Biology Chapter: Mitosis and Chromosome Structure

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Questions and Answers

What role do spindle fibers play during mitosis?

They initiate cytokinesis.

They condense chromatin into chromosomes.

They replicate DNA molecules.

They attach to centromeres of chromosomes. (correct)

Which phase of the cell cycle is primarily characterized by chromosomal replication?

G2 Phase

M Phase

G1 Phase

S Phase (correct)

Which statement accurately describes interphase?

Chromosomes are visible under a light microscope in interphase.

Interphase consists of three phases: G1, S, and G2. (correct)

Cells are completely inactive during interphase.

Mitosis occurs during interphase.

What is the approximate duration of the mitosis phase in an ideal animal cell?

1 hour Signup and view all the answers

What happens during the G2 phase of interphase?

Chromosomes begin to condense and prepare for mitosis. Signup and view all the answers

Which statement about the cell cycle is true regarding the time spent in various phases?

G1 is typically the longest phase. Signup and view all the answers

During which phase of the cell cycle does a cell become committed to complete the cycle?

G1 Phase Signup and view all the answers

What initiates the formation of the mitotic apparatus in animal cells?

Centrioles reproducing in the cytoplasm. Signup and view all the answers

What structural change occurs to chromatids during late prophase?

They condense and become highly organized. Signup and view all the answers

What is the primary function of the spindle fibers during metaphase?

To pull chromatids towards the poles of the cell. Signup and view all the answers

What happens to the centromeres during anaphase?

They separate, allowing sister chromatids to move apart. Signup and view all the answers

Which statement about plant cells is correct regarding their structure during mitosis?

They lack centrioles, relying on other structures during mitosis. Signup and view all the answers

What is NOT a characteristic of telophase?

The spindle fibers are still present. Signup and view all the answers

How does colchicine affect mitosis?

It prevents the separation of sister chromatids. Signup and view all the answers

What determines the shape of moving chromosomes during anaphase?

The position of the centromere. Signup and view all the answers

What process occurs immediately after the physical separation of sister chromatids?

Cytoplasmic division through cleavage. Signup and view all the answers

What is the diploid number of chromosomes for humans?

46 chromosomes Signup and view all the answers

What distinguishes a homologous chromosome from a chromatid?

Homologous chromosomes are non-identical but paired, while chromatids are identical halves of a replicated chromosome. Signup and view all the answers

Which of the following statements about mitosis is true?

Mitosis results in two genetically identical daughter cells. Signup and view all the answers

What role do histones play in chromosome structure?

They condense DNA into chromatin structures. Signup and view all the answers

What is the function of the centromere in a chromosome?

It serves as the attachment point for spindle fibers during mitosis. Signup and view all the answers

How does meiosis differ from mitosis in terms of chromosome number in the daughter cells?

Meiosis produces haploid daughter cells, while mitosis produces diploid cells. Signup and view all the answers

Why is it significant that chromosomes are located in homologous pairs in eukaryotic somatic cells?

It provides genetic diversity through the mixing of genetic information during meiosis. Signup and view all the answers

What would happen if a cell did not undergo mitosis properly?

The daughter cells would not be genetically identical. Signup and view all the answers

During which stage of meiosis do homologous chromosomes undergo synapsis?

Prophase I Signup and view all the answers

What is the result of crossing over during Prophase I of meiosis?

Genetic variation Signup and view all the answers

How does the chromosome number change from Meiosis I to Meiosis II?

Remains the same throughout Signup and view all the answers

What is a characteristic feature of Metaphase I in meiosis compared to mitosis?

Homologous chromosomes pair side by side Signup and view all the answers

Which stage of meiosis results in the formation of four haploid cells?

Meiosis II Signup and view all the answers

What is meant by a 'bivalent' in the context of meiosis?

Two homologous chromosomes paired together Signup and view all the answers

Which statement accurately describes cytokinesis in plant cells during telophase?

It is supplemented by the formation of a cell plate Signup and view all the answers

What describes the chromosome number before and after meiosis?

It reduces to a quarter of the original number Signup and view all the answers

What characterizes Prophase I in meiosis?

