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Questions and Answers
What is a key characteristic of the human genome compared to other species?
What is a key characteristic of the human genome compared to other species?
What percentage of human DNA encodes for proteins?
What percentage of human DNA encodes for proteins?
How many genes does the human genome contain?
How many genes does the human genome contain?
What are gene families primarily composed of?
What are gene families primarily composed of?
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Which of the following species is noted for having the highest number of genes?
Which of the following species is noted for having the highest number of genes?
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Which of the following is NOT a mechanism of gene duplication?
Which of the following is NOT a mechanism of gene duplication?
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What contributes to the greater diversity of the human proteome?
What contributes to the greater diversity of the human proteome?
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What is a characteristic feature of the transcriptional complexity in the human genome?
What is a characteristic feature of the transcriptional complexity in the human genome?
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What is the outcome of tandem duplication?
What is the outcome of tandem duplication?
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Which mechanism leads to the presence of extra copies of chromosomes in polyploidy?
Which mechanism leads to the presence of extra copies of chromosomes in polyploidy?
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What is the result of chromosomal translocations?
What is the result of chromosomal translocations?
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Why does one gene in the human genome produce multiple proteins?
Why does one gene in the human genome produce multiple proteins?
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What is the approximate size of the human genome in megabases (Mb)?
What is the approximate size of the human genome in megabases (Mb)?
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DNA polymerase slippage primarily causes which type of genetic variations?
DNA polymerase slippage primarily causes which type of genetic variations?
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What is a characteristic of Class 1 Retrotransposons?
What is a characteristic of Class 1 Retrotransposons?
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What role do repetitive DNA sequences play in tandem duplication?
What role do repetitive DNA sequences play in tandem duplication?
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What can result from the degradation of one gene copy in a duplication scenario?
What can result from the degradation of one gene copy in a duplication scenario?
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Which of the following statements best describes the relationship between the number of genes and the number of proteins in humans?
Which of the following statements best describes the relationship between the number of genes and the number of proteins in humans?
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Which type of transposon utilizes the 'cut and paste' method?
Which type of transposon utilizes the 'cut and paste' method?
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What portion of human DNA is described as being primarily transposable elements or 'other' sequences?
What portion of human DNA is described as being primarily transposable elements or 'other' sequences?
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How can whole genome duplication affect gene functionality?
How can whole genome duplication affect gene functionality?
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What percent of the human genome is made up of mobile DNA elements from Class 2 transposons?
What percent of the human genome is made up of mobile DNA elements from Class 2 transposons?
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What effect can gene duplication have on gene expression?
What effect can gene duplication have on gene expression?
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What are Long Terminal Repeats (LTRs) associated with?
What are Long Terminal Repeats (LTRs) associated with?
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What is one consequence of mutations in duplicated genes?
What is one consequence of mutations in duplicated genes?
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How many Hox clusters do humans possess?
How many Hox clusters do humans possess?
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What is a characteristic of hyaluronidases in humans compared to nematodes?
What is a characteristic of hyaluronidases in humans compared to nematodes?
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What happens to Hox genes with loss-of-function mutations in Drosophila?
What happens to Hox genes with loss-of-function mutations in Drosophila?
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What is an example of a mutation effect in humans related to Hox genes?
What is an example of a mutation effect in humans related to Hox genes?
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How is Hox gene redundancy advantageous to species like fish?
How is Hox gene redundancy advantageous to species like fish?
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What can be a result of loss of a HYAL gene in humans?
What can be a result of loss of a HYAL gene in humans?
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What process can lead to further duplications within Hox gene clusters?
What process can lead to further duplications within Hox gene clusters?
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What is the primary function of microRNAs (miRNAs) in gene regulation?
What is the primary function of microRNAs (miRNAs) in gene regulation?
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Which statement about the human genome's genetic diversity is accurate?
Which statement about the human genome's genetic diversity is accurate?
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Which of the following accurately describes a gene according to the content?
Which of the following accurately describes a gene according to the content?
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What element of gene families arises from duplication events?
What element of gene families arises from duplication events?
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What does the central dogma of molecular biology state?
What does the central dogma of molecular biology state?
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What is a common misconception about the composition of the human genome?
What is a common misconception about the composition of the human genome?
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How can genes be co-transcribed according to the content provided?
How can genes be co-transcribed according to the content provided?
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What aspect of gene inactivation is crucial for the inactive X chromosome?
What aspect of gene inactivation is crucial for the inactive X chromosome?
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Study Notes
Genome Comparisons
- The human genome has a greater information content than other species with around 25,000 protein-encoding genes.
