Podcast
Questions and Answers
What is the purpose of the characteristic banding pattern on chromosomes?
Which arm of the chromosome is designated as 'p'?
What technique is used to visualize all pairs of chromosomes in different colors?
What limitation exists with the number of spectrally-distinct fluorophores used in spectral karyotyping?
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How are the stained regions on chromosomes typically organized?
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What is a primary characteristic of prokaryotic chromosomes?
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Which of the following statements accurately describes plasmids?
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What is the function of a telomere in a chromosome?
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What distinguishes the centromere of a chromosome?
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How are prokaryotic chromosomes organized within the cell?
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Which of the following examples displays the characteristic arrangement of circular prokaryotic chromosomes?
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What is a characteristic of chromatid in a chromosome?
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How are chromosomes classified?
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What is the role of fertility (F) factors in plasmids?
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Which type of chromosomal structure has its centromere located at the middle?
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What defines the characteristic banding patterns seen in chromosomes during cytogenetic analysis?
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What is a major function of Bacteriocin Factors?
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Which staining method is commonly used for chromosomal analysis in karyotyping?
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What does digital karyotyping allow scientists to quantify?
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What aspect of chromosomes helps cytogeneticists identify them apart?
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What is NOT a known characteristic of submetacentric chromosomes?
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What is a characteristic of eukaryotic chromosomes compared to prokaryotic chromosomes?
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How many chromosomes do humans have?
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What type of chromatin contains active genes?
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Which of the following statements about eukaryotic chromosomes is true?
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Which of the following best describes heterochromatin?
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What feature differentiates eukaryotic chromosomes from those in prokaryotes?
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Which organism has the highest number of chromosomes based on the examples provided?
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What type of DNA is described as circular and is present in extranuclear locations in eukaryotes?
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Study Notes
Chromosomes
- First observed in 1882 in tumor cells by Walther Fleming
- More easily observed in tumor cells because they are actively replicating.
Eukaryotic Chromosomes
- Multiple linear chromosomes
- Sequestered within a nucleus
- Composed of DNA and proteins (histones)
- Organized into nucleosomes and chromatin
- Active genes make up euchromatin
- Inactive DNA makes up heterochromatin
- Human chromosomes: 46 (22 pairs autosomes + 2 sex chromosomes)
- Example chromosome counts in other eukaryotes:
- Fruit fly: 8
- Kingfisher: 132
- Tobacco: 48
- Adder’s tongue fern: 1260
Extranuclear DNA
- Found in mitochondria and chloroplasts.
- Circular in structure.
- Codes for 5% RNA and polypeptides needed for organelle replication and function.
Plasmids
- Found in Fungi and protozoa.
- Circular molecules of DNA.
- Can be found in multiples (e.g. S. cerevisiae has 70 copies of a plasmid)
Prokaryotic Chromosomes
- Single molecule of DNA in a closed loop.
- Located in the nucleoid.
- Folded into loops of 50,000 - 100,000 bp.
- Examples include:
- Agrobacterium tumefaciens (1 linear, 1 circular)
- Vibrio cholerae (2 circular)
- Bacteria (circular molecule of DNA associated with proteins and RNA)
Parts of a Chromosome
- Telomere: the ends of a chromosome.
- Centromere: primary constriction that divides the chromosome into a short arm (p) and a long arm (q).
- Chromatid: single molecule of DNA
Plasmids
- Small, circular molecules of DNA.
- Few thousand bp to million bp in size.
- Carry information required for replication and cellular traits.
Types of Plasmids
- Fertility (F) factors: facilitate conjugation (transfer of genes).
- Resistance (R) factors: carry genes for resistance to antimicrobial drugs, heavy metals, or toxins.
- Bacteriocin factors: carry genes for proteinaceous toxins (bacteriocin).
- Virulence plasmids: carry genes that contribute to the pathogenicity of bacteria.
Classification of Chromosomes
- Classified by size and position of centromere.
- Metacentric: centromere in the middle of the chromosome.
- Submetacentric: centromere divides the chromosome into 1/3 and 2/3.
- Acrocentric: centromere located near the end of the chromosome.
Cytogenetics
- Cytogeneticists specialize in the study of chromosomes.
- Examine chromosomes under a microscope to identify abnormalities.
- Use three main criteria to distinguish chromosomes.
- Chromosome size
- Position of the centromere
- Characteristic banding patterns: alternating light and dark bands (caused by staining with specific dyes).
Detection of Chromosomal Abnormalities
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Karyotyping:
- Visual analysis of chromosomes in a cell, arranged in pairs based on size and banding patterns.
- "Classic" karyotyping uses Giemsa or Quinacrine staining:
- Giemsa stains phosphate groups.
- Quinacrine binds to adenine-thymine rich regions.
- Chromosomes are arranged with the p arm (short arm) on top and the q arm (long arm) on the bottom.
- Stained regions are numbered from proximal to distal.
-
Spectral Karyotyping:
- Fluorescently labeled probes are used to visualize all chromosomes in different colors.
- A combinatorial labeling technique is used to create many different colors.
- An interferometer is used to capture and analyze the spectral differences.
- Image processing software assigns a pseudo color to each spectrally different chromosome.
-
Digital Karyotyping:
- Quantifies the DNA copy number at specific loci across the entire genome.
- Also known as virtual karyotyping.
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Description
Test your knowledge about chromosomes, including their structures and differences between eukaryotic and prokaryotic cells. Explore the details of extranuclear DNA, plasmids, and chromosome counts in various organisms in this informative quiz.
