and C are present in both DNA and RNA.
Hershey and Chase used labeled DNA and protein to determine that DNA is the genetic material in bacteria.
Avery et al. (1944) determined that DNA is the genetic material in bacteriophage.
In 1953, Watson and Crick published a paper that described the structure of DNA.
In E. coli, which terms accurately reflect the nature of replication of the chromosome?
Structures located at the ends of eukaryotic chromosomes are called
The discontinuous aspect of replication of DNA in vivo is caused by
During DNA replication, what is the function of RNA primase?
RNA primase provides a free 3'-OH upon which DNA polymerization depends.
What primary ingredients, coupled with DNA polymerase I, are needed for the in vitro synthesis of DNA?
dNTP, DNA template, primer DNA or RNA, Mg2+ (appropriate buffering, temperature, and salt concentrations might be considered “secondary” ingredients)
DNA replicates conservatively, which means that one of the two daughter double helices is “old” and the other is “new.”
DNA strand replication begins with an RNA primer.
A nucleosome is a structure associated with the nuclear membrane. It helps maintain a stable relationship between the extracellular matrix and the membrane itself.
A characteristic of aging cells is that their telomeres become shorter.
Viral chromosomes exist in a variety of structures and can be made up of the following:
In E. coli, the genetic material is composed of
In human chromosomes, there are satellite DNA sequences of about 170 base pairs in length that are present in tandem arrays of up to 1 million base pairs. Found mainly in centromere regions, they are called
In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exists. What is it called and what types of elements are involved?
Chromatin of eukaryotes is organized into repeating interactions with protein octamers called nucleosomes. Nucleosomes are composed of which class of molecules?
What is unusual about the amino acid composition of histones? How is the function of histones related to the amino acid composition? Of which histones are nucleosomes composed?
A particular variant of the lambda bacteriophage has a double-stranded DNA genome of 51,365 base pairs. How long, in units of length measurement, would this DNA be?
What is an intron and what is the relationship between an intron and heterogeneous nuclear
An intron is a section of DNA, which, when transcribed as part of an RNA, is eventually spliced out of that RNA. The entire initial gene transcript, which may serve as an eventual mRNA (after intron removal and other forms of processing), is called heterogeneous nuclear RNA.
What are minisatellites and microsatellites?
Both are highly repetitive, relatively short DNA sequences. Microsatellites have a shorter repeat length than do minisatellites.
Describe the chromosomal conformations of fX174 and polyoma viruses.
single-stranded DNA, circular and double-stranded DNA, circular, respectively
Discuss the possible origin of mitochondria and chloroplasts.
development of endosymbionic relationships between primitive, free-living bacteria-like organisms
Describe the method of replication of mtDNA.
List nuclear-encoded gene products that are essential to the biological activity of mitochondria.
DNA and RNA polymerases, initiation and elongation factors required for translation, ribosomal proteins, aminoacyl tRNA synthetases, and some RNAs
The size of chloroplast DNA is much greater than mitochondrial DNA. What accounts for the difference in size?
cpDNA has many noncoding sequences, both within and between genes. In addition, cpDNA contains a larger number of genes.
The E. coli chromosome is circular, double-stranded DNA.
Each human contains an identical set of VNTRs.
Nutritional mutations can be defined as
. those mutations that do not allow an organism to grow on minimal medium, but do allow the organism to grow on complete medium.
Two formal terms used to describe categories of mutational nucleotide substitutions in DNA are
transversions and transitions.
Name two mutagens that are classified as base analogues.
5-bromouracil and 2-aminopurine
A class of mutations that results in multiple contiguous amino acid changes in proteins is likely to be the following:
Ultraviolet light causes pyrimidine dimers to form in DNA. Some individuals are genetically incapable of repairing some dimers at “normal” rates. Such individuals are likely to suffer from
Three human disorders—fragile-X syndrome, myotonic dystrophy, and Huntington disease— are conceptually linked by a common mode of molecular upset. Describe the phenomena that link these disorders.
What is meant by the term photoreactivation repair?
Regarding the nature of the ABO blood groups, what condition leads to the O blood type?
failure to modify the H substance due to lack of glycosyltransferase activity
What is the common influence of ultraviolet light on DNA?
One type of mutation involves the replacement of a purine with a purine, while another causes the replacement of a pyrimidine with a purine. What general terms are associated with these two mutational phenomena?
The shorter the wavelength of a radiation source, the greater its likelihood of causing damage.
When using the attached-X method of mutation assessment in Drosophila, sons inherit their X chromosome from their mother and their Y chromosome from their father.
Strand discrimination during the process of DNA repair is based on DNA methylation in E. coli.
When considering the initiation of transcription, one often finds consensus sequences located in the region of the DNA where RNA polymerase(s) bind. Which are common consensus sequences?
What is the name given to the three bases in a messenger RNA that bind to the anticodon of tRNA to specify an amino acid placement in a protein?
An intron is a section of
Which of the following sets of two terms relates most closely to split genes?
Significant in the deciphering of the genetic code was the discovery of the enzyme polynucleotide phosphorylase. What was this enzyme used for?
The genetic code is said to be triplet, meaning that
Introns are known to contain termination codons (UAA, UGA, or UAG), yet these codons do not interrupt the coding of a particular protein. Why?
Introns are removed from mRNA before translation.
What is polycistronic mRNA?
Polycistronic mRNA is seen primarily among prokaryotes where one mRNA carries coding information and internal punctuation for the translation of more than one protein.
What two experimental procedures allowed deciphering of the ordered triplet assignments of the genetic code?
The enzyme polynucleotide phosphorylase is capable of generating a random assembly of ribonucleotides.
A 3'-poly-A tail and a 5'-cap are common components of prokaryotic RNAs.
Which of the following are among the major components of prokaryotic ribosomes?
A. 12S rRNA, 5.8S rRNA, and proteins
B. 16S rRNA, 5.8S rRNA, and 28S rRNA
C. 16S rRNA, 5S rRNA, and 23S rRNA
D. lipids and carbohydrates
E. 18S rRNA, 5.8S rRNA, and proteins
The one-gene:one-enzyme hypothesis emerged from work on which two organisms?
One form of posttranslational modification of a protein includes
Side groups of amino acids are typically grouped under which of the following categories?
A protein is 300 amino acids long. Which of the following is the minimum number of nucleotides in the section of DNA that codes for this protein? (Remember, DNA is double-stranded.)
5’-AUGGUGCUGAAG : methionine-valine-leucine-lysine
Assume that a mutation in the DNA occurs so that the fourth base (counting from the 5’ end) of the messenger RNA now reads A rather than G. What sequence of amino acids will the mRNA now code for? (You do not need a copy of the genetic code to answer the question.)
The discovery of RNA self-splicing in Tetrahymena by T. Cech (1982) and others revealed that RNA can demonstrate autonomous catalytic properties. What are RNAs that undergo such splicing often called?
Early in the 1900s, Sir Archibald Garrod studied a number of metabolic defects in humans. One particular disorder involved the inability to metabolize homogentisic acid. What is the name of this disorder?
Using the standard set of 20 amino acids, how many different polypeptides with a length of 250 amino acids, each with a unique sequence, could be formed?
The ribonucleic acid components known to exist in eukaryotic ribosomes are the following: 5.8S, 18S, 28S, and 5S.
rDNA is the portion of a genome that is involved in the production of ribosomal RNA.
Catabolism is the degradation of large molecules into smaller, simpler ones, while anabolism is a synthetic phase of metabolism that often ends up generating macromolecules.
What term refers to a contiguous genetic complex that is under coordinated control?
Inthe lac operon, the product of structural gene lacZ is capable of
splittingthe β-linkage of lactose
Regarding eukaryotic and prokaryotic genetic regulation, what process seems to be the most similar between the two?
A constitutive mutation in the lac operon may be of several types. Name two types of constitutive mutation.
The catabolite repression system in E. coli essentially represses the lac operon when glucose is present. What evolutionary advantage would favor evolution of such a system?
Describe the function and general nature of promoters in eukaryotes.
What is the term that refers to the regulatory events that establish a specific pattern of gene activity and developmental fate for a given cell?
D. gradient regulated
How does determination relate to differentiation?
How does determination relate to differentiation?
Define the following terms:
a) determination: the early commitment of a cell to an eventual developmental fate
(b) differentiation: the set of functional and structural changes associated with the expression of that developmental fate
Mutations in the selector genes sometimes form structures in the wrong segment, transforming the antenna of a fly into a leg, for example. What term is given to such mutations?
Segmentation genes, such as the pair-rule class, are inherited through mitochondrial DNA in Drosophila.
A homeobox gene is one that produces a group of repetitive base sequences such as a VNTR.
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