CYTO CHAPTER 3

Cell division and chromosome replication

fundamental biological processes that are essential for growth, reproduction, and maintaining the health of organisms.

Cell division

is the process by which a parent cell divides into two or more daughter cells.

mitosis and meiosis

two main types of cell division

Mitosis

• Purpose: Mitosis is used for growth, repair, and asexual reproduction in eukaryotic organisms

• Process: The cell duplicates its chromosomes and then divides once to produce two genetically identical daughter cells

• Phases: It includes phases such as prophase, metaphase, anaphase, and telophase, followed by cytokinesis (division of the cytoplasm).

Meiosis

• Purpose: Meiosis is used for sexual reproduction and produces gametes (sperm and eggs).

• Process: It involves two rounds of division (meiosis and meiosis Il) and results in four daughter cells, each with half the number of chromosomes of the riginal cell.

• Genetic Variation: includes processes like crossing over and independent assortment, which contribute to genetic diversity.

Chromosome Replication

is part of the cell cycle and occurs during the S phase (synthesis phase) before cell division.

DNA Replication

• Mechanism: Each chromosome's DNA molecule is precisely duplicated. This process involves unwinding the double helix, pairing new nucleotides with each existing strand, and then re-winding to form two double helices.

• Result: This results in two identical copies of each chromosome, known as sister chromatids, connected at a region called the centromere.

Chromosome Segregation in Mitosis

sister chromatids are pulled apart and segregated into two new nuclei during anaphase, ensuring each daughter cell receives an identical set of chromosomes.

Chromosome Segregation in Meiosis

homologous chromosomes (one from each parent) pair up and segregate into different cells in meiosis I, while sister chromatids separate in meiosis Il.

Cell cycle control

a series of checkpoints and proteins that ensure the fidelity and timing of these processes.

DNA helicases, DNA polymerases, and ligases

pray crucial roles in the replication process.

Telomeres

Structures at the ends of chromosomes, ______, protect the DNA and diminish slightly with each replication, playing a role in aging and cancer.

Mitosis

a fundamental process of cell division that results in two genetically identical daughter cells from a single parent cell.

Mitosis

plays a crucial role in growth, repair, and maintenance in multicellular organisms.

Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

Stages of Mitosis

Prophase

Chromosomes condense and become visible under a microscope

Prophase

The mitotic spindle, a structure made of microtubules, starts to form and emanates from the centrosomes

Prometaphase

The nuclear envelope completely breaks down

Prometaphase

Spindle fibers attach to the chromosomes at the centromere, specifically at the kinetochores (protein structures on the centromeres)

Metaphase

Chromosomes, guided by the spindle fibers, align at the metaphase plate (an imaginary line equidistant from the two spindle poles).

Metaphase

this allignment ensures that each daughter cell will receive an identical set of chromosome

Anaphase

The centromeres spit, and the sister chromatids(now individual chromosomes) are pulled apart by the spindle fibers

Anaphase

The chromosomes move toward opposite poles of the cell, ensuring that each new cell will receive one copy of each chromosome

Telophase

The chromosomes reach the opposite poles of the cell and begin to decondense.

Telophase

the nuclear envelope re -forms around each set of chromosomes, and the nucleolus reappears

Telophase

The spindle apparatus disintegrates.

Cytokinesis

often overlaps with telophase

Cytokinesis

The cell's cytoplasm divides, forming two daughter cells.

Mitosis

essential for the growth of an organism from a single fertilized egg into a multicellular adult

Mitosis

plays a crucial role in the repair of tissues (like healing a wound)

Mitosis

continuously replaces cells that are lost due to normal cellular processes or damage, such as skin cells and cells in the gastrointestinal tract lining.

Mitosis

ensures the maintenance of the same chromosome number and genetic material across all somatic cells of an organism.

Mitosis

is a means of asexual reproduction, allowing an individual to reproduce rapidly and independently.

Meiosis

specialized type of cell division that reduces the chromosome number by half

Meiosis

crucial for sexual reproduction and contributes significantly to genetic variation.

