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Questions and Answers of Biology

Aneuploidy is typically detrimental, whereas polyploidy is sometimes beneficial, particularly in plants. Discuss why you think this is the case.
Explain how aneuploidy, deletions, and duplications cause genetic imbalances. Why do you think that deletions and monosomies are more detrimental than duplications and trisomies?
Female fruit flies homozygous for the X-linked white-eye allele are crossed to males with red eyes. On very rare occasions, an offspring is a male with red eyes. Assuming these rare offspring are not
A cytogeneticist has collected tissue samples from members of the same butterfly species. Some of the butterflies were located in Canada, and others were found in Mexico. Upon karyotyping, the
Why do you think that human trisomies 13, 18, and 21 can survive but the other trisomies are lethal? Even though X chromosomes are large, aneuploidies of this chromosome are also tolerated. Explain
A zookeeper has collected a male and a female lizard that look like they belong to the same species. They mate with each other and produce phenotypically normal offspring. However, the offspring are
What is endopolyploidy? What is its biological significance?
What is mosaicism? How is it produced?
Explain how polytene chromosomes of Drosophila melanogaster are produced and how they form a six-armed structure.
Describe some of the advantages of polyploid plants. What are the consequences of having an odd number of chromosome sets?
How does a chromosomal duplication occur?
While conducting field studies on a chain of islands, you decide to karyotype two phenotypically identical groups of turtles, which are found on different islands. The turtles on one island have 24
The kidney bean, Phaseolus vulgaris, is a diploid species containing a total of 22 chromosomes in somatic cells. How many possible types of trisomic individuals could be produced in this species?
The karyotype of a young girl who is affected with familial Down syndrome revealed a total of 46 chromosomes. Her older brother, however, who is phenotypically unaffected, actually had 45
A triploid plant has 18 chromosomes (i.e., 6 chromosomes per set). If we assume a gamete has an equal probability of receiving one or two copies of each of the six types of chromosome, what are the
Describe three naturally occurring ways that chromosome number can change.
Meiotic nondisjunction is much more likely than mitotic non-disjunction. Based on this observation, would you conclude that meiotic nondisjunction is usually due to nondisjunction during meiosis I or
A woman who is heterozygous, Bb, has brown eyes. B (brown) is a dominant allele, and b (blue) is recessive. In one of her eyes, however, there is a patch of blue color. Give three different
What is an allodiploid? What factor determines the fertility of an allodiploid? Why are allotetraploids more likely to be fertile?
What is a gene family? How are gene families produced over time? With regard to gene function, what is the biological significance of a gene family?
What are homeologous chromosomes?
Table 8.1 shows that Turner syndrome occurs when an individual inherits one X chromosome but lacks a second sex chromosome. Can Turner syndrome be due to nondisjunction during oogenesis,
Male honeybees, which are monoploid, produce sperm by meiosis. Explain what unusual event (compared with other animals) must occur during spermatogenesis in honeybees to produce sperm. Does this
Following a gene duplication, two genes will accumulate different mutations, causing them to have slightly different sequences. In Figure 8.7, which pair of genes would you expect to have more
Two chromosomes have the following order of genes: Normal: ABC centromere D E F G H I Abnormal: A B G F E D centromere CHI Does the abnormal chromosome have a pericentric or paracentric inversion?
An inversion heterozygote has the following inverted chromosome:What would be the products if a crossover occurred between genes H and / on one inverted and one normal chromosome?
An inversion heterozygote has the following inverted chromosome:What would be the products if a crossover occurred between genes H and / on one inverted and one normal chromosome?
Explain why inversions and reciprocal translocations do not usually cause a phenotypic effect. In a few cases, however, they do. Explain how.
What is the main goal of comparative genome hybridization? Explain how the ratio of green to red fluorescence provides information about chromosome structure.
Let's suppose a researcher conducted comparative genomic hybridization (see Figure 8.9) and accidentally added twice as much (red) DNA from normal cells. What green-to-red ratio would you expect in a
With regard to the analysis of chromosome structure, explain the experimental advantage that polytene chromosomes offer. Discuss why changes in chromosome structure are more easily detected in
Describe the steps you would take to produce a tetraploid plant from a diploid plant.
It is an exciting time to be a plant breeder because so many options are available for the development of new types of agriculturally useful plants. Let's suppose you wish to develop a seedless
What is a G band? Discuss how G bands are useful in the analysis of chromosome structure.
