There is one DNA molecule per chromosome
If eukaryotic cells are broken and the contents of their nuclei are examined under the electron microscope, each chromosome appears as a mass of spaghetti-like fibers with a diameter of about 30 nm. An example is shown in the electron micrograph in Figure 3-9. In the 1960s, Ernest DuPraw studied such chromosomes carefully and found that there are no ends protruding from the fibrillar mass. This finding suggests that each chromosome is one, long, fine fiber folded up in some way. If the fiber...
Positioneffect variegation in Drosophila
An interesting genetic phenomenon first discovered in Drosophila revealed that epigenetic signals are able to spread from one chromosomal region to adjacent DNA. In these experiments, flies were irradiated with X rays to induce mutations in their germ cells. The progeny of the irradiated flies were screened for unusual phenotypes. A mutation in the white gene, near the tip of the X chromosome, will result in progeny with white eyes instead of the wild-type red color. Some of the progeny had...
Info Hbc
Figure 18-14 The bcd anteriorless mutant phenotype can be rescued by wild-type cytoplasm or purified bcd mRNA. a In embryos derived from bcd mothers, the anterior head and thoracic segments do not form, producing the anteriorless phenotype. b If anterior cytoplasm from an early wild-type donor embryo is injected into the anterior of a recipient embryo derived from a bcd mutant mother, a fully normal embryo and larva are produced. Cytoplasm from any other part of the donor embryo does not...
Info Shd
43. Every Friday night, genetics student Jean Allele, exhausted by her studies, goes to the student union's bowling lane to relax. But even there, she is haunted by her genetic studies. The rather modest bowling lane has only four bowling balls two red and two blue. They are bowled at the pins and are then collected and returned down the chute in random order, coming to rest at the end stop. Over the evening, Jean notices familiar patterns of the four balls as they come to rest at the stop....
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Figure 9-17 Translation initiation in prokaryotes. Initiation factors assist the assembly of the ribosome at the translation start site and then dissociate before translation. After J. Berg, J. Tymoczko, and L. Stryer, Biochemistry, 5th ed. Copyright 2002 by W. H. Freeman and Company. Figure 9-17 Translation initiation in prokaryotes. Initiation factors assist the assembly of the ribosome at the translation start site and then dissociate before translation. After J. Berg, J. Tymoczko, and L....
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Figure 4-8 Recombination between unlinked genes by independent assortment. This diagram shows two chromosome pairs of a diploid organism with A and a on one pair and B and b on the other. Independent assortment produces a recombinant frequency of 50 percent. Note that we could represent the haploid situation by removing the parental P cross and the testcross. Figure 4-8 Recombination between unlinked genes by independent assortment. This diagram shows two chromosome pairs of a diploid organism...
P1
a. It is possible to move these cells around during development. When the positions of ABa and ABp are physically interchanged, the cells develop according to their new position. In other words, the cell that was originally in the ABa position now gives rise to one body-wall muscle cell, whereas the cell that was originally in the ABp position now gives rise to three pharyngeal muscle cells. What does that tell us about the developmental processes controlling the fates of ABa and ABp b. If EMS...
Gtac
Figure 11-19 Printout from an automatic sequencer that uses fluorescent dyes. Each of the four colors represents a different base. N represents a base that cannot be assigned, because peaks are too low. Note that, if this were a gel as in Figure 11-18c, each of these peaks would correspond to one of the dark bands on the gel in other words, these colored peaks represent a different readout of the same sort of data as are produced on a sequencing gel. Figure 11-19 Printout from an automatic...
The Genetics Of Bacteria And Their Viruses
Sexual union of bacteria. Cells of Escherichia coli that have become attached by pili prior to DNA transfer between donor and recipient cell types. Dr. L. Caro Science Photo Library Photo Researchers. Sexual union of bacteria. Cells of Escherichia coli that have become attached by pili prior to DNA transfer between donor and recipient cell types. Dr. L. Caro Science Photo Library Photo Researchers.
Evidence from cytology
How did the chromosome theory take shape Evidence accumulated from a variety of sources. One of the first lines of evidence came from observations of how chromosomes behave during the division of a cell's nucleus. Mendel's results lay unnoticed in the scientific literature until 1900, when they were repeated independently by other researchers. In the late 1800s, biologists were keenly interested in heredity, even though they were unaware of Mendel's work. One key issue of that era was the...
