MBG block 2 lecture 4

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Questions and Answers

What is the primary consequence of large chromosomal rearrangements?

They cause minor phenotypic changes.

They may significantly impact viability and phenotype. (correct)

They often lead to infertility.

They have no effect on genome architecture.

Which type of recombination occurs during meiosis between homologous chromosomes?

Interchromosomal Recombination (correct)

Intrachromosomal Recombination

Non-homologous end joining

Homologous recombination

What is the primary outcome of intrachromosomal recombination during DNA repair mechanisms?

Creation of new gene loci through rearrangement.

Uneven exchange of alleles between homologous chromosomes.

Increased genetic diversity.

Restoration of sequence accuracy in sister chromatids. (correct)

What characterizes unbalanced rearrangements in chromosomal structure?

They can result in severe developmental disorders. Signup and view all the answers

Which of the following correctly describes the role of unequal crossing over during homologous recombination?

It results in gene losses or gains, impacting gene dosage. Signup and view all the answers

How does intrachromosomal recombination impact genetic variation?

It typically does not contribute to genetic variation. Signup and view all the answers

What typically happens during sister chromatid exchange when direct repeats misalign?

Causes deletions, duplications, or inversions. Signup and view all the answers

What is the role of fragile sites in chromosome stability?

They are hotspots for chromosome rearrangements. Signup and view all the answers

What effect does recombination between inverted repeats on homologous chromosomes have?

It can create structural rearrangements like inversions. Signup and view all the answers

What is a potential consequence of chromosomal instability often seen in cancer cells related to recombination?

Induction of developmental disorders due to gene copy number variations. Signup and view all the answers

Which mechanism typically leads to chromosome breakage?

Misregulated DNA repair processes Signup and view all the answers

What is a common consequence of haploinsufficiency due to chromosomal rearrangements?

Severe phenotypic changes Signup and view all the answers

Which chromosomal rearrangement does not alter the amount of genetic material?

Inversions Signup and view all the answers

What is the primary consequence of pericentric inversions on chromosome segregation during cell division?

Improper segregation of chromosomes Signup and view all the answers

How does intrachromosomal recombination involving direct repeats affect chromosome architecture?

It excises segments of the chromosome Signup and view all the answers

What is NAHR and what is its consequence for chromosome structure?

Recombination between non-allelic positions leading to various structural rearrangements Signup and view all the answers

What impact do intrachromosomal inversions have on gene function?

They can disrupt genes at inversion breakpoints Signup and view all the answers

What is a potential outcome of having an inversion of an important regulatory region within a chromosome?

Disruption of gene regulation leading to abnormal cell functions Signup and view all the answers

Which mechanism primarily causes chromosomal instability during meiosis?

Improper pairing and recombination of homologous chromosomes Signup and view all the answers

What is one major consequence of genetic deletions caused by intrachromosomal recombination?

Loss of gene function that can lead to diseases Signup and view all the answers

How do inverted repeats on sister chromatids contribute to chromosomal architecture?

They can result in the flipping of segments, creating inversions Signup and view all the answers

What type of structural change does non-allelic homologous recombination primarily result in?

Deletions, duplications, inversions, and translocations Signup and view all the answers

Which structural change occurs during recombination between inverted repeats on the same chromosome?

Creation of intrachromosomal inversions Signup and view all the answers

Which process is primarily involved in the exchange of genetic material between non-homologous chromosomes?

Interchromosomal recombination Signup and view all the answers

What term describes the situation in which one functional allele is inadequate for normal gene function, often leading to disease?

Haploinsufficiency Signup and view all the answers

Which mechanism is most likely to lead to structural abnormalities through random joining of chromosome fragments?

Non-homologous end joining (NHEJ) Signup and view all the answers

What feature increases the likelihood of chromosomal rearrangements due to facilitating misalignment during recombination or repair?

Repetitive sequences Signup and view all the answers

Which type of recombination occurs between similar but non-identical sequences at different loci?

Non-allelic recombination Signup and view all the answers

Which disorder could result from the deletion of a dominant allele, leading to the expression of a normally recessive allele?

Pseudodominance Signup and view all the answers

Which mechanism can lead to structural changes in chromosomes as a result of misalignment during recombination?

Unequal crossing over Signup and view all the answers

Which of the following accurately describes the potential outcome when double-strand breaks (DSBs) are improperly repaired?

Improper repairs can cause deletions, duplications, inversions, or translocations Signup and view all the answers

Which event is characterized by genetic exchanges within sister chromatids on the same chromosome?

Intrachromosomal recombination Signup and view all the answers

What type of chromosomal instability is likely caused by repetitive sequences within the genome?