A female fruit fly has one normal X chromosome and one X chromosome with a deletion. The deletion is in the middle of the X chromosome and is about 10% of the entire length of the X chromosome. If
A chromosome involved in a reciprocal translocation also has an inversion. In addition, the cell contains two normal chromosomes.Make a drawing that shows how these chromosomes will pair during
Besides the ones mentioned in this textbook, look for other examples of variations in euploidy. Perhaps you might look in more advanced textbooks concerning population genetics, ecology, or the like.
Cell biology textbooks often discuss cellular proteins encoded by genes that are members of a gene family. Examples of such proteins include myosins and glucose transporters. Look through a cell
Discuss how variation in chromosome number has been useful in agriculture.
Make a side-by-side drawing of two DNA helices: one with 10 bp per 360° turn and the other with 15 bp per 360° turn.
Discuss the differences in the structural features of B DNA and Z DNA.
What parts of a nucleotide (namely, phosphate, sugar, and/or bases) occupy the major and minor grooves of double-stranded DNA, and what parts are found in the DNA backbone? If a DNA-binding protein
List the structural differences between DNA and RNA.
Draw the structure of deoxyribose and number the carbon atoms. Describe the numbering of the carbon atoms in deoxyribose with regard to the directionality of a DNA strand. In a DNA double helix, what
Write out a sequence of an RNA molecule that could form a stem-loop with 24 nucleotides in the stem and 16 nucleotides in the loop.
Compare the structural features of a double-stranded RNA structure with those of a DNA double helix.
Which of the following DNA double helices would be more difficult to separate into single-stranded molecules by treatment with heat, which breaks hydrogen bonds? A. GGCGTACCAGCGCAT CCGCATGGTCGCGTA B.
Discuss the structural significance of complementary in DNA and in RNA.
After the DNA from type S bacteria is exposed to type R bacteria, list all of the steps that you think must occur for the bacteria to start making a capsule.
Let's suppose you have recently identified an organism that was scraped from an asteroid that hit the earth. (Fortunately, no one was injured.) When you analyze this organism, you discover that its
On further analysis of the DNA described in conceptual question C21, you discover that the triplex DNA in this alien organism is composed of a double helix, with the third helix wound within the
A DNA-binding protein recognizes the following double-stranded sequence: 5'-GCCCGGGC-3' 3'-CGGGCCCG-5' This type of double-stranded structure could also occur within the stem region of an RNA
In what ways are the structures of an a helix in proteins and the DNA double helix similar, and in what ways are they different?
The base composition of an RNA virus was analyzed and found to be 14.1% A, 14.0% U, 36.2% G, and 35.7% C. Would you conclude that the viral genetic material is single-stranded RNA or double-stranded
Look up the meaning of the word transformation in a dictionary and explain whether it is an appropriate word to describe the transfer of genetic material from one organism to another.
A medium-sized human chromosome contains about 100 million bp. If the DNA were stretched out in a linear manner, how long would it be?
A double-stranded DNA molecule is 1 cm long, and the percentage of adenine is 15%. How many cytosines would be found in this DNA molecule?
Could single-stranded DNA form a stem-loop structure? Why or why not?
As described in Chapter 15, the methylation of cytosine bases can have an important effect on gene expression. For example, the methylation of cytosines may inhibit the transcription of genes. A
An RNA molecule has the following sequence: Region 1 Region 2 Region 3 5'-CAUCCAUCCAUUCCCCAUCCGAUAAGGGGAAUGGAUCCGAAUGGAUAAC-3' Parts of region 1 can form a stem-loop with region 2 and with region 3.
What are the building blocks of a nucleotide? With regard to the 5' and 3' positions on a sugar molecule, how are nucleotides linked together to form a strand of DNA?
Draw the structure of guanine, guanosine, and deoxyguanosine triphosphate.
Describe how bases interact with each other in the double helix. This discussion should address the issues of complementary, hydrogen bonding, and base stacking.
Genetic material acts as a blueprint for an organism's traits. Explain how Griffith's experiments indicated that genetic material was being transferred to the type R bacteria.
