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Questions and Answers
What is the haploid number of chromosomes in humans?
What is the process that reduces chromosome number from diploid to haploid?
What happens during prophase I of meiosis?
What is the name for the physical manifestation of crossing over in meiosis?
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What determines an individual's sex in humans?
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During which phase of meiosis do homologous chromosomes pair up in a process called synapsis?
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Which event is unique to meiosis and does not occur in mitosis?
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What is the result of meiosis II?
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What separates during anaphase I of meiosis?
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During anaphase I of meiosis, sister chromatids separate and are carried to opposite poles of the cell.
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The haploid number of chromosomes in humans is 46.
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In meiosis, chromosomes replicate once followed by one cell division, resulting in two daughter cells.
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Meiosis produces daughter cells that are genetically identical to each other.
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During the second meiotic division, the processes are virtually identical to those of mitosis.
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During cytokinesis, the cytoplasm divides to form two daughter cells.
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Chromosomes are formed from a condensed, coiled and folded chromatin.
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During meiosis, the division process forms two daughter nuclei.
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Study Notes
Cell Division and the Cell Cycle
- Cell division is the process by which a cell becomes two daughter cells, and it is essential for the continuity of life.
- The cell cycle consists of three stages: interphase, mitosis, and cytokinesis.
Interphase
- Interphase is the longest stage of the cell cycle, accounting for 90% of the cycle.
- It consists of three sub-phases:
- G1 phase: the cell carries out its everyday activities.
- S phase: genetic material replicates itself, allowing the cell to contain enough material for two cells upon division.
- G2 phase: cellular organelles are produced to allow for an adequate amount for the new cell being produced.
Mitosis
- Mitosis is the division process that forms two daughter nuclei.
- It consists of five sub-phases:
- Prophase: the chromosomes are tightly coiled, with sister chromatids joined together.
- Prometaphase: the nuclear envelope fragments, and microtubules from one pole attach to one of two kinetochores.
- Metaphase: the spindle fibers push the sister chromatids until they are all arranged at the imaginary plane equidistant between the poles.
- Anaphase: the centromeres divide, resulting in the separation of the sister chromatids.
- Telophase: the cell continues to elongate, and two nuclei begin to form.
Cytokinesis
- Cytokinesis is the division of the cytoplasm, which typically follows mitosis.
- It involves the contraction of the cell, which pinches the cell into two new cells.
Chromosomes and DNA
- A cell's genetic information is packaged as DNA.
- In eukaryotes, the genome consists of several DNA molecules.
- Each chromosome has hundreds or thousands of genes, which specify an organism's inherited characters.
- Chromatin is a DNA-protein complex that is organized into a long thin fiber.
- Chromatids are two sister arms formed from each duplicated chromosome, containing identical copies of the chromosome's DNA.
Meiosis
- Meiosis is a division process that occurs in the gonads, yielding four daughter cells, each with half the number of chromosomes of the parent cell.
- In humans, meiosis reduces the number of chromosomes from 46 to 23.
- Each person inherits 23 chromosomes from each parent, one set in an egg and one set in a sperm during meiosis.
Fertilization
- Fertilization fuses two gametes together, doubling the number of chromosomes to 46 again.
- The fertilized egg undergoes trillions of cycles of mitosis and cytokinesis to produce a fully developed multicellular human.### Mitosis
- The mitotic spindle forms, pushing centrosomes away from each other towards opposite ends (poles) of the cell.
Stages of Mitosis
- Prometaphase: Nuclear envelope fragments, and microtubules from one pole attach to one kinetochore, while microtubules from the other pole attach to the other kinetochore.
- Metaphase: Spindle fibers push sister chromatids until they are all arranged at the imaginary plane equidistant between the poles.
- Anaphase: Centromeres divide, separating sister chromatids, and each is pulled towards the pole to which it is attached by spindle fibers.
- Telophase: Two nuclei begin to form, surrounded by the fragments of the parent's nuclear envelope, and chromatin becomes less tightly coiled.
Cytokinesis
- Cytokinesis: Division of the cytoplasm that typically follows mitosis.
- Cytokinesis process: Contraction of the cell pinches the cell into two new cells.
Cell Cycle
- Interphase: Cell growth and preparation for cell division.
- Mitosis: Division of the nucleus into two daughter nuclei.
- Cytokinesis: Division of the cytoplasm.
Life Cycle
- Life cycle: Generation-to-generation sequence of stages in an organism's reproductive history, starting from conception to producing its own offspring.
Chromosomes
- Human somatic cells: Have 46 chromosomes, arranged in 23 pairs of homologous chromosomes.
- Karyotype: Display of the 46 chromosomes, showing 23 pairs of chromosomes with the same length, centromere position, and staining pattern.
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Description
Discover the process of cell division and the role it plays in the continuity of life. From unicellular organisms to the development of multicellular organisms, delve into the significance of the cell cycle in the reproduction of cells.
