130 Questions
What is the primary function of mitosis in somatic cells?
To grow, repair, and replace cells
What is the result of meiosis in reproductive cells?
Four daughter cells with half the number of chromosomes as the parent cell
What type of chromosomal mutation involves the gain or loss of one or more chromosomes?
Aneuploidy
What is the normal function of the MYC proto-oncogene?
Regulating cell growth and proliferation
What is the primary consequence of dysregulated apoptosis?
Cancer development and progression
What is the primary purpose of meiosis I in reproductive cells?
To shuffle and recombine genetic material
What is the result of a chromosomal rearrangement?
A change in chromosome structure
What is the function of the HER2 oncogene?
Regulating cell growth and division
What is the primary consequence of aneuploidy?
Disruption of normal cellular function and regulation
What triggers apoptosis in cells?
All of the above
During which stage of the cell cycle do chromosomes condense and become visible?
Prophase
Which type of cell division results in four daughter cells with a unique combination of chromosomes?
Meiosis
What is the result of a chromosomal mutation that increases the number of chromosome sets?
Polyploidy
Which process eliminates damaged cells and prevents tumor formation?
Apoptosis
What type of genes have the potential to cause cancer when activated?
Oncogenes
Which type of chromosomal mutation involves a change in the structure of chromosomes?
Chromosomal rearrangement
What is the result of uncontrolled cell growth and division due to the activation of oncogenes?
Tumor formation
Which type of genetic disorder can result from chromosomal mutations?
All of the above
What is the result of meiosis I in reproductive cells?
Two daughter cells with 23 chromosomes
Which process is important for maintaining tissue homeostasis and preventing cancer?
Apoptosis
What is the result of cytokinesis in somatic cells?
Formation of two daughter cells with identical sets of chromosomes
What type of chromosomal mutation involves the exchange of chromosomal segments?
Translocation
What is the normal function of apoptosis?
To eliminate damaged or unwanted cells
What is the result of oncogene activation?
Uncontrolled cell growth and division
Which type of gene has the potential to cause cancer when mutated or overexpressed?
Oncogene
What is the result of chromosomal mutations?
Cancer or developmental disorders
What is the primary function of apoptosis in development?
To eliminate damaged or unwanted cells
Which type of chromosomal mutation involves the loss of a chromosomal segment?
Deletion
During which stage of mitosis do the sister chromatids separate and move to opposite poles?
Anaphase
What is the primary difference between mitosis and meiosis in terms of the number of daughter cells produced?
Mitosis produces two daughter cells, while meiosis produces four
What type of chromosomal mutation involves the rearrangement of chromosomes, leading to changes in gene expression?
Translocation
Which process is triggered by the activation of pro-apoptotic genes, leading to the elimination of damaged cells?
Apoptosis
What is the primary function of oncogenes in normal cellular function?
Regulation of cell growth and division
Which type of chromosomal mutation involves the loss of one or more chromosomes, leading to changes in gene expression?
Monosomy
What is the result of uncontrolled cell growth and division due to the activation of oncogenes?
Cancer
What is the critical difference between the number of daughter cells produced in mitosis and meiosis, and how does this relate to the purpose of each process?
Mitosis produces 2 daughter cells with the same number of chromosomes as the parent cell, ensuring genetic continuity, whereas meiosis produces 4 daughter cells with half the number of chromosomes as the parent cell, ensuring genetic diversity.
Describe the potential consequences of aneuploidy, and how this type of chromosomal mutation can lead to the development of cancer.
Aneuploidy can lead to uncontrolled cell growth, genetic instability, and increased susceptibility to further mutations, increasing the risk of cancer development.
Explain how oncogenes contribute to the development of cancer, and provide examples of specific oncogenes.
Oncogenes, such as HER2, RAS, and MYC, can cause uncontrolled cell growth and division when mutated or overexpressed, contributing to cancer development. normally involved in cell growth and division.
Describe the critical role of apoptosis in maintaining tissue homeostasis and preventing cancer, and explain how dysregulation of apoptosis can contribute to cancer development.
Apoptosis eliminates damaged or unwanted cells, maintaining tissue homeostasis, while dysregulation of apoptosis can allow damaged cells to persist, contributing to cancer development.