- Despite having similar numbers of genes, C.elegans and Arabidopsis have significantly smaller genomes, and Wheat has a significantly larger genome due to polyploidy.
Human Genome
- The human genome contains more information than just the 25,000 genes, thanks to transcriptional and translational complexity.
- The human proteome contains over 100,000 proteins due to alternative splicing, post-translational modifications, and multiple proteins made from one gene.
Human Genome Complexity
- Human genome complexity stems from multiple transcriptional start sites per gene, alternative splicing, complex non-coding regulatory regions, and extensive post-translational modifications, including glycosylation.
Take Home Message
- A single gene can encode multiple proteins, meaning the 25,000 genes in the human genome can produce over 100,000 proteins.
Human Genome Content
- 1% of human DNA encodes proteins.
- 4% of DNA encodes non-coding RNAs.
- 95% of DNA is made up of transposable elements, repeats, heterochromatin, and other sequences.
Gene Families
- Gene families are groups of closely related genes arising from a single ancestral gene.
- These genes are called paralogues and often cluster together on chromosomes.
- Gene families originate from duplication events.
Mechanisms of Gene Duplication
- Tandem Duplication: Unequal recombination during crossing-over, leading to duplication and deletion events.
- Translocations: Exchange of DNA between chromosomes, resulting in duplications in new chromosomal locations.
- DNA Polymerase Slippage: Small duplications and deletions during DNA replication.
- Transposable Elements: Mobile DNA elements, categorized as retrotransposons (copy and paste) or DNA transposons (cut and paste).
- Whole Genome Duplication: Polyploidy, extra copies of chromosomes.
Gene Duplication Effects
- Redundancy: Genes with the same function, loss of one has minimal effect, loss of both has significant effect.
- Specialization: Duplicated genes acquire novel or specialized functions.
- Degradation: One copy may degrade due to mutation, resulting in a pseudogene.
Duplication and Redundancy
- The loss of one duplicated gene may have little or no effect, as the other performs the same function.
- Loss of both copies can have significant effects.
- Degradation of one copy can occur without selection pressure resulting in a pseudogene.
Duplication and Specialization
- Mutations can alter the activity or expression of duplicated genes, leading to specialized functions.
- The new gene may have a unique function vital for survival.
- Selection against mutations that eliminate this new function.
Example: Hox Gene Family
- Homeobox transcription factors differentially expressed along the body axis during development.
- They give identity to developing tissues in different parts of the body.
- Different species have varying numbers of Hox clusters: invertebrates have 1, humans have 4, and fish have 7.
Hox Gene Redundancy
- Loss-of-function mutations in Hox genes are lethal in Drosophila but cause subtle effects in humans.
- HOXD13 mutations can result in shortened or fused fingers.
Example: Hyaluronidases
- Enzymes that degrade hyaluronan, a key component of extracellular matrix.
- Nematodes have one hyaluronidase, while humans have two clusters of three paralogues each, with different enzymatic activities and tissue expression patterns.
- Loss of a HYAL gene leads to subtle defects, such as accumulation of hyaluronan and lysosomal storage disorders.
Micro RNAs (miRNAs)
- miRNAs regulate gene expression by binding to target mRNA molecules.
- They are important regulators of gene expression and are involved in various biological processes.
- miRNAs are negative regulators of gene expression, leading to translational repression or mRNA degradation.
- They are implicated in various human diseases.
Bias in Human Genomics Studies
- Most human genetic studies focus on people of European ancestry, leading to a limited understanding of human genetic diversity.
Human Genome Diversity
- African populations have more genetic diversity than any other group.
Summary of RNA Classes
- Different classes of RNA have different functions, such as messenger RNA, ribosomal RNA, transfer RNA, small nuclear RNA, long non-coding RNA, micro RNA, and small nucleolar RNA.
What is a Gene?
- The definition of a gene has broadened, encompassing DNA sequences that encode both proteins and non-coding RNAs.
- Gene boundaries can be difficult to define, as regulatory elements can lie within or even outside of genes.
- Genes can be nested within each other, and multiple genes can be co-transcribed.
Summary of Objectives
- Understanding the content of the human genome, including protein-encoding genes and non-coding RNAs.
- Learning how gene families evolve through duplication events, leading to redundancy, specialization, and pseudogene formation.
- Recognizing the complexities of defining what constitutes a gene.
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Description
Explore the intricacies of the human genome and its complexity compared to other species. Discover how human genes lead to a diverse proteome through various processes like alternative splicing and post-translational modifications. Delve into the genome size differences among species and the significance of gene encoding.
