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Questions and Answers
What is the significance of crossing-over during prophase I?
What is the significance of crossing-over during prophase I?
- It leads to the production of identical cells.
- It prevents separation of sister chromatids.
- It enhances genetic variation among the offspring. (correct)
- It causes chromosomes to line up at the equator.
In which stage of meiosis do homologous chromosomes separate?
In which stage of meiosis do homologous chromosomes separate?
- Metaphase I
- Anaphase I (correct)
- Telophase II
- Prophase II
How many nuclei are formed at the end of telophase II?
How many nuclei are formed at the end of telophase II?
- Four (correct)
- Five
- Three
- Two
What is the main difference between meiosis I and meiosis II?
What is the main difference between meiosis I and meiosis II?
What is the chromosome number in starting cells before meiosis begins?
What is the chromosome number in starting cells before meiosis begins?
What is the primary purpose of meiosis in sexually reproducing organisms?
What is the primary purpose of meiosis in sexually reproducing organisms?
How many chromosomes do human gametes contain after meiosis?
How many chromosomes do human gametes contain after meiosis?
During which phase of meiosis does crossing over occur?
During which phase of meiosis does crossing over occur?
What happens to the number of chromosomes during meiosis?
What happens to the number of chromosomes during meiosis?
Which statement about chromatids after DNA duplication is true?
Which statement about chromatids after DNA duplication is true?
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Study Notes
Meiosis Overview
- Meiosis generates genetic diversity and produces gametes (sperm and egg cells) with 23 chromosomes each.
- Compared to mitosis, which creates identical body cells, meiosis involves reduction division resulting in half the chromosome number.
Chromosome Numbers
- Sperm and egg cells each have 23 chromosomes; when fused during fertilization, they form a zygote with 46 chromosomes, necessary for human development.
- Chromosomes are counted based on centromere numbers; even after DNA duplication, chromosomes remain counted as 46.
- Chromatid numbers increase post-duplication, crucial for understanding meiotic processes.
Meiosis Phases
- Meiosis is a two-step process consisting of Meiosis I and Meiosis II, involving distinct stages like prophase, metaphase, anaphase, telophase, and cytokinesis.
- Meiosis I includes:
- Prophase I: Homologous chromosomes pair and exchange genetic material (crossing over).
- Metaphase I: Chromosome pairs align at the cell equator.
- Anaphase I: Homologous chromosomes separate.
- Telophase I: Formation of two nuclei occurs, followed by cytokinesis.
Meiosis II
- Meiosis II involves:
- Prophase II: Chromosomes do not pair, and crossing over does not happen.
- Metaphase II: Chromosomes line up individually at the equator.
- Anaphase II: Sister chromatids are pulled apart.
- Telophase II: Leads to four new nuclei, concluding with cytokinesis.
Genetic Variation
- Homologous chromosomes are similar in size and gene type and are vital during recombination.
- Crossing over creates recombinant chromosomes, enhancing genetic variety among gametes.
- Independent assortment during meiosis also contributes to genetic diversity.
Implications
- Meiosis generates diverse gametes, leading to variation in offspring, critical for evolution and adaptability.
- Errors in chromosome separation during meiosis can result in genetic disorders, highlighting the importance of accurate chromosome segregation.
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