Compare and contrast the stages of mitosis and meiosis, highlighting the key differences between the two processes.
Mitosis consists of four stages (prophase, metaphase, anaphase, and telophase), resulting in two daughter cells with the same number of chromosomes, while meiosis consists of two consecutive cell divisions (meiosis I and meiosis II), resulting in four daughter cells with half the number of chromosomes.
Explain how chromosomal mutations can lead to the development of cancer, and describe the different types of chromosomal mutations that can occur.
Chromosomal mutations, such as aneuploidy, translocations, deletions, insertions, and inversions, can disrupt normal cellular function, leading to uncontrolled cell growth and division, and increasing the risk of cancer development.
Describe the role of mitosis in maintaining genetic continuity, and explain how errors during mitosis can lead to chromosomal mutations.
Mitosis ensures genetic continuity by replicating DNA and dividing it evenly between daughter cells, while errors during mitosis can result in chromosomal mutations, such as aneuploidy or translocations.
Explain how the process of meiosis contributes to genetic diversity, and describe the importance of crossing over in this process.
Meiosis shuffles and recombines genetic material during crossing over, increasing genetic diversity, and ensuring that each gamete receives a unique combination of chromosomes.
Describe the normal function of the HER2 oncogene, and explain how its activation can contribute to cancer development.
HER2 is normally involved in cell growth and division, but its overexpression or mutation can lead to uncontrolled cell growth and division, contributing to cancer development.
Explain the importance of apoptosis in eliminating damaged cells and preventing tumor formation, and describe the consequences of dysregulated apoptosis.
Apoptosis eliminates damaged or unwanted cells, preventing tumor formation, while dysregulation of apoptosis can allow damaged cells to persist, contributing to cancer development.
During which phase of the cell cycle does the cyclin level rise and then fall abruptly?
M phase
What is the result of a cell not receiving a go-ahead signal at the G2 checkpoint?
The cell enters the G0 phase
What is the function of MPF (Maturation-Promoting Factor) in the cell cycle?
To trigger the cell's passage past the G2 checkpoint
What is the state of most cells in the human body?
G0 phase
What is the role of cyclin-dependent kinases in the cell cycle?
To regulate the progression of the cell cycle
Which cells are incapable of re-entering the cell cycle from the G0 phase?
Nerve cells
What is the primary function of the cyclin-Cdk complex known as MPF in animal cells?
To trigger the events of mitosis
During which phase of the cell cycle do cyclins accumulate and associate with Cdk molecules?
G2 phase
What is the result of a cell lacking an essential nutrient in the culture medium?
Cell division is inhibited
What is the role of cyclin-dependent kinases (Cdks) in the cell cycle?
To phosphorylate proteins and initiate mitosis
What is the purpose of the G2 checkpoint in the cell cycle?
To ensure that the cell is ready to enter mitosis
What is the result of the association of cyclins with Cdk molecules during the G2 phase?
The triggering of the events of mitosis
What is the primary characteristic of the G1 phase in animal cells?
The cell spends most of its time doing its job in the organism
What is the significance of the G0 phase in multicellular organisms?
It is a stage where cells are quiescent and not dividing
During which stage of the cell cycle do the centrosomes duplicate and move apart?
Interphase
What is the significance of the aster in the spindle?
It is a radial array of short microtubules
What is the primary function of the spindle microtubules during mitosis?
To move chromosomes to the poles
What is the primary function of the centrosome in animal cells?
To organize the cell's microtubules during mitosis
During which stage of the cell cycle do the centrosomes move apart and the spindle microtubules grow out?
Prometaphase
During which phase of the cell cycle does the cell prepare for cell division?
G2 phase
What is the approximate duration of the M phase in a 24-hour cell cycle?
Less than 1 hour
What is the role of centrioles in the formation of the spindle microtubules during mitosis?
Not essential, and they can be destroyed with a laser microbeam without affecting the formation of the spindle
What is the approximate duration of the G1 phase in a 24-hour cell cycle?
5-6 hours
What is the role of the spindle microtubules during mitosis?
To separate the sister chromatids during mitosis
What is the approximate duration of the S phase in a 24-hour cell cycle?
