Chapter 7: Mitosis & Meiosis
Phenotype: observable characteristic of physical feature
Chromosomes: threadlike structures containing proteins and nucleic acids
Sister chromatids: duplicated and sister chromosome
Centromere: chromatids attached to a center point
Homologous chromosomes: sister chromatids separate, carry alleles
Mitosis: cell division in somatic cells, which produces daughter cells with exact replicas of the parents DNA
Somatic cells: the body’s non-reproductive cells, two sets of chromosomes
Meiosis: cell division in germ cells, produces daughter cells with DNA that is a combination of the DNA of the two parent cells. Resulting gametes are the body’s reproductive cells, which have half the genetic material that somatic has
reproduction: unicellular organism reproduce through cell division
growth: organisms get larger through cell division
regeneration: some organisms can regenerate entire body parts through mitosis
asexual reproduction: offspring identical to parent
binary fission: single celled prokaryotes reproduce through this simple process
asexual is favorable when: there are not many available mates
con: low genetic diversity
sexual reproduction: two individuals contribute half of their genetic material to the offspring
gametes formed through meiosis
meiosis: haploid cells
combine to produce diploid zygote in fertilization
meiosis: process of cell division resulting in daughter cells with half of the original cell’s genetic material
Diplontic Life Cycle (animals):
merger of two haploid (1n) gametes in fertilization, produces a diploid (2n) organism
to reproduce, organism reproduces gametes through mitosis
in diplontic, dominant multicellular organism is diploid
Haplontic Life Cycle (protists, fungi, algae):
merger of haploid gametes in fertilization, produces a diploid (2n) zygote
zygote undergoes meiosis to form haploid cells called spores
haploid cells grow and divide mitotically to form haploid multicellular organism
Fungi: can alternate between sexual (to survive with harsh environments) and asexual (to spread quickly)
in haplontic, dominant multicellular organism is haploid
Signal to Initiate - some external or internal signal initiates asexual reproduction (environmental)
DNA replication - all cellular organisms have DNA-based genomes, which are replicated and passed on to daughter cells
2 regions in circular prokaryotic chromosome:
ori: origin of replication
ter: terminus of replication
Segregation of DNA - DNA replication begins at the center of the cell, daughter DNA strand separates, ori regions move toward separate sides of the cell
Cytokinesis - cytoplasm is split and two daughter cells result
Chromosome number: number of chromosomes it has in total
Ploidy: number of homologous chromosomes that exists for each chromosome type
haploid (1n): only one chromosome for each chromosome type; human gametes
diploid (2n): two homologous chromosomes for each chromosome type; human somatic cells
Sister chromatids: two chromatids joined together at a common centromere
Centromere: region of chromosomes to which microtubules attach during cell division; has protein kinetochores = chromosome movement
Homologous chromosomes: in diploid organisms, chromosomes exist in homologous pairs
Nucleus: surrounded by membrane and contains DNA
Dna packaged by special proteins to form a complex called chromatin
Interphase: DNA is stretched out
Nucleolus: specialized structure in nucleus, synthesis of ribosomal RNA and assembly of rRNA into ribosomes
Centrosomes: regions near the nucleus that are associated with spindle fibers, organizing center for microtubules in the cell, site of synthesis and replication of microtubules
Centrioles: within centrosomes, pair of hollow microtubule rings in animals
Cytoskeleton: internal scaffolding, constructed of filaments, structure and mechanical support, dynamic
Signal to divide - growth factor initiates cell division (internal signal)
Replication of DNA - DNA replication occurs during the S-phase
Segregation of DNA - each daughter cells must have one copy of each chromosome, segregate into two new nuclei through mitosis
Cytokinesis - division of the cell into two daughter cells, plants: cell wall, animal: membrane
Interphase: mitosis is not occurring, cell synthesizes RNA, produces proteins, grows in size, nucleus and nucleolus visible, DNA replication occurs
Gap 1 (G1): cell grows, produces protein and RNA, prepares for protein synthesis, cells get stuck (G0)
Synthesis (S): DNA is duplicated through DNA replication upon the receipt of a proper signal
Gap 2 (G2): cell grows, produces proteins, microtubules, in prep for mitosis
Mitotic (M): parent cell divides into two daughter cells
mitosis: orderly division of the nucleus
cytokinesis: division of the cytoplasm
prophase: nucleolus fades, chromatin → chromosomes, microtubules disassemble, mitotic spindle forms
prometaphase: nuclear envelope is completely dissolved and some spindle fibers attach at the kinetochores
metaphase: chromosomes align at center
anaphase: chromatids pull apart, move to cell poles, spindle fibers shorten, cell elongates
telophase: spindle breaks down, nuclear envelopes and nucleoli re-form, chromosomes uncoil and become less compact
animals: formation of contractile ring of actin and myosin filaments along the metaphase plate
plants: occurs as vesicles from golgi move along microtubules, forming a cell plate membrane