Meiosis I and Meiosis II

two consecutive rounds of cell division

Prophase I, Metphase I, Anaphase I, Telophase I and Cytokinesis

Stages of Meiosis I

Synapsis

Chromosomes condense and homologous chromosomes pair up in a process is called

Prophase I

The nuclear envelope breaks down, and the meiotic spindle begins to form.

Prophase I

Crossing over occurs, where non-sister chromatids exchange gentic material, leading to genetic recombination

Metphase I

Tetrads align at the metaphase plate.

Metaphase I

Spindle fibers attach to the centromeres of the homologous chromosomes.

Anaphase I

Homologous chromosomes are pulled to opposite poles of the cell.

Telophase I

Chromosome may decondense slightly and a nuclear envelope may re-form

cytokinesis

the cell divides into two haploid cells during ?

Prophase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis

Stages of Meiosis II

Prophase II

Chromosomes recondense if they had decondensed

Prophase II

The nuclear envelope breaks down again if it had re-formed, and a new spindle forms

Metaphase II

Chromosomes align at the metaphase plate, but unlike meiosis I or mitosis, they are not in homologous pairs

Anaphase II

Sister chromatids are pulled apart to opposite poles of the cell

Telophase Il and Cytokinesis

• Nuclei re-form around the chromosomes.

• Cells divide, resulting in four haploid daughter cells, each genetically distinct

Prophase I

portions of chromatids may break off and attach to adjacent chromatids on the homologous chromosome, a process known as crossing over.

metaphase I

during this phase, the orientation of each homologous pair of chromosomes on the metaphase plate is random.

Meiosis

reduces the chromosome number from diploid to haploid, ensuring that offspring have the same chromosome number as their parents.

Mitosis

During _____, each chromosome is duplicated and the sister chromatids are evenly divided into the two daughter cells. This ensures that each new cell contains the same genetic information as the parent cell.

cancer

Errors in chromosome segregation during mitosis can lead to cells with abnormal numbers of chromosomes, potentially causing diseases such as ______

essential

The faithful replication and distribution of chromosomes are ______ for the growth of an organism and the repair of damaged tissues.

crucial

The consistency in the transmission of genetic information is _______ for maintaining the genetic identity of cells within an organism.

haploid gametes

Meiosis reduces the chromosome number by half, producing _________ from diploid cells.

genetic recombination

Crossing over in prophase I of meiosis leads to ____________, which is the exchange of genetic material between homologous chromosomes. This process creates new combinarions of alleles on each chromosome

Structural Chromosomal Aberrations

deletions, duplications, inversions, and translocations, can have significant genetic implications, including developmental disorders and increased cancer risk.

genetic imprinting

Some genetic disorders are influenced by the parental origin of the chromosome. Ths is due to a phenomenon known as ________, where genes are expressed in a parent-of-origin-specific manner.

parental origin

Some genetic disorders are influenced by the ______ of the chromosome. Ths is due to a phenomenon known as genetic imprinting, where genes are expressed in a parent-of-origin-specific manner.

Nondisjunction, Chromosome Breakage, Faulty Chromosome Replication

3 errors in mitosis

Nondisjunction in Mitosis

Cause: Failure of sister chromatids to separate properly during anaphase of mitosis

Consequence: results in daughter cells with abnormal numbers of chromosomes (aneuploidy), which can lead to developmental disorders and conditions like cancer.

Chromosome Breakage

Cause: Physical or chemical damage, radiation, or errors in DNA replication

Consequence: can lead to cell death or uncontrolled cell division if the damage affects genes regulating the cell cycle.

Cause: errors in dna replication or repair mechanisms

Consequence: May result in mutations, which can be benign or in some cases lead to cancer or othe

Nondisjunction and Abnormal Crossovers

Errors in Meiosis

Nondisjunction in Meiosis

• Cause: Failure of homologous chromosomes or sister chromatids to separate properly during meiosis I or II.

• Consequence: Produces gametes with an abnormal number of chromosomes, leading to disorders like Down syndrome, Turner syndrome, and Klinefelter syndrome.

Abnormal Crossovers

Cause: Improper crossing over during prophase I of meiosis.
Consequence: Can result in deletions, duplications, or translocations of chromosome segments, potentially leading to genetic disorders.