Chromosomes condense and tetrads form. Signup and view all the answers

During which stage does independent assortment occur?

Metaphase I Signup and view all the answers

What is a key distinction between anaphase I of meiosis and anaphase of mitosis?

Centromeres do not separate in anaphase I. Signup and view all the answers

Which phase follows telophase I in meiosis?

Interkinesis Signup and view all the answers

What occurs during Anaphase II of meiosis?

Sister chromatids migrate to opposite poles. Signup and view all the answers

The formation of tetrads during meiosis occurs in which sub-stage of Prophase I?

Zygonema Signup and view all the answers

Which error can lead to genetic aberrations during meiosis?

Failure of homologous chromosomes to disjoin. Signup and view all the answers

How does Metaphase I of meiosis differ from mitotic metaphase?

Homologous chromosomes are paired during metaphase I. Signup and view all the answers

Study Notes

Chromosome Morphology

Chromosomes are thread-like structures composed of DNA and proteins.
DNA is associated with proteins, forming a complex called chromatin.
Histones are proteins that help organize DNA into nucleosomes.
Centromeres are constricted regions of the chromosome that divide it into two arms.
The shorter arm is called the p arm, and the longer arm is called the q arm.
All chromosomes other than sex chromosomes are autosomes.

Mitosis

Mitosis is a form of cell division where one cell produces two daughter cells, each with an identical set of chromosomes.
Spindle fibers from centrioles attach to centromeres.
Chromosomes are copied, and the two copies are called chromatids.
Chromatids are held together by the centromere until separation.

The Cell Cycle

Mitosis is a phase within the cell cycle, which also includes interphase.
Interphase consists of three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).
During interphase, cells grow, produce proteins and organelles.
Chromosomes replicate during the S phase.
The G2 phase prepares the cell for mitosis, with chromosomes beginning to condense.

Stages of Mitosis

The process of mitosis is designated as the M phase and divided into four stages: prophase, metaphase, anaphase, and telophase.
During prophase, replicated chromosomes condense, becoming visible under a light microscope.
The nuclear membrane and nucleolus disappear.
The mitotic apparatus consisting of asters and spindle fibers forms.
Late prophase is the best stage to count chromosomes as they are highly condensed and not confined within a nuclear membrane.
Metaphase begins when replicated chromosomes line up at the center of the cell, called the spindle equator or metaphase plate.
The centromeres are connected to spindle fibers, holding the chromatids together.
Anaphase begins when sister chromatids separate at the centromere and move to opposite poles of the cell.
Telophase involves the reformation of the nuclear membrane around each daughter nucleus, the reappearance of the nucleolus, and the breakdown of spindle fibers.

Meiosis

Meiosis is a specialized two-stage cell division that reduces the chromosome number from diploid (2n) to haploid (n).
It involves a single DNA replication and two divisions of the cytoplasm.
Meiosis I is a reductional division where a diploid cell produces two diploid cells.
Meiosis II is an equational division, similar to mitosis, where sister chromatids are separated.
During prophase I, replicated chromosomes thicken and condense, and homologous chromosomes pair up in a process called synapsis.
Synapsis forms a bivalent (two chromosomes) or tetrad (four chromatids).
Crossing over, the exchange of genetic material between non-sister chromatids, can occur during prophase I.
Metaphase I involves homologous chromosomes (bivalents) aligning randomly on the metaphase plate.
Anaphase I involves the separation of homologous chromosomes, with centromeres not dividing, resulting in two haploid daughter cells.
Telophase I involves the formation of a nuclear membrane around each daughter nucleus and cytokinesis, dividing the cell into two haploid daughter cells.

Meiosis II

Prophase II is brief and involves chromosomes recondensing and the formation of spindle fibers.
Metaphase II involves chromosomes aligning at the metaphase plate with each centromere attached to spindle fibers.
Anaphase II involves centromere division and sister chromatids separating.
Telophase II involves nuclear membrane reformation and division of the cytoplasm, resulting in four haploid daughter cells.

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Explore the intricate processes of cell division and chromosome organization in this quiz. From the structure of chromosomes to the stages of mitosis and the cell cycle, test your knowledge on these fundamental biology concepts.