10-12 hours
What is the primary difference between meiosis I and mitosis during metaphase?
The alignment of pairs of homologous chromosomes on the metaphase plate
What is the function of cohesins during meiosis I?
To attach sister chromatids along their lengths
What occurs during synapsis in prophase I of meiosis?
The pairing of replicated homologs along their lengths by the synaptonemal complex
What is the result of crossing over during meiosis I?
Genetic rearrangement between nonsister chromatids
During which stage of meiosis I do the replicated chromosomes of each homologous pair move toward opposite poles?
Anaphase I
What is unique to meiosis I compared to mitosis?
The occurrence of synapsis and crossing over
What is a fundamental feature shared by the three types of sexual life cycles?
The contribution to genetic variation among offspring
Why can only diploid cells undergo meiosis?
Because haploid cells have a single set of chromosomes that cannot be further reduced
What is the result of meiosis I in terms of chromosome separation?
Homologous chromosomes separate
What is the purpose of sister chromatid cohesion in meiosis?
To hold sister chromatids together until they are separated
How many daughter cells are produced at the end of meiosis, and how many chromosomes do they have?
Four daughter cells with a haploid number of chromosomes
What is the key difference between meiosis and mitosis in terms of the number of chromosome sets?
Meiosis reduces the number of chromosome sets, while mitosis conserves them
What is the primary function of shugoshin in meiosis I?
To protect cohesins from cleavage at the centromere
What is the outcome of meiosis I in terms of the number of chromosome sets?
The number of chromosome sets is halved
What is the mechanism responsible for separating sister chromatids in meiosis II and mitosis?
Cohesin cleavage at the centromere
What is the primary source of genetic diversity?
Mutations
What is the primary consequence of the behavior of chromosomes during meiosis and fertilization?
The production of offspring with a unique combination of chromosomes
What is the role of meiosis in generating genetic variation?
To produce genetic variation through the shuffling of alleles
What is the consequence of independent assortment of chromosomes during meiosis I?
A 50% chance of receiving a maternal or paternal chromosome
How many possible combinations of chromosomes are there in humans during meiosis?
223
What is the result of crossing over during meiosis I?
Recombinant chromosomes with genes from both parents
Why is crossing over essential in meiosis I?
To facilitate the alignment of homologous chromosomes during metaphase I
What is the average number of crossing over events per chromosome pair in humans?
One to three times
What is the role of chiasmata in meiosis I?
To hold homologs together as the spindle forms
What is the result of independent assortment of chromosomes during meiosis I in terms of genetic variability?
Increased genetic variability
What is the significance of sister chromatid cohesion in meiosis I?
Sister chromatid cohesion ensures that the sister chromatids remain associated all along their length, allowing them to separate properly during meiosis II.
How does meiosis II differ from mitosis in terms of the number of daughter cells produced?
Meiosis II produces four haploid daughter cells, whereas mitosis produces two diploid daughter cells.
What is the purpose of meiosis I in the context of genetic variation?
Meiosis I increases genetic variation among offspring by separating homologous chromosomes, allowing for shuffling of alleles.
Compare and contrast the function of meiosis I and meiosis II in the production of gametes.
Meiosis I separates homologous chromosomes, while meiosis II separates sister chromatids, resulting in four haploid gametes.
How does the process of meiosis contribute to the reduction of chromosome sets from diploid to haploid?
Meiosis halves the number of chromosome sets from diploid to haploid through two consecutive cell divisions.
What is the significance of the haploid number of chromosomes in the production of gametes?
The haploid number of chromosomes ensures that fertilization of gametes results in a diploid zygote with the correct number of chromosomes.
What is the key difference between meiosis I and meiosis II in terms of the number of chromosome sets?
Meiosis I halves the number of chromosome sets from two (diploid) to one (haploid), whereas meiosis II is an equational division.
What is the role of shugoshin in meiosis I?
Shugoshin protects cohesins from cleavage at the centromere during meiosis I, keeping the sister chromatids joined.
How does the mechanism of separating sister chromatids differ between meiosis II and mitosis?
There is no difference in the mechanism of separating sister chromatids between meiosis II and mitosis.
What is the primary source of genetic diversity in a population?