With regard to the experiment described in Figure 9.2, answer the following: A. List several possible reasons why only a small percentage of the type R bacteria was converted to type S. B. Explain
An interesting trait that some bacteria exhibit is resistance to killing by antibiotics. For example, certain strains of bacteria are resistant to tetracycline, whereas other strains are sensitive to
With regard to the experiment of Figure 9.5, answer the following: A. Provide possible explanations why some of the DNA is in the supernatant. B. Plot the results if the radioactivity in the pellet,
Does the experiment of Figure 9.5 rule out the possibility that RNA is the genetic material of T2 phage? Explain your answer. If it does not, could you modify Hershey and Chases approach to show that
In this chapter, we considered two experiments-one by Avery, MacLeod, and McCarty and the second by Hershey and Chase-that indicated DNA is the genetic material. Evaluate the strengths and weaknesses
The type of model building used by Pauling and Watson and Crick involved the use of ball-and-stick units. Now we can do model building on a computer screen. Even though you may not be familiar with
With regard to Chargaff s experiment described in Figure 9.13, answer the following: A. What is the purpose of paper chromatography? B. Explain why it is necessary to remove the bases in order to
Gierer and Schramm exposed plant tissue to purified RNA from tobacco mosaic virus, and the plants developed the same types of lesions as if they had been exposed to the virus itself. What would be
Try to propose structures for a genetic material that are substantially different from the double helix. Remember that the genetic material must have a way to store information and a way to be
How might you provide evidence that DNA is the genetic material in mice?
On rare occasions, a chromosome can suffer a small deletion that removes the centromere. When this occurs, the chromosome usually is not found within subsequent daughter cells. Explain why a
What is the function of a centromere? At what stage of the cell cycle would you expect the centromere to be the most important?
Describe the characteristics of highly repetitive DNA.
Describe the structures of a nucleosome and a 30-nm fiber.
Beginning with the G, phase of the cell cycle, describe the level of compaction of the eukaryotic chromosome. How does the level of compaction change as the cell progresses through the cell cycle?
If you assume the average length of linker DNA is 50 bp, approximately how many nucleosomes are found in the haploid human genome, which contains 3 billion bp?
Draw a picture depicting the binding between the nuclear matrix and MARs.
Compare heterochromatin and euchromatin. What are the differences between them?
Compare the structure and cell localization of chromosomes during interphase and M phase.
What types of genetic activities occur during interphase? Explain why these activities cannot occur during M phase.
In Part II of this textbook, we considered inheritance patterns for diploid eukaryotic species. Bacteria frequently contain two or more nucleoids. With regard to genes and alleles, how is a bacterium
Lets assume the linker DNA averages 54 bp in length. How many molecules of H2A would you expect to find in a DNA sample that is 46,000 bp in length?
What are the roles of the core histone proteins compared with the role of histone HI in the compaction of eukaryotic DNA?
A typical eukaryotic chromosome found in humans contains about 100 million bp of DNA. As described in Chapter 9, one bp of DNA has a linear length of 0.34 nm. A. What is the linear length of the DNA
Which of the following terms should not be used to describe a Barr body? A. Chromatin B. Euchromatin C. Heterochromatin D. Chromosome E. Genome
Discuss the differences in the compaction levels of metaphase chromosomes compared with interphase chromosomes. When would you expect gene transcription and DNA replication to take place, during M
What is an SMC protein? Describe two examples.
Describe the two main mechanisms by which the bacterial DNA becomes compacted.
As described in Chapter 9, one bp of DNA is approximately 0.34 nm in length. A bacterial chromosome is about 4 million bp in length and is organized into about 100 loops that are about 40,000 bp in
Why is DNA supercoiling called supercoiling rather than just coiling? Why is positive supercoiling called overwinding and negative supercoiling called underwinding? How would you define the terms
Coumarins and quinolones are two classes of drugs that inhibit bacterial growth by directly inhibiting DNA gyrase. Discuss two reasons why inhibiting DNA gyrase also inhibits bacterial growth.
Take two pieces of string that are approximately 10 inches each, and create a double helix by wrapping them around each other to make 10 complete turns. Tape one end of the strings to a table, and
Try to explain the function of DNA gyrase with a drawing.
Two circular DNA molecules, which we will call molecule A and molecule B, are topoisomers of each other. When viewed under the electron microscope, molecule A appears more compact than molecule B.
Let's suppose you have isolated DNA from a cell and viewed it under a microscope. It looks supercoiled. What experiment would you perform to determine if it is positively or negatively super-coiled?
We seem to know more about the structure of eukaryotic chromosomal DNA than bacterial DNA. Discuss why you think this is so, and list several experimental procedures that have yielded important

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