G1 checkpoint: DNA synthesis will be delayed if DNA is damaged, will not continue again until the DNA has been repaired. this checkpoint reduces deleterious effects of DNA damage
S-phase checkpoint: DNA synthesis will be delayed if the DNA is damaged or if replication is incomplete
G2 checkpoint: the cell will not progress from the G2 phase to mitosis unless the DNA is undamaged and intact
M-phase checkpoint: cell will not go into anaphase unless chromosomes are properly aligned along the metaphase plate and kinetochores are attached to the spindle fibers. this checkpoint ensures the cell is ready for division before it proceeds any further
Regulation of the cell cycle is controlled by proteins called cyclins and cyclin-dependent kinases (CDKs)
kinase; phosphorylating enzyme
CDK binds to cyclin → allosteric change exposes active site on CDK → CDK phosphorylates proteins that regulate CDK cycle
every CDK has a specific cyclin that activates it, so cells can precisely control CDK activity by controlling the production and breakdown of cyclins
cyclins are produced in response to various signals, including presence of growth factors
sexual reproduction: combination of haploid gametes from two parents → diploid
Prophase I:
synaptonemal protein complex attaches homologs together, forming a tetrad/bivalent, with 2 homologous chromosomes and four homologous chromatids
synapsis: fusion of chromosome pairs
crossing over: DNA is exchanged between homologs at chiasmata = recombinant chromatids, increases genetic variation
spindle fibers form and attach to kinetochores
synaptonemal complex begins to break down and nuclear envelope breaks down
Metaphase I:
chromosomes line up along metaphase plate in homologous pairs
spindles from each pole attach to one chromosome of each pair
independent assortment
Anaphase I:
homologous chromosomes of each tetrad separate and move along the spindle fibers toward each pole as the kinetochore tubules shorten
Telophase I and Cytokinesis:
homologous chromosomes reach opposite poles
microtubules disappear
new nuclear membrane surrounds each haploid set
chromosomes uncoil
cytokinesis (pinching of cell membrane) completes creation of 2 daughter cells
sister chromatids separate, cells further divide into four haploid daughter cells with a single chromosome each
Prophase II:
chromosomes condense, spindle forms, chromosomes move toward metaphase plate
Metaphase II:
chromosomes meet at the metaphase plate, spindle fibers of each pole attach to the kinetochores of the sister chromatids
Anaphase II:
centromeres of the sister chromatids separate
sister chromatids move toward opposite poles
sister chromatids are now called chromosomes
Telophase II and Cytokinesis:
splitting of the cell into two daughter cells, chromosomes uncoil
total of four haploid gametes are formed
Mitosis: process of nuclear division in eukaryotic cells that conserves the chromosome number by equally allocating replicated chromosomes to each of the daughter nuclei
Meiosis: two-stage type of cell division in sexually reproducing organisms that results in four cells with half the chromosome number of the original number of the original cell
Event | Mitosis | Meiosis |
---|---|---|
DNA Replication | Interphase (S) | Interphase (S) |
# of Cell Divisions | 1 | 2 |
Number of Daughter Cells | 2 | 4 |
Ploidy of Daughters | 2n (diploid) | 1n (haploid) |
Synapsis of Homologs | no | yes (early prophase I) |
Crossing over/Recombination | no | yes (late prophase I) |
Biological purpose | duplicating cells | generating gametes |
Males: spermatogenesis, generate gametes throughout their lives, prophase I lasts 1 week
Females: born with all oogonia, prophase I begins before birth, meiotic process stops until puberty
Recombination: genetic variation
Independent Assortment: during meiosis I, the chromosomes line up in a random fashion along the metaphase plate
Crossing Over: prophase I of meiosis 1, crossing over of chromosomes occurs
Nondisjunction: occurs when homologous pairs fail to separate in anaphase I, or sister chromatids fail to separate in anaphase II
Aneuploidy: chromosomal abnormality in which a person has an abnormal number of chromosomes in his or her genome
Monosomy: one chromosome lacks a homologous partner
almost always lethal
turner syndrome: nonlethal, only one X chromosome
Trisomy: three copies of one chromosome type
trisomy 16: most common, miscarriage
trisomy 21 (down syndrome): 3 copies of 21st chromosome
Polyploidy: abnormal amount of chromosome sets
can result from an extra round of DNA replication before meiosis or lack of spindle formation in meiosis in II
most common: triploidy (3n) or tetraploidy (4n)
Translocation: occurs when there is a crossover between nonhomologous chromosomes
Apoptosis: programmed cell death
detach from neighbors, break chromatin apart into small pieces, form blebs: membranous lobes that break into fragments
remains are ingested by surrounding cells in phagocytosis
external signals: lack of mitotic signal
internal signals: recognition of damaged DNA
Cancer: disease caused by uncontrolled cell division of abnormal cells in the body
oncogene proteins (positive regulators): positively regulate the cell cycle in cancer cells, cause cells to progress through cell cycle more quickly → higher than normal cell division
tumor suppressors (negative regulators): negatively regulate the cell cycle in normal cells, slow the process of cell division down → inactive in cancer cells