Increased likelihood of rearrangements Signup and view all the answers

What is a consequence of unbalanced rearrangements in chromosomal architecture?

Alteration of gene dosage leading to developmental abnormalities. Signup and view all the answers

Which mechanism primarily contributes to the occurrence of the Philadelphia chromosome?

Non-homologous recombination between non-homologous chromosomes. Signup and view all the answers

How do balanced rearrangements differ from unbalanced rearrangements in terms of their phenotypic outcomes?

Balanced rearrangements have no net gain or loss of genetic information. Signup and view all the answers

Which of the following is a potential evolutionary impact of chromosomal rearrangements?

Creation of novel genes and new gene combinations. Signup and view all the answers

What role do molecular cytogenetic techniques play in understanding chromosomal rearrangements?

They allow visualization of genetic changes and distinguish rearrangements. Signup and view all the answers

Which genetic condition is associated with the deletion of the 22q11.2 region?

DiGeorge syndrome. Signup and view all the answers

What is a common result of chromosomal instability during mitosis or meiosis?

Development of genetic disorders or infertility. Signup and view all the answers

Which of the following correctly describes haploinsufficiency?

It results from having only one functional copy of a gene. Signup and view all the answers

What is the result of gene dosage effects due to chromosomal rearrangements?

Modified expression potentially leading to developmental issues. Signup and view all the answers

What is the primary mechanism responsible for creating oncogenic fusion proteins in cancers?

Translocations during non-homologous recombination events. Signup and view all the answers

Study Notes

Chromosomal Fragility and Rearrangements

Fragile sites on chromosomes are areas that are especially susceptible to breakage, leading to rearrangements.
Defective DNA repair mechanisms, such as issues with homologous recombination or non-homologous end joining (NHEJ), can hinder proper chromosome repair.

Size of Rearrangement and Genetic Content

Small rearrangements typically have minor phenotypic consequences if they do not disrupt essential genes.
Large rearrangements can severely affect viability and phenotype, causing developmental issues or genetic disorders.
Balanced Rearrangements: No net gain or loss of genetic material, often phenotypically normal but may cause infertility or abnormal offspring due to issues in gametes.
Unbalanced Rearrangements: Result in the gain or loss of genetic material, commonly leading to significant developmental disorders or reduced viability.

Types of Recombination

Interchromosomal Recombination: Occurs during meiosis and facilitates genetic diversity through the exchange of material between homologous chromosomes.
Intrachromosomal Recombination: Involves genetic exchange within sister chromatids; does not generally lead to genetic variation but can cause genomic disorders.
Non-Homologous Recombination: Can occur between non-homologous chromosomes, leading to translocations and rearrangements associated with genetic disorders and cancer, e.g., the Philadelphia chromosome in leukemia.

Contribution to Chromosome Architecture

Alterations in gene dosage due to duplications and deletions can induce overexpression or underexpression of genes, resulting in developmental abnormalities.
Chromosomal instability from rearrangements can disrupt normal chromosome segregation, impacting fertility and contributing to genetic disorders.
Rearrangements can generate new gene combinations, driving evolutionary changes and potentially leading to oncogenesis through translocations and gene fusions.

Balanced vs. Unbalanced Rearrangements

Balanced rearrangements maintain total genetic information but can affect gene expression based on positional effects.
Unbalanced rearrangements result in added or missing genetic material, with effects dependent on the specific genomic regions involved.

Inversions and Recombination

Inversions rearrange gene order without altering the total genetic content; however, they may complicate meiosis and produce abnormal gametes.
Recombination between inverted repeats on sister chromatids can create inversions that disrupt gene function and regulatory mechanisms, possibly affecting chromosome segregation.

Direct Repeats and Recombination

Recombination across direct repeats on homologous chromosomes can induce unequal crossing over, causing duplications and deletions.
Similarly, intrachromosomal recombination between direct repeats on sister chromatids can lead to chromosomal instability, manifesting in cancer.

Non-Allelic Homologous Recombination (NAHR)

Occurs between non-allelic homologous sequences, can lead to structural rearrangements like deletions and duplications, contributing to genomic variability.

Definitions

Haploinsufficiency: A situation where a single functional gene copy is insufficient for normal function, potentially leading to disease.
Pseudodominance: Recessive allele expression due to the deletion of a dominant allele, demonstrating unexpected dominance in phenotypic expression.

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Description

This quiz explores the concepts of chromosomal fragility, including the significance of fragile sites, and the consequences of errors in DNA repair mechanisms. Understanding the correlation between genetic rearrangements and their effects on viability and phenotype is also covered. Test your knowledge on how these factors influence genetic stability.