Mutations are the original source of genetic diversity.
What is the main mechanism responsible for most of the genetic variation that arises in each generation?
The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation.
What are the three mechanisms that contribute to genetic variation arising from sexual reproduction?
Independent assortment of chromosomes, crossing over, and random fertilization.
What is the significance of synapsis and crossing over during prophase I of meiosis, and how does it differ from mitosis?
Synapsis and crossing over occur during prophase I of meiosis, where replicated homologs pair up and become physically connected, leading to genetic rearrangement between nonsister chromatids. This process does not occur during mitosis, resulting in genetically identical daughter cells.
Describe the alignment of homologs on the metaphase plate during meiosis I, and how it differs from mitosis.
During meiosis I, pairs of homologous chromosomes line up on the metaphase plate, whereas in mitosis, individual chromosomes line up. This unique alignment in meiosis I allows for the separation of homologs during anaphase I.
What is the significance of cohesins in meiosis I, and how do they differ from mitosis?
Cohesins are protein complexes that hold sister chromatids together during meiosis I. In contrast, enzymes remove cohesins in mitosis, allowing sister chromatids to separate. Meiosis I releases cohesins in two steps, ensuring the separation of homologs during anaphase I.
What is the outcome of anaphase I in meiosis, and how does it differ from anaphase in mitosis?
During anaphase I of meiosis, the replicated chromosomes of each homologous pair move toward opposite poles, while the sister chromatids of each replicated chromosome remain attached. In contrast, during anaphase of mitosis, the sister chromatids separate.
What is the primary difference between meiosis I and meiosis II in terms of the separation of chromosomes?
Meiosis I involves the separation of homologs, whereas meiosis II involves the separation of sister chromatids. This results in the production of four haploid daughter cells with unique combinations of chromosomes.
How does the separation of homologs during meiosis I contribute to genetic diversity, and what is the significance of crossing over in this process?
The separation of homologs during meiosis I allows for the shuffling of genetic material, increasing genetic diversity. Crossing over during prophase I of meiosis I further increases genetic diversity by introducing new combinations of alleles.
What is the significance of the random orientation of homologous pairs of chromosomes at the metaphase plate during meiosis I?
It contributes to genetic variability due to the independent assortment of chromosomes.
What is the mathematical expression that represents the number of possible combinations of chromosomes when they assort independently into gametes?
2n, where n is the haploid number of the organism.
What is the average number of crossing over events that occur per chromosome pair in humans?
One to three times per chromosome pair.
What is the role of chiasmata in meiosis I?
They hold homologous chromosomes together as the spindle forms.
How do crossing over events result in recombinant chromosomes?
Homologous portions of two nonsister chromatids trade places, resulting in individual chromosomes carrying genes derived from two different parents.
What is the significance of independent assortment of chromosomes during meiosis I?
It results in a unique combination of chromosomes in each daughter cell.
What is the relationship between the number of possible combinations of chromosomes and the haploid number of an organism?
The number of possible combinations is 2n, where n is the haploid number of the organism.
Match the stage of meiosis with the correct description:
Meiosis I = Separates homologous chromosomes. Meiosis II = Separates sister chromatids. Interphase = Replication of chromosomes to form sister chromatids Mitosis = Conserves the number of chromosome sets
Match the term with its correct definition:
Sister chromatid cohesion = The association of sister chromatids along their length. Homologous chromosomes = A pair of chromosomes inherited from different parents. Diploid = A cell with a single set of chromosomes. Haploid = A cell with two sets of chromosomes.
Match the process with its correct result:
Meiosis = Four daughter cells with half the number of chromosomes as the parent cell. Mitosis = Two daughter cells with the same number of chromosomes as the parent cell. Meiosis I = Separation of homologous chromosomes. Meiosis II = Separation of sister chromatids.
Match the characteristic with the correct type of cell division:
Halves the number of chromosome sets = Meiosis Conserves the number of chromosome sets = Mitosis Produces four daughter cells = Meiosis Produces two daughter cells = Mitosis
Match the stage of meiosis with the correct event:
Meiosis I = Sister chromatids remain together. Meiosis II = Sister chromatids separate. Interphase = Chromosomes condense and become visible. Mitosis = Chromosomes condense and become visible.
