Textbook Question
An animal heterozygous for a reciprocal balanced translocation has the following chromosomes:
MN • OPQRST
MN • OPQRjkl
cdef • ghijkl
cdef • ghiST
Among the three segregation patterns, which is least likely to occur? Why?
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6. Chromosomal Variation
Chromosomal Rearrangements: Translocations
1:28 minutesProblem 13a
Textbook Question
An animal heterozygous for a reciprocal balanced translocation has the following chromosomes:
MN • OPQRST
MN • OPQRjkl
cdef • ghijkl
cdef • ghiST
Diagram the pairing of these chromosomes in prophase I.
Verified step by step guidance1
Identify the chromosomes involved in the reciprocal balanced translocation. In this case, the translocation involves segments of chromosomes MN • OPQRST and cdef • ghijkl, which have exchanged segments to form MN • OPQRjkl and cdef • ghiST.
Understand that during prophase I of meiosis, homologous chromosomes pair up to form a structure called a synaptonemal complex. For a heterozygous reciprocal translocation, this pairing will involve a cross-shaped structure (quadrivalent) due to the rearranged segments.
Diagram the pairing by aligning homologous regions of the chromosomes. Start by pairing MN • OPQRST with MN • OPQRjkl and cdef • ghijkl with cdef • ghiST. Ensure that homologous segments (e.g., OPQRST with OPQRjkl and ghijkl with ghiST) are aligned.
Include the translocated segments in the diagram. For example, the segment 'jkl' from chromosome cdef • ghijkl will pair with its homologous region on MN • OPQRjkl, and the segment 'ST' from MN • OPQRST will pair with its homologous region on cdef • ghiST.
Label the diagram clearly to show the quadrivalent structure formed during prophase I. Indicate the original chromosomes and the translocated segments to highlight the pairing of homologous regions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Heterozygous Reciprocal Balanced Translocation
A heterozygous reciprocal balanced translocation occurs when two non-homologous chromosomes exchange segments, resulting in one chromosome carrying a segment from another. This type of translocation maintains genetic balance, as no genetic material is lost or gained. Understanding this concept is crucial for analyzing how chromosomes pair during meiosis, particularly in prophase I.
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Reciprocal Translocation
Chromosome Pairing in Prophase I
During prophase I of meiosis, homologous chromosomes pair up in a process called synapsis, forming structures known as tetrads. This pairing is essential for genetic recombination and ensures proper segregation of chromosomes. In the context of a heterozygous translocation, the pairing may involve complex interactions between the translocated segments and their homologs.
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07:10Chromosome Structure
Meiotic Recombination
Meiotic recombination is the process by which genetic material is exchanged between homologous chromosomes during prophase I, leading to genetic diversity in gametes. This process can be influenced by structural variations like translocations, which may affect how chromosomes align and exchange segments. Understanding recombination is vital for predicting the genetic outcomes of meiosis in organisms with chromosomal abnormalities.
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