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Figure 15-6 The use of colchicine to generate a tetraploid from a diploid. Colchicine added to mitotic cells during metaphase and anaphase disrupts spindle-fiber formation, preventing the migration of chromatids after the centromere is split. A single cell is created that contains pairs of identical chromosomes that are homozygous at all loci. Figure 15-6 The use of colchicine to generate a tetraploid from a diploid. Colchicine added to mitotic cells during metaphase and anaphase disrupts...
S24
Figure 10-30 X inactivation produces the coat pattern of a calico cat. a A calico cat. b Calico cats are females heterozygous for the alleles O which causes fur to be orange and o which causes it to be black . Inactivation of the O-bearing X chromosome produces a black patch expressing o, and inactivation of the o-bearing X chromosome produces an orange patch expressing O. The white areas are caused by a separate genetic determinant present in calicos. Part a by Anthony Griffiths. Figure 10-30...
Deviations from independent assortment
In the early 1900s, William Bateson and R. C. Punnett were studying inheritance of two genes in the sweet pea. In a standard self of a dihybrid F1, the F2 did not show the 9 3 3 1 ratio predicted by the principle of independent assortment. In fact Bateson and Punnett noted that certain combinations of alleles showed up more often than expected, almost as though they were physically attached in some way. They had no explanation for this discovery. Later, Thomas Hunt Morgan found a similar...
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Figure 11-9 Structure of a bacterial artificial chromosome BAC , used for cloning large fragments of donor DNA. CMP- is a selectable marker for chloramphenicol resistance. oriS, repE, parA, and parBare F genes for replication and regulation of copy number. cosN is the cos site from X phage. Hindlll and BamHI are cloning sites at which donor DNA is inserted. The two promoters are for transcribing the inserted fragment. The NotI sites are used for cutting out the inserted fragment. Figure 11-9...
O Qci
Ribosome structure. This image shows at atomic resolution a surface of the ribosome from the bacteria Haloarcula marismortui, deduced from X-ray crystallography. The portion of the ribosome consisting of RNA is shown in blue that consisting of protein is shown in purple. The white, red, and yellow structures in the center are tRNAs at the E, P, and A binding sites, their acceptor stems disappearing into a cleft in the ribosome. From P. Nissen, J. Hansen, N. Ban, P. B. Moore, and T. A. Steitz,...
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27. Devise imaginative screening procedures for detecting the following b. Mutants lacking flagella in a haploid unicellular alga c. Supercolossal-size mutants in bacteria d. Mutants that overproduce the black compound melanin in normally white haploid fungus cultures e. Individual humans in large populations whose eyes polarize incoming light f. Negatively phototrophic Drosophila or unicellular algae g. UV-sensitive mutants in haploid yeast 28. A man and a woman with no record of genetic...
Solved Problems Ikr
1. The anterior determinant in the Drosophila egg is bcd. A mother heterozygous for a bcd deletion has only one copy of the bcd gene. With the use of P elements to insert copies of the cloned bcd gene into the genome by transformation, it is possible to produce mothers with extra copies of the gene. Shortly after the blastoderm has formed, the Drosophila embryo develops an indentation called the cephalic furrow that is more or less perpendicular to the longitudinal body axis. In the progeny of...
Caf1
Figure 7-20 Assembling nucleosomes during DNA replication. The protein CAF-1 brings histones to the replication fork, where they are assembled to form nucleosomes. For simplicity, nucleosome assembly is shown on only one of the replicated DNA molecules. Figure 7-20 Assembling nucleosomes during DNA replication. The protein CAF-1 brings histones to the replication fork, where they are assembled to form nucleosomes. For simplicity, nucleosome assembly is shown on only one of the replicated DNA...
Finding Specific Clones By Using Probes A
library might contain as many as hundreds of thousands of cloned fragments. This huge collection of fragments must be screened to find the recombinant DNA molecule containing the gene of interest to a researcher. Such screening is accomplished by using a specific probe that will find and mark only the desired clone. There are two types of probes those that recognize a specific nucleic acid sequence and those that recognize a specific protein. Probes for finding DNA Probing for DNA makes use of...
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is already externally divided into 14 segments from anterior to posterior 3 head, 3 thoracic, and 8 abdominal segments Figure 18-21b . By this time, each segment has developed a unique set of anatomical structures, corresponding to its special identity and role in the biology of the animal. At the end of 12 hours, distinct organs first form. At 15 hours, the exoskeleton of the larva begins to form, with its specialized hairs and other external structures. Only 24 hours after development began...