Match the term with its correct description:
Diploid = A cell with two sets of chromosomes. Haploid = A cell with a single set of chromosomes. Mitosis = Cell division that conserves the number of chromosome sets. Meiosis = Cell division that halves the number of chromosome sets.
Match the process with its correct purpose:
Meiosis = To produce gametes with unique combinations of chromosomes. Mitosis = To produce somatic cells with the same number of chromosomes as the parent cell. Meiosis I = To separate homologous chromosomes. Meiosis II = To separate sister chromatids.
Match the stage of meiosis with the correct result:
Meiosis I = Two daughter cells with paired homologous chromosomes. Meiosis II = Four daughter cells with half the number of chromosomes as the parent cell. Interphase = Replicated chromosomes with sister chromatids. Mitosis = Two daughter cells with the same number of chromosomes as the parent cell.
Match the characteristic with the correct type of cell division:
Produces gametes = Meiosis Produces somatic cells = Mitosis Halves the number of chromosome sets = Meiosis Conserves the number of chromosome sets = Mitosis
Match the term with its correct description:
Homologous chromosomes = Chromosomes that are alike in structure and function. Sister chromatids = Genetically identical chromosomes that are closely associated. Diploid = A cell with one set of chromosomes. Haploid = A cell with two sets of chromosomes.
Study Notes
Cellular Reproduction and Cancer
Mitosis
- Process of cell division that results in two daughter cells identical to the parent cell
- Consists of four stages: prophase, metaphase, anaphase, telophase
- Occurs in somatic cells (non-reproductive cells) for growth, repair, and replacement
- Ensures genetic continuity by maintaining the same number of chromosomes (46 in humans)
Meiosis
- Process of cell division that results in four daughter cells with half the number of chromosomes as the parent cell
- Occurs in reproductive cells (gametes) for sexual reproduction
- Consists of two successive cell divisions (meiosis I and meiosis II)
- Ensures genetic diversity by shuffling and recombining genetic material
Chromosomal Mutations
- Changes in the number or structure of chromosomes
- Types:
- Aneuploidy: gain or loss of one or more chromosomes
- Polyploidy: increase in the number of chromosome sets
- Chromosomal rearrangements: changes in chromosome structure (e.g. deletions, duplications, translocations)
- Can lead to cancer by disrupting normal cellular function and regulation
Oncogenes
- Genes that have the potential to cause cancer when mutated or overexpressed
- Normally involved in cell growth and division, but can become tumorigenic when altered
- Examples:
- HER2 (human epidermal growth factor receptor 2)
- MYC (proto-oncogene that regulates cell growth and proliferation)
- RAS (proto-oncogene involved in cell signaling pathways)
Apoptosis
- Process of programmed cell death
- Essential for maintaining tissue homeostasis and preventing cancer
- Can be triggered by DNA damage, cellular stress, or other signals
- Dysregulation of apoptosis can contribute to cancer development and progression
Cellular Reproduction and Cancer
Mitosis
- Results in two daughter cells identical to the parent cell
- Consists of four stages: prophase, metaphase, anaphase, telophase
- Occurs in somatic cells (non-reproductive cells) for growth, repair, and replacement
- Ensures genetic continuity by maintaining 46 chromosomes in humans
Meiosis
- Results in four daughter cells with half the number of chromosomes as the parent cell
- Occurs in reproductive cells (gametes) for sexual reproduction
- Consists of two successive cell divisions (meiosis I and meiosis II)
- Ensures genetic diversity by shuffling and recombining genetic material
Chromosomal Mutations
- Changes in the number or structure of chromosomes
- Aneuploidy: gain or loss of one or more chromosomes
- Polyploidy: increase in the number of chromosome sets
- Chromosomal rearrangements: changes in chromosome structure (e.g. deletions, duplications, translocations)
- Can lead to cancer by disrupting normal cellular function and regulation
Oncogenes
- Genes that have the potential to cause cancer when mutated or overexpressed
- Normally involved in cell growth and division
- Examples: HER2, MYC, RAS
- Can become tumorigenic when altered
Apoptosis
- Process of programmed cell death
- Essential for maintaining tissue homeostasis and preventing cancer
