The accompanying chromosome diagram represents a eukaryotic chromosome prepared with Giemsa stain. Indicate the heterochromatic and euchromatic regions of the chromosome, and label the chromosome's centromeric and telomeric regions.

Do you expect the centromeric region to contain heterochromatin? Why or why not?

The accompanying chromosome diagram represents a eukaryotic chromosome prepared with Giemsa stain. Indicate the heterochromatic and euchromatic regions of the chromosome, and label the chromosome's centromeric and telomeric regions.

Why are expressed genes not found in the telomeric region of chromosomes?

The accompanying chromosome diagram represents a eukaryotic chromosome prepared with Giemsa stain. Indicate the heterochromatic and euchromatic regions of the chromosome, and label the chromosome's centromeric and telomeric regions.

Are you more likely to find the DNA sequence encoding the digestive enzyme amylase in a heterochromatic, euchromatic, centromeric, or telomeric region? Explain your reasoning.

Histone protein H4 isolated from pea plants and cow thymus glands contains 102 amino acids in both cases. A total of 100 of the amino acids are identical between the two species. Give an evolutionary explanation for this strong amino acid sequence identity based on what you know about the functions of histones and nucleosomes.

A survey of organisms living deep in the ocean reveals two new species whose DNA is isolated for analysis. DNA samples from both species are treated to remove nonhistone proteins. Each DNA sample is then treated with DNase I that cuts DNA not protected by histone proteins but is unable to cut DNA bound by histone proteins. Following DNase I treatment, DNA samples are subjected to gel electrophoresis, and the gels are stained to visualize all DNA bands in the gel. The staining patterns of DNA bands from each species are shown in the figure. The number of base pairs in small DNA fragments is shown at the left of the gel. Interpret the gel results in terms of chromatin organization and the spacing of nucleosomes in the chromatin of each species.

In humans that are XX/XO mosaics, the phenotype is highly variable, ranging from females who have classic Turner syndrome symptoms to females who are essentially normal. Likewise, XY/XO mosaics have phenotypes that range from Turner syndrome females to essentially normal males. How can the wide range of phenotypes be explained for these sex-chromosome mosaics?

A plant breeder would like to develop a seedless variety of cucumber from two existing lines. Line A is a tetraploid line, and line B is a diploid line. Describe the breeding strategy that will produce a seedless line, and support your strategy by describing the results of crosses.

In Drosophila, seven partial deletions (1 to 7) shown as gaps in the following diagram have been mapped on a chromosome. This region of the chromosome contains genes that express seven recessive mutant phenotypes, identified in the following table as a through g. A researcher wants to determine the location and order of genes on the chromosome, so he sets up a series of crosses in which flies homozygous for a mutant allele are crossed with flies homozygous for a partial deletion. The progeny are scored to determine whether they have the mutant phenotype ('m' in the table) or the wild-type phenotype ('+' in the table). Use the partial deletion map and the table of progeny phenotypes to determine the order of genes on the chromosome.

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

Do you expect both experimental lines to be fertile? Why or why not?

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

How many chromosomes from the hexaploid line are contributed to experimental variety 1? To experimental variety 2?

Two experimental varieties of strawberry are produced by crossing a hexaploid line that contains 48 chromosomes and a tetraploid line that contains 32 chromosomes. Experimental variety 1 contains 40 chromosomes, and experimental variety 2 contains 56 chromosomes.

How many chromosomes from the tetraploid lines are contributed to experimental variety 1? To experimental variety 2?

In the tomato, Solanum esculentum, tall (D−)(D−) is dominant to dwarf (dd) plant height, smooth fruit (P−) is dominant to peach fruit (pp), and round fruit shape (O−) is dominant to oblate fruit shape (oo). These three genes are linked on chromosome 1 of tomato in the order dwarf–peach–oblate. There are 12 map units between dwarf and peach and 17 map units between peach and oblate. A trihybrid plant (DPO/dpo) is test-crossed to a plant that is homozygous recessive at the three loci (dpo/dpo). The accompanying table shows the progeny plants. Identify the mechanism responsible for the resulting data that do not agree with the established genetic map.

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

Explain how this is possible.