Discovery of the fertility factor F
In 1953, William Hayes discovered that in the above types of crosses the conjugating parents acted unequally later we shall see ways to demonstrate this . It seemed that one parent and only that parent transferred some of or all its genome into another cell. Hence one cell acts as donor, and the other cell as a recipient. This is quite different from eukaryotic crosses in which parents contribute nuclear genomes equally. MESSAGE The transfer of genetic material in E. coli conjugation is not...
Info Dpr
Note Py any pyrimidine Pu any purine. A circular bacterial plasmid pBP1 has a single HindIII restriction-enzyme site in the middle of a tetracycline-resistance gene ieiR . Fruit fly genomic DNA is digested with HindIII, and a library is made in the plasmid vector pBP1. Probing reveals that clone 15 contains a specific Drosophila gene of interest. Clone 15 is studied by restriction analysis with HindIII and another restriction enzyme, EcoRV. The ethidium bromide-stained electrophoretic gel...
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A plant from a standard stock that is homozygous for all five recessive alleles is crossed to a wild-type plant from Mexico that is homozygous for all five dominant alleles. The F1 plants express all the dominant alleles and, when backcrossed to the recessive parent, give the following progeny phenotypes colored, green, starchy, smooth, tall 360 white, bronze, waxy, shrunk, dwarf 355 colored, bronze, waxy, shrunk, dwarf 40 white, green, starchy, smooth, tall 46 colored, green, starchy, smooth,...
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b. What is the ratio of normal-leaved to potato-leaved plants when you assume that p is not located on chromosome 6 39. A tomato geneticist attempts to assign five recessive genes to specific chromosomes by using trisomics. She crosses each homozygous mutant 2n to each of three trisomics, involving chromosomes 1, 7, and 10. From these crosses, the geneticist selects trisomic progeny which are less vigorous and backcrosses them to the appropriate homozygous recessive. The diploid progeny from...
The Following Corn Loci Are On One Arm Of Chromosome 9 In The Order Indicated
a. Provide a genetic hypothesis that explains the three sets of testcross results. b. Draw the key chromosomal features of meiosis in the F1 from a cross of the Californian and Chilean lines. 42. An aberrant corn plant gives the following RF values when testcrossed The locus order is centromere-d-f-b-x-y-p. The aberrant plant is a healthy plant, but it produces far fewer normal ovules and pollen than the control plant. a. Propose a hypothesis to account for the abnormal recombination values and...
Sequencing a simple genome by using the whole genome shotgun approach
The logic of whole genome shotgun WGS sequencing is sequence first, map later. First, sequence reads are obtained from clones randomly selected from a whole genome library without any information on where these clones map in the genome. Such a library is called a shotgun library. Then, these sequence reads are assembled into a consensus sequence covering the whole genome by matching homologous sequences shared by reads from overlapping clones. Bacterial DNA is essentially single-copy DNA, with...
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a. What is the name given to the type of gene interaction in this example b. What are the genotypes of the individuals in the pedigree If there are alternative possibilities, state them. 56. A researcher crosses two white-flowered lines of Antirrhinum plants as follows and obtains the following results a. Deduce the inheritance of these phenotypes, using clearly defined gene symbols. Give the genotypes of the parents, F1, and F2. b. Predict the outcome of crosses of the F1 to each parental...
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a. Define your own symbols and show genotypes of all four pure lines. b. Show how the FJ phenotypes and the F2 ratios are produced. c. Show a biochemical pathway that explains the genetic results, indicating which gene controls which enzyme. 60. In common wheat, Triticum aestivum, kernel color is determined by multiply duplicated genes, each with an R and an r allele. Any number of R alleles will give red, and the complete lack of R alleles will give the white phenotype. In one cross between a...
I Cqk
Figure 11-38 Gene therapy in mice. a The rat growth-hormone gene RGH , under the control of a mouse promoter region that is responsive to heavy metals, is inserted into a plasmid and used to produce a transgenic mouse. RGH compensates for the inherent dwarfism lit lit in the mouse. RGH is inherited in a Mendelian dominant pattern in the ensuing mouse pedigree. b Transgenic mouse. The mice are siblings, but the mouse on the left was derived from an egg transformed by injection with a new gene...
Info Oll
Amino acids incorporated into protein b. Label the 5' and 3' ends of DNA and RNA, as well as the amino and carboxyl ends of protein. 2. Consider the following segment of DNA Assume that the top strand is the template strand used by RNA polymerase. c. Draw the corresponding amino acid chain. d. Label its amino and carboxyl ends. Repeat, assuming the bottom strand to be the template strand. 3. A mutational event inserts an extra nucleotide pair into DNA. Which of the following outcomes do you...