- Triggered by DNA damage, cellular stress, or other signals
- Dysregulation of apoptosis contributes to cancer development and progression
Cellular Reproduction and Cancer
Mitosis
- Mitosis is a type of cell division that produces two daughter cells identical to the parent cell
- Occurs in somatic cells (non-reproductive cells)
- Consists of four stages: prophase, metaphase, anaphase, and telophase
- Results in 2 daughter cells with 46 chromosomes (diploid)
Meiosis
- Meiosis is a type of cell division that produces four daughter cells with half the number of chromosomes as the parent cell
- Occurs in reproductive cells (gametes)
- Consists of two consecutive cell divisions: meiosis I and meiosis II
- Results in 4 daughter cells with 23 chromosomes (haploid)
Chromosomal Mutations
- Changes in the number or structure of chromosomes can lead to genetic disorders and cancer
- Types of chromosomal mutations include:
- Aneuploidy: gain or loss of one or more chromosomes
- Polyploidy: increase in the number of chromosome sets
- Chromosomal rearrangements: changes in the structure of chromosomes
Apoptosis
- Apoptosis is a process of programmed cell death
- Mechanism to eliminate damaged or unwanted cells
- Involves a series of biochemical events leading to cell death
- Important for maintaining tissue homeostasis and preventing cancer
Oncogenes
- Oncogenes are genes that have the potential to cause cancer
- Normally involved in cell growth and division
- Can become activated through mutations, leading to uncontrolled cell growth and tumor formation
- Examples of oncogenes include HER2, RAS, and MYC
Cellular Reproduction and Cancer
Mitosis
- Mitosis is the process of cell division that results in two daughter cells with the same number of chromosomes as the parent cell
- It occurs in somatic cells (non-reproductive cells) and involves six phases: interphase, prophase, metaphase, anaphase, telophase, and cytokinesis
- During interphase, the cell grows, replicates its DNA, and prepares for cell division
Meiosis
- Meiosis is the process of cell division that results in four daughter cells with half the number of chromosomes as the parent cell
- It occurs in reproductive cells (gametes: sperm and egg cells) and involves two successive cell divisions (meiosis I and meiosis II)
- Meiosis I involves the pairing and separation of homologous chromosomes, while meiosis II involves the separation of sister chromatids
Chromosomal Mutations
- Chromosomal mutations are changes in the number or structure of chromosomes
- Types of chromosomal mutations include aneuploidy, translocation, deletion, and duplication
- Chromosomal mutations can lead to cancer or developmental disorders, such as Down syndrome
Apoptosis
- Apoptosis is programmed cell death, a natural process to eliminate damaged or unwanted cells
- It is regulated by genes and signaling pathways and is important for development, tissue homeostasis, and prevention of cancer
- Dysregulation of apoptosis can contribute to cancer development
Oncogenes
- Oncogenes are genes that have the potential to cause cancer when mutated or overexpressed
- They are normally involved in cell growth, division, and survival
- Examples of oncogenes include HER2, RAS, and MYC
- Oncogene activation can lead to uncontrolled cell growth and cancer development
Cellular Reproduction
- Mitosis is a type of cell division that results in two daughter cells with the same number of chromosomes as the parent cell, occurring in somatic cells.
- Mitosis consists of four stages: prophase, metaphase, anaphase, and telophase, ensuring genetic continuity by replicating DNA and dividing it evenly between daughter cells.
Meiosis
- Meiosis is a type of cell division that results in four daughter cells with half the number of chromosomes as the parent cell, occurring in reproductive cells (gametes: sperm and egg cells).
- Meiosis consists of two consecutive cell divisions: meiosis I and meiosis II, ensuring genetic diversity by shuffling and recombining genetic material during crossing over.
Chromosomal Mutations
- Chromosomal mutations can occur spontaneously or as a result of environmental factors (e.g., radiation, chemicals).
- Types of chromosomal mutations include:
- Aneuploidy: abnormal number of chromosomes.
- Translocation: exchange of genetic material between non-homologous chromosomes.
- Deletion: loss of genetic material.
- Insertion: addition of genetic material.
- Inversion: reversal of genetic material.
