Multiple Choice
Inversions cause what type of chromosomal rearrangement?
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6. Chromosomal Variation
Chromosomal Rearrangements: Overview
2:04 minutesProblem 9
Textbook Question
Predict how the synaptic configurations of homologous pairs of chromosomes might appear when one member is normal and the other member has sustained a deletion or duplication.
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Understand the concept of homologous chromosomes: Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci but may have different alleles. Synapsis occurs during meiosis when homologous chromosomes pair up to form a structure called a bivalent.
Consider the impact of a deletion: A deletion is a loss of a segment of DNA from one chromosome. During synapsis, the chromosome with the deletion will have a shorter sequence compared to its homologous partner. This mismatch can lead to the formation of a loop or bulge in the normal chromosome to compensate for the missing segment.
Consider the impact of a duplication: A duplication is an extra copy of a segment of DNA on one chromosome. During synapsis, the chromosome with the duplication will have an extra sequence compared to its homologous partner. This mismatch can lead to the formation of a loop or bulge in the duplicated chromosome to accommodate the extra segment.
Visualize the synaptic configuration: In the case of a deletion, the normal chromosome may form an unpaired loop to align with the shorter chromosome. In the case of a duplication, the duplicated chromosome may form an unpaired loop to align with the normal chromosome. These loops are visible under a microscope during meiosis and are indicative of structural abnormalities.
Relate this to genetic consequences: The presence of deletions or duplications can affect gene dosage and lead to phenotypic abnormalities. Understanding synaptic configurations helps predict how these structural changes might impact genetic inheritance and expression during meiosis.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Homologous Chromosomes
Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same structure and gene sequence, one inherited from each parent. They carry genes for the same traits but may have different alleles. Understanding their structure is crucial for predicting how genetic variations, such as deletions or duplications, affect synaptic configurations during meiosis.
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Chromosome Structure
Chromosomal Deletion and Duplication
Chromosomal deletion refers to the loss of a segment of a chromosome, while duplication involves the repetition of a segment. These structural changes can lead to significant genetic imbalances, affecting gene dosage and expression. In the context of homologous chromosomes, these alterations can disrupt normal pairing and synapsis during meiosis, leading to potential fertility issues or genetic disorders.
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04:18Duplications
Synapsis and Crossing Over
Synapsis is the process during meiosis where homologous chromosomes pair up and align closely, allowing for genetic recombination through crossing over. This process is essential for genetic diversity but can be affected by structural abnormalities like deletions or duplications. When one chromosome is altered, it may not align properly with its homolog, impacting the exchange of genetic material and the overall genetic outcome.
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