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Questions and Answers
What do homologous chromosomes share regarding genetic information?
During which phase of the cell cycle do chromosomes duplicate?
What is a primary consequence of cells continuing to divide beyond their programmed limits?
How are the alleles on homologous chromosomes different?
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Which type of chromosomes do humans have an even number of?
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Which cell cycle phase allows for cell growth and preparation for mitosis?
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What genetic condition results from an abnormal number of chromosomes?
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What occurs during the mitotic phase of the cell cycle?
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What is metabolism primarily responsible for in living organisms?
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Which principle explains why energy transformations in living cells are similar to those in non-living systems?
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What best describes selective barriers in biological systems?
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What is the primary function of homeostasis in living organisms?
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Why do living things reproduce?
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Which characteristic of life involves the ability to grow towards stimuli like light and gravity?
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Which of the following statements is true regarding living cells?
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What type of reproduction involves offspring that resemble the parent but may not be genetically identical?
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How many chromosomes are considered to be present despite the duplication during the process?
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During which phase of mitosis do the chromosomes align along the metaphase plate?
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What is primarily responsible for the movement of sister chromatids during anaphase?
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What forms during cytokinesis in animal cells to facilitate cell division?
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Which event marks the end of the mitotic phase?
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What significant change occurs during telophase?
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What distinguishes cytokinesis in plant cells from that in animal cells?
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What does the G2 phase ensure before the mitotic process begins?
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What is the process called that allows genetic variation during meiosis?
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During which phase do homologous chromosomes line up on the metaphase plate?
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How many times can crossing over typically occur for one homologous pair during meiosis?
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What is the ploidy of the cells that result from telophase 1 and cytokinesis?
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Which of the following statements is true regarding metaphase 2?
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What is the result of sexual fertilization involving two 1n gametes?
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During which phase of meiosis does crossing over occur?
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How many daughter cells are formed at the end of meiosis?
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What happens during Anaphase 1 of meiosis?
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What is the effect of DNA proofreading during replication?
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Which of the following best describes the outcome of meiosis II?
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After which phase do animal cells stop dividing following meiosis?
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In organisms that may reproduce both sexually and asexually, what action can occur after meiosis?
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Study Notes
Properties of Life
- Metabolism involves the transformation of matter and energy within organisms, similar to processes in non-living systems.
- Energy transformations abide by the laws of thermodynamics, applicable both inside and outside living organisms.
- Life emerges from complex interactions among non-living parts rather than a mysterious force.
- Living organisms demonstrate self-movement and growth, such as plants growing towards light.
- Selective barriers, like cellular membranes, regulate the exchange of substances between the internal and external environments.
Homeostasis
- Homeostasis is the ability of an organism to maintain stable internal conditions despite external fluctuation.
- An example is the consistent body temperature in humans regardless of the ambient temperature.
- Life can be defined as metabolic processes occurring within selective barriers.
Responsiveness to Stimuli
- Living organisms respond to external stimuli, exemplified by plants adjusting their growth toward water and light sources.
Reproduction
- Reproduction can be asexual or sexual; offspring usually resemble but are not identical to parents.
- Genetic traits are transmitted via DNA, organized into chromosomes.
- Humans possess 46 chromosomes in 23 homologous pairs, with each chromosome carrying alleles for specific traits.
Cell Division: Mitosis and Meiosis
- Mitosis produces two genetically identical daughter cells, crucial for growth and repair.
- The cell cycle consists of interphase (G1, S, G2) and the mitotic phase (prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis).
- In interphase:
- G1: Cell growth and preparation for DNA replication. Some cells enter a resting phase (G0).
- S: DNA synthesis where chromosomes duplicate into sister chromatids.
- G2: Final preparations for mitosis; checks for errors in replication.
Stages of Mitosis
- Prophase: Chromatin condenses into visible chromosomes; spindle fibers form.
- Prometaphase: Nuclear envelope breaks; spindle fibers attach to chromosomes.
- Metaphase: Chromosomes align at the metaphase plate; spindle fibers are fully formed.
- Anaphase: Sister chromatids are pulled apart by spindle fibers.
- Telophase: Chromosomes uncoil, nuclear envelopes reform around them.
- Cytokinesis: Cytoplasm divides, forming two distinct daughter cells.
Meiosis
- Meiosis results in four haploid cells from one diploid cell, creating genetic diversity through crossing over and separation of homologous chromosomes.
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Meiosis I:
- Prophase I: Crossing over occurs; homologous chromosomes pair.
- Metaphase I: Homologous pairs line up at the metaphase plate.
- Anaphase I: Homologous chromosomes are pulled apart; chromatids remain attached.
- Telophase I and Cytokinesis: Two haploid cells are formed.
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Meiosis II: Similar to mitosis, separates sister chromatids without further DNA replication.
- Prophase II: No chromosome duplication occurs.
- Metaphase II: Chromosomes align at the metaphase plate.
- Anaphase II: Sister chromatids are pulled apart.
- Telophase II and Cytokinesis: Four haploid daughter cells are produced.
Genetic Variability
- Genetic diversity is crucial for species evolution; arises from meiotic processes like crossing over and independent assortment.
- DNA replication involves the separation of strands and synthesis of complementary nucleotides, with proofing mechanisms to ensure accuracy.
Summary of Meiosis
- Starts with diploid cells and results in haploid daughter cells through two meiotic divisions.
- Crossing over occurs in Prophase I, enhancing genetic variability.
- Meiosis contributes to the formation of gametes, which fuse to create a diploid zygote upon fertilization.
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