Multiple Choice
How many chromosomes does a person who is a carrier for familial down syndrome caused by a robertsonian translocation have?
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6. Chromosomal Variation
Chromosomal Rearrangements: Translocations
1:54 minutesProblem 13c
Textbook Question
An animal heterozygous for a reciprocal balanced translocation has the following chromosomes:
MN • OPQRST
MN • OPQRjkl
cdef • ghijkl
cdef • ghiST
Identify the gametes produced by adjacent-1 segregation. Which, if any, of these gametes are viable?
Verified step by step guidance1
Understand the problem: The animal is heterozygous for a reciprocal balanced translocation, meaning two non-homologous chromosomes have exchanged segments. The chromosomes involved are MN • OPQRST, MN • OPQRjkl, cdef • ghijkl, and cdef • ghiST. The task is to identify the gametes produced by adjacent-1 segregation and determine their viability.
Recall the concept of adjacent-1 segregation: In adjacent-1 segregation, homologous centromeres segregate to opposite poles during meiosis. This results in gametes that contain one chromosome from each translocation pair, but these chromosomes are not complementary. This often leads to unbalanced gametes.
Determine the gametes produced: To identify the gametes, pair the chromosomes such that homologous centromeres segregate to opposite poles. For example, one gamete might contain MN • OPQRST and cdef • ghiST, while another might contain MN • OPQRjkl and cdef • ghijkl. Repeat this process to identify all possible combinations.
Assess the viability of the gametes: Viability depends on whether the gametes are balanced or unbalanced. Balanced gametes contain a complete set of genetic information, while unbalanced gametes have duplications or deletions of genetic material. Analyze each gamete to determine if it has duplications or deletions by comparing the segments present in each chromosome.
Conclude the analysis: Summarize which gametes are produced by adjacent-1 segregation and indicate their viability based on the presence or absence of genetic imbalances. Balanced gametes are typically viable, while unbalanced gametes are usually inviable due to missing or extra genetic material.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reciprocal Balanced Translocation
A reciprocal balanced translocation occurs when two chromosomes exchange segments without any loss of genetic material. This results in a rearrangement of genes but maintains the overall genetic balance. In organisms with such translocations, the chromosomes can pair during meiosis, leading to unique segregation patterns that can affect gamete viability.
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Reciprocal Translocation
Adjacent-1 Segregation
Adjacent-1 segregation is a specific way chromosomes can segregate during meiosis in individuals with reciprocal translocations. In this process, one chromosome from each pair of homologous chromosomes is selected, leading to gametes that contain both segments from one translocated chromosome and none from the other. This often results in gametes that are unbalanced and typically non-viable.
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Gamete Viability
Gamete viability refers to the ability of gametes to develop into a viable organism after fertilization. In the context of adjacent-1 segregation, the resulting gametes may have an unbalanced set of chromosomes, which often leads to developmental issues or lethality. Understanding which gametes are viable is crucial for predicting the outcomes of genetic crosses involving translocations.
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