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Questions and Answers
What is the function of telomeres in chromosomes?
What is the function of telomeres in chromosomes?
Which process describes the separation of double-stranded DNA when heated?
Which process describes the separation of double-stranded DNA when heated?
What characterizes highly repetitive DNA in eukaryotic genomes?
What characterizes highly repetitive DNA in eukaryotic genomes?
What experiment shows that regions of genomic DNA have different hybridisation rates?
What experiment shows that regions of genomic DNA have different hybridisation rates?
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What is indicated by the presence of multiple hybridisation rates within DNA?
What is indicated by the presence of multiple hybridisation rates within DNA?
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What defines eukaryotic chromosomes as homologous?
What defines eukaryotic chromosomes as homologous?
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What is included in the description of a karyotype?
What is included in the description of a karyotype?
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How are cells commonly arrested during cell division for karyotyping?
How are cells commonly arrested during cell division for karyotyping?
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Which region of DNA is specifically stained by Giemsa dye in karyotyping?
Which region of DNA is specifically stained by Giemsa dye in karyotyping?
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What does a chromatid consist of following DNA replication?
What does a chromatid consist of following DNA replication?
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What role does the centromere play during cell division?
What role does the centromere play during cell division?
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Which chromosomes are referred to as sex chromosomes in humans?
Which chromosomes are referred to as sex chromosomes in humans?
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What characteristic do autosomal chromosomes exhibit in humans?
What characteristic do autosomal chromosomes exhibit in humans?
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Which statement correctly describes prokaryotic chromosomes?
Which statement correctly describes prokaryotic chromosomes?
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What is the definition of 'nucleoid' in prokaryotic cells?
What is the definition of 'nucleoid' in prokaryotic cells?
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Which of the following statements is true regarding eukaryotic chromosomes?
Which of the following statements is true regarding eukaryotic chromosomes?
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How are genomes defined in relation to chromosome numbers?
How are genomes defined in relation to chromosome numbers?
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What distinguishes viral genomes from bacterial and eukaryotic genomes?
What distinguishes viral genomes from bacterial and eukaryotic genomes?
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What is the term for organisms that have two sets of chromosomes?
What is the term for organisms that have two sets of chromosomes?
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What key difference exists in the origins of replication between eukaryotic and prokaryotic chromosomes?
What key difference exists in the origins of replication between eukaryotic and prokaryotic chromosomes?
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How do the structural forms of bacterial DNA differ from eukaryotic DNA?
How do the structural forms of bacterial DNA differ from eukaryotic DNA?
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Study Notes
Chromosome Structure
- Chromosomes are thread-like structures made of DNA and protein
- All living organisms have chromosomes
- They are the vehicle of heredity
Prokaryotic vs. Eukaryotic DNA
- Prokaryotic DNA is typically a single, circular chromosome located in the cytoplasm
- Eukaryotic DNA is multiple, linear chromosomes located in the nucleus
- Prokaryotic DNA is not usually wrapped around histones, while Eukaryotic DNA is
Bacterial Chromosomes
- Bacterial chromosomes are typically circular and supercoiled
- They are folded into twisted loops, which are clumped together in the nucleoid region
- Bacterial chromosomes are typically attached to proteins
Prokaryotic DNA
- Prokaryotic DNA usually contains a single origin of replication
- This origin is where DNA replication begins
Viral Chromosomes
- Viral chromosomes can be either DNA or RNA
- Viral DNA is packaged within a protein coat called a capsid
Eukaryotic Chromosomes
- Eukaryotic chromosomes are usually linear and tightly packaged with histone proteins to create chromatin
- Unlike prokaryotic cells, eukaryotic cells have a nucleus where the chromosomes are located
- Eukaryotic chromosomes contain many origins of replication per chromosome
- Each species has its own distinct chromosome number
- Eukaryotic chromosomes exist in pairs, this is called diploid
Genome
- The entire genetic material of an organism
- In humans, the genome is made up of 23 pairs of chromosomes for a total of 46 chromosomes
- The genome size can be extremely different between species
Eukaryotic Chromosomes
- Autosomal chromosomes are the non-sex chromosomes (e.g. human chromosomes 1 to 22)
- Sex chromosomes (e.g. human X and Y chromosomes) determine an individual's sex (XX = female, XY = male)
Homologous Chromosomes
- Homologous chromosomes are pairs of chromosomes that contain the same genes, but may have different versions (alleles)
Karyotype
- A karyotype is a physical description of the chromosomes within a cell, including information about their number, type, shape, banding patterns, and other cytogenetic features
- Karyotyping can be used to identify chromosomal abnormalities
Karyotyping
- To perform karyotyping, cells are often arrested during cell division using colchicine, a tubulin inhibitor
- Chromosomes are often stained with Giemsa, which binds to phosphate groups in DNA and creates a banding pattern
Karyotype - G-banding
- Giemsa staining allows for the identification of distinct banding patterns on each chromosome
- These patterns help to distinguish the different chromosomes in a karyotype
Chromatid
- Each chromosome is made up of two identical structures called chromatids
- These chromatids are attached together at the centromere
Basic Structure of a Eukaryotic Chromosome
- Eukaryotic chromosomes are made up of a centromere, telomeres, and the arms of the chromosome
Centromere
- The centromere is a specialized region of heterochromatin where the two chromatids are joined
- The centromere plays a crucial role in the proper segregation of chromosomes during cell division
- Chromosomes can be classified based on the location of the centromere
- A metacentric chromosome has a centromere in the middle of the chromosome.
- A submetacentric chromosome has a centromere closer to one end than to the other.
- An acrocentric chromosome has a centromere very close to one end, with the result that one arm is extremely short relative to the other arm.
- A telocentric chromosome has a centromere at the end of the chromosome, only possessing one arm.
Telomeres
- Telomeres are repetitive sequences found at the ends of chromosomes
- Help to protect the ends of chromosomes from degradation and fusion
Complexity of Eukaryotic Chromosomes & Genomes
- Eukaryotic genomes are much more complex than prokaryotic genomes
Complexity in Eukaryotic Genomes
- If double-stranded DNA is denatured by heating, it separates into two single strands
- The temperature at which this happens is called the melting temperature
- Reannealing complementary strands of genomic DNA from eukaryotes shows regions with very different hybridization (reannealing) rates
- These differences in hybridization rates suggest that there are at least three types of DNA regions within the eukarytic genome:
- Highly repetitive DNA
- Moderately repetitive DNA
- Unique DNA
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Description
Explore the fascinating world of chromosome structures in both prokaryotic and eukaryotic cells. This quiz covers the differences in DNA organization, the nature of bacterial and viral chromosomes, and the implications for heredity. Test your understanding of these fundamental biological concepts!