Oncogenes
- Oncogenes are genes that have the potential to cause cancer when mutated or overexpressed.
- Normally, oncogenes are involved in cell growth and division.
- Oncogenes can become cancer-causing through mutations, gene amplification, or chromosomal translocation.
- Examples of oncogenes include HER2, RAS, and MYC.
Apoptosis
- Apoptosis is a process of programmed cell death that eliminates damaged or unwanted cells to maintain tissue homeostasis.
- Apoptosis involves a series of biochemical events that lead to cell death.
- Dysregulation of apoptosis can contribute to cancer development and progression.
- Apoptosis can be triggered by various stimuli, including DNA damage, oxidative stress, and activation of pro-apoptotic genes.
Cell Cycle Regulation
- The cell cycle consists of three phases: G1, S, and G2, followed by M phase (mitosis)
- Most cells in the human body are in the G0 phase, which is a non-dividing state
- Liver cells and muscle cells can re-enter the cell cycle from G0 phase
- Nerve cells and mature cells never divide
G1 Phase
- G1 phase is the most variable in length in different cell types
- Cells in G1 phase perform their specific functions in the organism (e.g., nerve cells carry impulses)
S Phase
- S phase is where DNA replication occurs
- Chapter 16 will cover DNA synthesis
G2 Phase
- G2 phase prepares the cell for cell division
- Cyclin-dependent kinases (Cdks) control the cell cycle
- MPF (maturation-promoting factor) is a complex of cyclin and Cdk that acts as a go-ahead signal at the G2 checkpoint
M Phase
- M phase includes prophase, prometaphase, metaphase, anaphase, and telophase
- MPF triggers the cell's passage past the G2 checkpoint into M phase
- Cyclin level rises during S and G2 phases, then falls abruptly during M phase
Molecular Mechanisms
- MPF phosphorylates proteins, initiating mitosis
- MPF contributes to chromosome condensation and spindle formation during prophase
Centrosome and Spindle Formation
- Centrosome duplicates during interphase, forming two centrosomes
- Centrosomes move apart during prophase and prometaphase
- Spindle microtubules grow out from centrosomes
- An aster, a radial array of short microtubules, extends from each centrosome
External Factors Influencing Cell Division
- External factors, such as nutrients and growth factors, can influence cell division
- Cells fail to divide if an essential nutrient is lacking
- Most mammalian cells divide in culture only if the growth medium includes specific growth factors
Meiosis vs. Mitosis
- Meiosis produces cells that differ genetically from the parent cell and from each other, while mitosis produces daughter cells that are genetically identical to the parent cell and to each other.
Unique Events of Meiosis I
- Synapsis and crossing over occur during prophase I, where replicated homologs pair up and become physically connected along their lengths by the synaptonemal complex.
- Crossing over is a genetic rearrangement between nonsister chromatids that occurs during synapsis.
- Chiasmata (X-shaped regions) hold homologs together after synapsis.
- Alignment of homologs on the metaphase plate occurs during metaphase I, where pairs of homologous chromosomes line up on the metaphase plate.
- Separation of homologs occurs during anaphase I, where the replicated chromosomes of each homologous pair move toward opposite poles.
Chromosome Behavior in Meiosis
- Sister chromatids are attached along their lengths by protein complexes called cohesins.
- Cohesin cleavage is released in two steps: along the arms in anaphase I, and at the centromeres in anaphase II.
- Shugoshin protein protects cohesins from cleavage at the centromere during meiosis I.
Meiosis I and II
- Meiosis I is a reductional division, halving the number of chromosome sets from two (diploid) to one (haploid).
- Meiosis II is an equational division, where sister chromatids separate.
Genetic Variation
- Mutations are the original source of genetic diversity.
- Reshuffling of alleles during meiosis and fertilization produces offspring with unique sets of traits.
- Three mechanisms contribute to genetic variation: independent assortment of chromosomes, crossing over, and random fertilization.
Life Cycles
- Only diploid cells can undergo meiosis, while haploid cells can divide by mitosis.
- The three types of sexual life cycles differ in the timing of meiosis and fertilization, but all contribute to genetic variation among offspring.
