Textbook Question
Provide a comprehensive definition of heterochromatin and list as many examples as you can.
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Ch. 11 - Chromosome Structure and DNA Sequence Organization
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 11, Problem 14
Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?
Verified step by step guidance1
Begin by defining SINEs (Short Interspersed Nuclear Elements) and LINEs (Long Interspersed Nuclear Elements) as two types of transposable elements found in the genome, emphasizing their role in genome structure and evolution.
Explain the structural differences: SINEs are short sequences, typically around 100-300 base pairs, and do not encode proteins, whereas LINEs are much longer, often several thousand base pairs, and contain open reading frames that encode proteins necessary for their own mobilization.
Describe how LINEs have the machinery (such as reverse transcriptase and endonuclease) that allows them to copy and insert themselves into new locations in the genome, which is a key feature of retrotransposons.
Clarify that SINEs lack this machinery and rely on the proteins produced by LINEs to transpose, making them non-autonomous elements.
Conclude by explaining that LINEs are called retrotransposons because they transpose through an RNA intermediate that is reverse transcribed back into DNA before insertion, a process similar to retroviral replication.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Structure of SINEs (Short Interspersed Nuclear Elements)
SINEs are short DNA sequences, typically 100-300 base pairs long, that do not encode proteins. They rely on other elements for their mobility and are derived from small RNA genes like tRNA. SINEs are non-autonomous, meaning they cannot transpose by themselves.
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05:30
Human Transposable Elements
Structure of LINEs (Long Interspersed Nuclear Elements)
LINEs are longer DNA sequences, usually 6,000 base pairs, that encode proteins necessary for their own retrotransposition, such as reverse transcriptase. They are autonomous elements capable of copying and inserting themselves into new genomic locations.
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05:30Human Transposable Elements
Retrotransposons and Their Mechanism
Retrotransposons are genetic elements that move within the genome via an RNA intermediate, which is reverse-transcribed back into DNA before insertion. LINEs are called retrotransposons because they encode enzymes enabling this copy-and-paste mechanism, unlike SINEs which depend on LINE machinery.
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03:14Eukaryotic Transposable Elements
Related Practice
Textbook Question
Contrast the various categories of repetitive DNA.
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Textbook Question
Define satellite DNA. Describe where it is found in the genome of eukaryotes and its role as part of chromosomes.
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Textbook Question
Mammals contain a diploid genome consisting of at least 10⁹ bp. If this amount of DNA is present as chromatin fibers, where each group of 200 bp of DNA is combined with 9 histones into a nucleosome and each group of 6 nucleosomes is combined into a solenoid, achieving a final packing ratio of 50, determine:
(a) the total number of nucleosomes in all fibers,
(b) the total number of histone molecules combined with DNA in the diploid genome, and
(c) the combined length of all fibers.
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Textbook Question
Assume that a viral DNA molecule is a 50-µm-long circular strand with a uniform 20-Å diameter. If this molecule is contained in a viral head that is a 0.08-µm-diameter sphere, will the DNA molecule fit into the viral head, assuming complete flexibility of the molecule? Justify your answer mathematically.
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Textbook Question
How many base pairs are in a molecule of phage T2 DNA 52-µm long?
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