Problems Tvf
1. One way to look for auxotrophic mutants in microbes is to inoculate thousands of mutagenized colonies in specific positions on plates of fully supplemented medium, then to use a pad of sterile felt to transfer cells from these colonies into similar positions on plates of minimal medium replica-plating . Auxotrophs do not grow on minimal medium. Would you call this a selection or a screen for auxotrophs Explain. 2. You wish to find mutants of the haploid alga Chlamy-domonas that are defective...
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Corncobs Only about half as many seeds as usual a. What key features of the data are different from the expected results b. State a concise hypothesis that explains the results. c. Show genotypes of parents and progeny. d. Draw a diagram showing the arrangement of al-leles on the chromosomes. e. Explain the origin of the two classes of progeny having three and five members. 1. What do a gene for tassel length and a gene for rust resistance mean 2. Does it matter that the precise meaning of the...
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a. Deduce the inheritance of these coat colors and use gene symbols of your own choosing. Show all parent and progeny genotypes. b. If the black animals in crosses 7 and 8 are crossed, what progeny proportions can you predict by using your model 12. In a maternity ward, four babies become accidentally mixed up. The ABO types of the four babies are known to be O, A, B, and AB. The ABO types of the four sets of parents are determined. Indicate which baby belongs to each set of parents a AB X O, b...
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2. If the GC content of a DNA molecule is 56 percent, what are the percentages of the four bases A, T, G, and C in this molecule If the GC content is 56 percent, then, because G C, the content of G is 28 percent and the content of C is 28 percent. The content of AT is 100 56 44 percent. Because A T, the content of A is 22 percent and the content of T is 22 percent. 3. Describe the expected pattern of bands in a CsCl gradient for conservative replication in the Meselson-Stahl experiment. Draw a...
Ecv K
Figure 15-26 Pseudolinkage of genes due to translocation. When a translocated fragment carries a marker gene, this marker can show linkage to genes on the other chromosome. Figure 15-26 Pseudolinkage of genes due to translocation. When a translocated fragment carries a marker gene, this marker can show linkage to genes on the other chromosome. that were originally on different chromosomes. Apparent linkage of genes known normally to be on separate nonhomologous chromosomes sometimes called...
Imprinting
Another example of epigenetic inheritance is parental imprinting, discovered about 15 years ago in mammals. In parental imprinting, certain autosomal genes have seemingly unusual inheritance patterns. For example, the mouse igf2 gene is expressed in a mouse only if it was inherited from the mouse's father. This is an example of maternal imprinting because a copy of the gene derived from the mother is inactive. Conversely, the mouse H19 gene is expressed only if it was inherited from the mother...
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Figure 21-2 Changes in shell size and curvature in the bivalve mollusc Gryphaea in the course of its phyletic evolution in the early Jurassic. Only the left shell is shown. In each case, the shell back and a longitudinal section through it are illustrated. After A. Hallam, Morphology, Palaeoecology and Evolution of the Genus Gryphaea in the British Lias, Philosophical Transactions of the Royal Society of London Series B 254, 1968, 124. principles governing changes in the genetic composition of...
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Microscopic ascospores are dissected and transferred one by one to culture tubes Crossed with wild type of opposite mating type Microscopic ascospores are dissected and transferred one by one to culture tubes Hundreds of tubes of complete medium are inoculated with single ascospores Conidia asexual spores from each culture are then tested on minimal medium Conidia from the cultures that fail to grow on minimal medium are then tested on a variety of supplemented media No growth on minimal medium...
Classes of tumorsuppressor genes
The normal functions of tumor-suppressor genes fall into categories complementary to those of proto-oncogenes see Table 17-1 . Some tumor-suppressor genes encode negative regulators of the cell cycle, such as the Rb protein or elements of the TGF-p signaling pathway. Others encode positive regulators of apop-tosis at least part of the function of p53 falls into this category . Still others are indirect players in cancer, with a normal role in the repair of damaged DNA or in controlling cellular...
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a. Are these two abnormalities caused by the same gene or separate genes State your reasons clearly. b. Is the gene or genes autosomal or sex-linked c. Does the pedigree show any evidence of incomplete penetrance or expressivity If so, make the best calculations that you can of these measures. 63. Workers of the honeybee line known as Brown nothing to do with color show what is called hygienic behavior that is, they uncap hive compartments containing dead pupae and then remove the dead pupae....