Chromosome Halving and Doubling
- Meiosis reduces the number of chromosome sets from diploid to haploid.
- The four daughter cells at the end of meiosis have only half as many chromosomes as the original parent cell.
Meiosis vs. Mitosis
- Meiosis produces cells that differ genetically from the parent cell and from each other, while mitosis produces daughter cells that are genetically identical to the parent cell and to each other.
Unique Events of Meiosis I
- Synapsis and crossing over occur during prophase I, where replicated homologs pair up and become physically connected along their lengths by the synaptonemal complex.
- Crossing over is a genetic rearrangement between nonsister chromatids that occurs during synapsis.
- Chiasmata (X-shaped regions) hold homologs together after synapsis.
- Alignment of homologs on the metaphase plate occurs during metaphase I, where pairs of homologous chromosomes line up on the metaphase plate.
- Separation of homologs occurs during anaphase I, where the replicated chromosomes of each homologous pair move toward opposite poles.
Chromosome Behavior in Meiosis
- Sister chromatids are attached along their lengths by protein complexes called cohesins.
- Cohesin cleavage is released in two steps: along the arms in anaphase I, and at the centromeres in anaphase II.
- Shugoshin protein protects cohesins from cleavage at the centromere during meiosis I.
Meiosis I and II
- Meiosis I is a reductional division, halving the number of chromosome sets from two (diploid) to one (haploid).
- Meiosis II is an equational division, where sister chromatids separate.
Genetic Variation
- Mutations are the original source of genetic diversity.
- Reshuffling of alleles during meiosis and fertilization produces offspring with unique sets of traits.
- Three mechanisms contribute to genetic variation: independent assortment of chromosomes, crossing over, and random fertilization.
Life Cycles
- Only diploid cells can undergo meiosis, while haploid cells can divide by mitosis.
- The three types of sexual life cycles differ in the timing of meiosis and fertilization, but all contribute to genetic variation among offspring.
Chromosome Halving and Doubling
- Meiosis reduces the number of chromosome sets from diploid to haploid.
- The four daughter cells at the end of meiosis have only half as many chromosomes as the original parent cell.
Meiosis vs Mitosis
- Meiosis produces cells that differ genetically from the parent cell and from each other, while mitosis produces daughter cells that are genetically identical to the parent cell and to each other.
Unique Events in Meiosis I
- Synapsis and crossing over: replicated homologs pair up and become physically connected along their lengths by a zipper-like protein structure called the synaptonemal complex, and genetic rearrangement between nonsister chromatids occurs during this stage.
- Alignment of homologs on the metaphase plate: pairs of homologous chromosomes line up on the metaphase plate.
- Separation of homologs: replicated chromosomes of each homologous pair move toward opposite poles, while sister chromatids of each replicated chromosome remain attached.
Sister Chromatid Cohesion in Meiosis
- Sister chromatids are attached along their lengths by protein complexes called cohesins.
- In meiosis, sister chromatid cohesion is released in two steps: in metaphase I, homologs are held together by cohesion between sister chromatid arms, and in anaphase I, cohesins are cleaved along the arms, allowing homologs to separate.
Shugoshin and Cohesin Cleavage
- A protein named "shugoshin" (Japanese for "guardian spirit") protects cohesins from cleavage at the centromere during meiosis I, keeping the sister chromatids joined.
Meiosis I and II
- Meiosis I is a reductional division that halves the number of chromosome sets from two (diploid) to one (haploid).
- Meiosis II is an equational division.
- The mechanism for separating sister chromatids is virtually identical in both meiosis II and mitosis.
Genetic Variation in Sexual Life Cycles
- Mutations are the original source of genetic diversity.
- Reshuffling of alleles during meiosis and fertilization produce offspring with their own unique set of traits.
- Three mechanisms contribute to genetic variation arising from sexual reproduction: independent assortment of chromosomes, crossing over, and random fertilization.
Meiosis and Fertilization
- Only diploid cells can undergo meiosis because haploid cells have a single set of chromosomes that cannot be further reduced.
- Each cycle of chromosome halving and doubling contributes to genetic variation among offspring.
Learn about the processes of mitosis and meiosis, including their stages, functions, and importance in maintaining genetic continuity.
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