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

How many chromosomes do you expect to see in karyotypes of the parents?

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

What term best describes this kind of chromosome abnormality?

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes? Explain your answer.

Experimental evidence demonstrates that the nucleosomes present in a cell after the completion of S phase are composed of some 'old' histone dimers and some newly synthesized histone dimers. Describe the general design for an experiment that uses a protein label such as ³⁵S to show that nucleosomes are often a mixture of old and new histone dimers following DNA replication.

DNase I cuts DNA that is not protected by bound proteins but is unable to cut DNA that is complexed with proteins. Human DNA is isolated, stripped of its nonhistone proteins, and mixed with DNase I. Samples are removed after 30 minutes, 1 hour, and 4 hours and run separately in gel electrophoresis. The resulting gel is stained to make all DNA fragments in it visible, and the results are shown in the figure. DNA fragment sizes in base pairs (bp) are estimated by the scale to the left of the gel. Examine the gel results and speculate why longer DNase I treatment produces different results.

DNase I cuts DNA that is not protected by bound proteins but is unable to cut DNA that is complexed with proteins. Human DNA is isolated, stripped of its nonhistone proteins, and mixed with DNase I. Samples are removed after 30 minutes, 1 hour, and 4 hours and run separately in gel electrophoresis. The resulting gel is stained to make all DNA fragments in it visible, and the results are shown in the figure. DNA fragment sizes in base pairs (bp) are estimated by the scale to the left of the gel. Draw a conclusion about the organization of chromatin in the human genome from this gel.

Genomic DNA from the nematode worm Caenorhabditis elegans is organized by nucleosomes in the manner typical of eukaryotic genomes, with 145 bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the 10-nm fiber structure. Suppose researchers mix a sample of 10-nm–fiber chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain all the DNA fragments in the gel.

Approximately what range of DNA fragment sizes do you expect to see in the stained electrophoresis gel? How many bands will be visible on the gel?

Genomic DNA from the nematode worm Caenorhabditis elegans is organized by nucleosomes in the manner typical of eukaryotic genomes, with 145 bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the 10-nm fiber structure. Suppose researchers mix a sample of 10-nm–fiber chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain all the DNA fragments in the gel.

Explain the origin of DNA fragments seen in the gel.

Genomic DNA from the nematode worm Caenorhabditis elegans is organized by nucleosomes in the manner typical of eukaryotic genomes, with 145 bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the 10-nm fiber structure. Suppose researchers mix a sample of 10-nm–fiber chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain all the DNA fragments in the gel.

How do the expected results support the 10-nm–fiber model of chromatin?

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

Describe how the banding pattern of the island population chromosome most likely evolved from the mainland chromosome. What term or terms describe the difference between these chromosomes?

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

Draw the synapsis of these homologs during prophase I in hybrids produced from the cross of mainland with island deer.

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

In a mainland–island hybrid deer, recombination takes place in band q1 of the homologous chromosomes. Draw the gametes that result from this event.

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population.

Suppose that 40% of all meioses in mainland–island hybrids involve recombination somewhere in the chromosome region between q2.1 and p2. What proportion of the gametes of hybrid deer are viable? What is the cause of the decreased proportion of viable gametes in hybrids relative to the parental populations?

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Carefully examine and redraw these chromosomes in any valid metaphase I alignment. Draw and label the metaphase plate, and label each chromosome with its assigned letter. 

A eukaryote with a diploid number of 2n=6 carries the chromosomes shown below and labeled (a) to (f).

Explain how you determined the correct alignment of homologous chromosomes on opposite sides of the metaphase plate. 

Human chromosome 5 and the corresponding chromosomes from chimpanzee, gorilla, and orangutan are shown here. Describe any structural differences you see in the other primate chromosomes in relation to the human chromosome.

For the following crosses, determine as accurately as possible the genotypes of each parent, the parent in whom nondisjunction occurs, and whether nondisjunction takes place in the first or second meiotic division. Both color blindness and hemophilia, a blood-clotting disorder, are X-linked recessive traits. In each case, assume the parents have normal karyotypes.

A man and a woman who each has the wild-type phenotype have a son with Klinefelter syndrome (XXY) who has hemophilia.