Using the Ordered Clone Approach to Sequence a Complex Genome
The logic of ordered clone sequencing is the opposite of that for the whole genome shotgun approach map first, sequence later. Individual cloned inserts from a genomic library are screened to look for similarities in restriction-enzyme recognition sites, indicating that two inserts are contiguous in the genome. This results in a set of ordered and oriented clones that together span the genome. Such an ordered and oriented set of clones covering the whole genome is called the physical map of the...
Use of suppressors to demonstrate a triplet code
Convincing proof that a codon is, in fact, three letters long and no more than three came from beautiful genetic experiments first reported in 1961 by Francis Crick, Sidney Brenner, and their co-workers. These experiments used mutants in the rll locus of T4 phage. The use of rll mutations in recombination analysis was discussed in Chapter 5. Phage T4 is usually able to grow on two different E. coli strains, called B and K. However, mutations in the rll gene change the host range of the phage...
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Prophase I Leptotene. The chromosomes become visible as long, thin single threads. The process of chromosome contraction continues in leptotene and throughout the entire prophase. Small areas of thickening chromomeres develop along each chromosome, which give it the appearance of a necklace of beads. Prophase I Zygotene. Active pairing of the threads makes it apparent that the chromosome complement of the meiocyte is in fact two complete chromosome sets. Thus, each chromosome has a pairing...
Problems Qfu
1. Describe the state of the F factor in an Hfr, F , and F strain. 2. How does a culture of F cells transfer markers from the host chromosome to a recipient 3. With respect to gene transfer and integration of the transferred gene into the recipient genome compare the following a. Hfr crosses by conjugation and generalized transduction. b. F' derivatives such as F' lac and specialized trans-duction. 4. Why is generalized transduction able to transfer any gene, but specialized transduction is...
Inbreeding and assortative mating
Random mating with respect to a locus is common within populations, but it is not universal. Two kinds of deviation from random mating must be distinguished. First, individuals may mate with others with whom they share some degree of common ancestry, that is, some degree of genetic relationship. If mating between relatives occurs more commonly than would occur by pure chance, then the population is inbreeding. If mating between relatives is less common than would occur by chance, then the...
The DNA structure
Even before the structure of DNA was elucidated, genetic studies indicated that the hereditary material 1. Because essentially every cell in the body of an organism has the same genetic makeup, it is crucial that the genetic material be faithfully replicated at every cell division. Thus the structural features of DNA must allow faithful replication. These structural features will be considered later in this chapter. 2. Because it must encode the constellation of proteins expressed by an...
Acridine Orange Is An Effective Mutagen For Producing Null Alleles By Mutation.
1. Consider the wild-type and mutant sequences below Wild CTTGCAAGCGAATC Mutant CTTGCTAGCGAATC The substitution shown seems to have created a stop codon. What further information do you need to be confident that this is so 2. What type of mutation is the following shown as mRNA 3. Can a missense mutation of proline to histidine be made with a G C A T transition-causing mutagen What about a proline-to-serine missense mutation 4. By base-pair substitution, what are all the synonymous changes that...
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Figure 5-9 Visualization of single-stranded DNA transfer in conjugating E. coli cells, using special fluorescent antibodies. Parental Hfr strains A are black with red DNA. The red is from binding of an antibody to a protein normally attached to DNA. The recipient cells B are green due to the presence of the GFP protein and because they are mutant for a certain gene they do not bind the special protein that binds to antibody. When single-stranded DNA enters the recipient, it promotes atypical...
Linkage symbolism and terminology
The work of Morgan showed that linked genes in a dihybrid may be present in one of two basic conformations. In one, the two dominant or wild-type alleles are present on the same homolog as in Figure 4-2 this arrangement is called a cis conformation. In the other, they are on different homologs, in what is called a trans conformation. The two conformations are written as follows Alleles on the same homolog have no punctuation between them. A slash symbolically separates the two homologs. Alleles...
Dna Dva
Figure 8-10a gives a physical picture of elongation. Inside the bubble, the last 10 nucleotides added to the RNA chain form an RNA DNA hybrid by complementary base pairing with the template strand. b Termination intrinsic mechanism b Termination intrinsic mechanism Figure 8-10 Elongation and termination of transcription. The four subunits of RNA polymerase are shown as a single ellipse-like shape surrounding the transcription bubble. a Elongation Synthesis of an RNA strand complementary to the...