Concept explainers
Roberts syndrome is a rare inherited disorder characterized by facial defects as well as severe limb shortening, extra digits, and deformities of the knees and ankles. A cytogenetic analysis of patients with Roberts syndrome, using Giemsa staining or C-banding, reveals that there is premature separation of centromeres and other heterochromatic regions during mitotic metaphase instead of anaphase. A couple with an affected infant is contacted by a local organization dedicated to promoting research on rare genetic diseases, asking if they can photograph the infant as part of a campaign to obtain funding for these conditions. The couple learned that the privacy of such medical images is not well protected, and they often are subsequently displayed on public websites. The couple was torn between helping to raise awareness and promoting research on this condition and sheltering their child from having his images used inappropriately. Several interesting questions are raised.
In Roberts syndrome, how could premature separation of centromeres during mitosis cause the wide range of
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Concepts of Genetics (12th Edition)
- a. Manually, using a pencil, draw a cell in anaphase II from an organism in which 2n = 2 and each chromosome is metacentric. b. Given that each G1 nucleus from this organism contains 16 picograms of DNA, how many picograms of chromosomal DNA would you expect in the cell shown here?arrow_forwardIn the following schematic drawing of a Holliday junction,one chromatid is shown in red, and the homologous chromatidis shown in blue. The red chromatid carries a dominant allelelabeled A and a recessive allele labeled b, whereas the blue chromatidcarries a recessive allele labeled a and a dominant allelelabeled B. Where would the DNA strands have to be cut to produce recombinantchromosomes? Would they be cut at sites 1 and 3, or at sites2 and 4? What would be the genotypes of the two recombinantchromosomes?arrow_forwardHumans and many other complex organisms are diploid, possessing two sets of genes, one inherited from the mother and one from the father. However, a number of eukaryotic organisms spend most of their life cycles in a haploid state. Many of these eukaryotes, such as Neurospora and yeast, still undergo meiosis and sexual reproduction, but most of the cells that make up the organism are haploid. Considering that haploid organisms are fully capable of sexual reproduction and generating genetic variation, why are most complex eukaryotes diploid? In other words, what might be the evolutionary advantage of existing in a diploid state instead of a haploid state? And why might a few organisms, such as Neurospora and yeast, exist as haploids?arrow_forward
- A somatic cell has the genotype DdEe. All chromosomes in this organism are metacentric. Show metaphase and the results of mitosis if the D and E locus are linked on the same chromosome in trans configuration. A sexually reproducing organism has the following phenotype DdEeAaTt: The D and E loci are on the same arm of a metacentric chromosome in cis configuration. The A locus is on the long arm of an acrocentric chromosome and the T locus is on a telocentric chromosome. 2.1. What is the haploid number of this organism? 2.2. Using diagrams show a ceii at metaphase of mitosis and show the results of mitosis.arrow_forwardFor below problem, consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text. Question: Assume that each gamete resulting from Problem 29 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?arrow_forwardconsider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap, etc.). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a large cut-up paper bag and work with another student as you deal with these problems. Such cooperative learning may be a useful approach as you solve problems throughout the text. Draw all possible combinations of chromatids during anaphase II in meiosis.arrow_forward
- A cytogeneticist is studying the cells from an abnormal female monkey. In some cells, she finds that both X-chromosomes are active (i.e. not packaged into a Barr body), although one of the X-chromosomes appears shorter. She also finds that one of the autosomes are packaged as a Barr body, and she suspects that a translocation event might have been involved. By referring to the mechanism of X-chromosome inactivation, explain the observations made by the scientistarrow_forwardAssume that the diploid number of a certain species is four chromosomes, two large and two small (2n=4). a) Of the following figures, which represents a 3n (triploid) cell in mitotic metaphase? b) For each of the wrong answers from part (a) above, explain briefly why it cannot represent a triploid cell in mitotic metaphase.arrow_forwardColchicine is a chemical mutagen that inhibits the spindle formation and prevents anaphase, which retains the cell’s single restitution nucleus (doubled chromosome number). Suppose that an onion (2n=16) is subjected to three consecutive rounds of colchicine treatment, what will be the resulting chromosome number of the treated onion?arrow_forward
- Variations in Chromosome NumberAneuploidy Describe the process of nondisjunction and explain when it takes place during cell division.arrow_forwardDuring a practical, a group of biology students are tasked to study the cell cycle of an insect. This insect has the karyotype 2n=6, with genotype Aa Bb Ee HH. The students must draw a G2 cell about to enter meiosis, using red lines for maternal chromosomes, blue lines for paternal chromosomes and black dots to represent centromeres. The drawing provided by the students is shown below. a) Identify three mistakes the students made when producing this diagram. In your answer only refer to elements already present in the figure. (3) b) This fly is used in a testcross. What is the probability of producing a fly with genotype Aa bb ee Hh?arrow_forwardA diploid species has 3 pairs of chromosomes in its somatic cells. In males, the first pair is large submetacentric[1]; the second is medium acrocentric[2], and the third is small telocentric[3]. In females, the first two pairs are like those of the males while the third is large metacentric[4][5], with satellite4 Illustrate the karyograms (drawing/picture of the chromosome) of the following: A triploid cell in females tetrasomic cell in males tetraploid cell in females [1] submetacentric --centrosome is just above the middle of the chromosome [2] acrocentric --centrosome is much higher location than submetacentric so that the “p” arm of the chromosome is much shorter than the q arm [3] telocentric --the centromere is at the end of the chromosome [4] metacentric --centrosome is in the middle of the chromosome; thus the “p-arm” and the “q-arm” or both arms of the chromosome are equal in length [5] satellite-a constriction in an arm of a chromosome, aside…arrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning