Questions and Answers
Which phase of prophase I is characterized by the formation of bivalents?
What occurs during the pachytene stage of prophase I?
In which prophase I phase do chiasmata become visible?
What distinguishes the diakinesis stage of prophase I?
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Which of the following is an enzyme involved in crossing over during prophase I?
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What happens to the synaptonemal complex during diplotene?
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In which stage of prophase I does chromosome visibility first begin to increase?
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How long can the diplotene stage last in oocytes of some vertebrates?
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Study Notes
Prophase I Overview
- Prophase I is longer and more complex than mitotic prophase.
- It is divided into five stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
Leptotene
- Chromosomes begin to become visible under a light microscope.
- Gradual compaction of chromosomes occurs during this phase.
Zygotene
- Chromosomes pair together through a process called synapsis.
- Paired chromosomes are known as homologous chromosomes.
- Formation of the synaptonemal complex occurs, which is essential for pairing.
- Paired homologous chromosomes are referred to as bivalents or tetrads.
Pachytene
- Distinct appearance of four chromatids per bivalent, clearly visible as tetrads.
- Crossing over occurs at recombination nodules, allowing genetic material exchange between non-sister chromatids.
- The enzyme recombinase facilitates the crossing-over process.
- Recombination is completed by the end of this stage, with chromosomes linked at crossover sites.
Diplotene
- Begins with the dissolution of the synaptonemal complex.
- Homologous chromosomes start to separate at most points, except at crossover sites forming X-shaped structures called chiasmata.
- In some vertebrates, diplotene can last for extended periods, including months or years.
Diakinesis
- Marked by the terminalisation of chiasmata, indicating preparation for separation.
- Chromosomes become fully condensed, and the meiotic spindle assembles.
- Nucleolus disappears and nuclear envelope breaks down, transitioning into metaphase.
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Description
This quiz explores Prophase I, the first stage of meiosis, emphasizing its complexity compared to mitosis. Learn about the five sub-phases: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis, and how chromosomal behavior varies during this critical stage.
