When does recombination occur in meiosis

Genetic screens have revealed mutants of yeast and Drosophila that block pairing of homologous chromosomes. These are also defective in recombination. Likewise, mutants defective in some aspects of recombination are also defective in pairing. Indeed, the process of synapsis or pairing between homologous chromosomes in zygotene, crossing over between homologs in pachytene, and resolution of the crossovers in the latter phases of meiosis I diakinesis, metaphase I, and anaphase I correspond to the synapsis, formation of a recombinant joint and resolution that mark the progression of recombination, as will be explained below.

Ross C. Hardison , T. Exercise 8. Possible Answers: Metaphase I. Correct answer: Prophase I. Explanation : During prophase I homologous chromosomes will line up with one another, forming tetrads. Report an Error. What is the evolutionary purpose of cells that undergo crossing over? Possible Answers: To produce gametes that are genetically identical.

Correct answer: To increase genetic diversity. Explanation : Crossing over is a process that happens between homologous chromosomes in order to increase genetic diversity. Example Question 3 : Understanding Crossing Over. During which step of cell division does crossing over occur? Possible Answers: Metaphase II. Explanation : When chromatids "cross over," homologous chromosomes trade pieces of genetic material, resulting in novel combinations of alleles, though the same genes are still present.

Example Question 4 : Understanding Crossing Over. What structures exchange genetic material during crossing over? Possible Answers: Egg and sperm chromosomes. Correct answer: Nonsister chromatids. Explanation : During crossing over, homologous chromosomes come together in order to form a tetrad. Example Question 5 : Understanding Crossing Over.

Crossover of homologous chromosomes in meiosis occurs during which phase? Possible Answers: Prophase II of meiosis. Correct answer: Prophase I of meiosis. Explanation : The crossing over of homologous chromosomes occurs in prophase I of meiosis.

Example Question 6 : Understanding Crossing Over. During crossing over, two homologous chromosomes pair to form which of the following choices? Possible Answers: Tetrad. Correct answer: Tetrad. Explanation : The tetrad, which divides into non-sister chromatids, exchanges genetic information in order to make the genetic pool more variant, and result in combinations of phenotypic traits that can occur outside of linked genotypic coding.

In contrast, the approach taken by Lee et al. They found that sites of RCOs, and therefore the initial sites of spontaneous damage, were nonrandomly distributed. Furthermore, the authors uncovered evidence for the existence of one region with elevated RCOs. This is exceptionally interesting because it represents a region prone to spontaneous rather than induced DSBs. It will be exciting to see if other such hotspots for spontaneous damage and mitotic recombination exist, and what role they play in genome stability.

Taking advantage of the flexibility of the assay used by Lee et al. Many questions concerning mitotic recombination remain to be answered. Perhaps the most basic of these is what makes certain regions more prone to mitotic breakage and recombination than others? The approach of Lee et al. These and other studies of mitotic recombination, a process both fundamental and far reaching, promise to continue to provide interesting insights into causes of genome instability.

The authors have declared that no competing interests exist. National Center for Biotechnology Information , U. PLoS Genet. Published online Mar Matthew C. Gregory P. Copenhaver, Editor. Author information Copyright and License information Disclaimer. Copyright LaFave, Sekelsky. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

See the article on page e This article has been cited by other articles in PMC. Open in a separate window. Recombination in meiosis. Further Exploration Concept Links for further exploration meiosis DNA chromosome gene linkage principle of independent assortment eukaryote nucleus gamete haploid recombination frequency Principles of Inheritance.

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