Phenotype: observable characteristic of physical feature
Chromosomes: threadlike structures containing proteins and nucleic acids
Sister chromatids: duplicated and sister chromosome
Centromere: chromatids attached to a center point
Homologous chromosomes: sister chromatids separate, carry alleles
Mitosis: cell division in somatic cells, which produces daughter cells with exact replicas of the parents DNA
Somatic cells: the body’s non-reproductive cells, two sets of chromosomes
Meiosis: cell division in germ cells, produces daughter cells with DNA that is a combination of the DNA of the two parent cells. Resulting gametes are the body’s reproductive cells, which have half the genetic material that somatic has
reproduction: unicellular organism reproduce through cell division
growth: organisms get larger through cell division
regeneration: some organisms can regenerate entire body parts through mitosis
asexual reproduction: offspring identical to parent
binary fission: single celled prokaryotes reproduce through this simple process
asexual is favorable when: there are not many available mates
con: low genetic diversity
sexual reproduction: two individuals contribute half of their genetic material to the offspring
gametes formed through meiosis
meiosis: haploid cells
combine to produce diploid zygote in fertilization
meiosis: process of cell division resulting in daughter cells with half of the original cell’s genetic material
Diplontic Life Cycle (animals):
merger of two haploid (1n) gametes in fertilization, produces a diploid (2n) organism
to reproduce, organism reproduces gametes through mitosis
in diplontic, dominant multicellular organism is diploid
Haplontic Life Cycle (protists, fungi, algae):
merger of haploid gametes in fertilization, produces a diploid (2n) zygote
zygote undergoes meiosis to form haploid cells called spores
haploid cells grow and divide mitotically to form haploid multicellular organism
Fungi: can alternate between sexual (to survive with harsh environments) and asexual (to spread quickly)
in haplontic, dominant multicellular organism is haploid
Signal to Initiate - some external or internal signal initiates asexual reproduction (environmental)
DNA replication - all cellular organisms have DNA-based genomes, which are replicated and passed on to daughter cells
2 regions in circular prokaryotic chromosome:
ori: origin of replication
ter: terminus of replication
Segregation of DNA - DNA replication begins at the center of the cell, daughter DNA strand separates, ori regions move toward separate sides of the cell
Cytokinesis - cytoplasm is split and two daughter cells result
Chromosome number: number of chromosomes it has in total
Ploidy: number of homologous chromosomes that exists for each chromosome type
haploid (1n): only one chromosome for each chromosome type; human gametes
diploid (2n): two homologous chromosomes for each chromosome type; human somatic cells
Sister chromatids: two chromatids joined together at a common centromere
Centromere: region of chromosomes to which microtubules attach during cell division; has protein kinetochores = chromosome movement
Homologous chromosomes: in diploid organisms, chromosomes exist in homologous pairs
Nucleus: surrounded by membrane and contains DNA
Dna packaged by special proteins to form a complex called chromatin
Interphase: DNA is stretched out
Nucleolus: specialized structure in nucleus, synthesis of ribosomal RNA and assembly of rRNA into ribosomes
Centrosomes: regions near the nucleus that are associated with spindle fibers, organizing center for microtubules in the cell, site of synthesis and replication of microtubules
Centrioles: within centrosomes, pair of hollow microtubule rings in animals
Cytoskeleton: internal scaffolding, constructed of filaments, structure and mechanical support, dynamic
Signal to divide - growth factor initiates cell division (internal signal)
Replication of DNA - DNA replication occurs during the S-phase
Segregation of DNA - each daughter cells must have one copy of each chromosome, segregate into two new nuclei through mitosis
Cytokinesis - division of the cell into two daughter cells, plants: cell wall, animal: membrane
Interphase: mitosis is not occurring, cell synthesizes RNA, produces proteins, grows in size, nucleus and nucleolus visible, DNA replication occurs
Gap 1 (G1): cell grows, produces protein and RNA, prepares for protein synthesis, cells get stuck (G0)
Synthesis (S): DNA is duplicated through DNA replication upon the receipt of a proper signal
Gap 2 (G2): cell grows, produces proteins, microtubules, in prep for mitosis
Mitotic (M): parent cell divides into two daughter cells
mitosis: orderly division of the nucleus
cytokinesis: division of the cytoplasm
prophase: nucleolus fades, chromatin → chromosomes, microtubules disassemble, mitotic spindle forms
prometaphase: nuclear envelope is completely dissolved and some spindle fibers attach at the kinetochores
metaphase: chromosomes align at center
anaphase: chromatids pull apart, move to cell poles, spindle fibers shorten, cell elongates
telophase: spindle breaks down, nuclear envelopes and nucleoli re-form, chromosomes uncoil and become less compact
animals: formation of contractile ring of actin and myosin filaments along the metaphase plate
plants: occurs as vesicles from golgi move along microtubules, forming a cell plate membrane
G1 checkpoint: DNA synthesis will be delayed if DNA is damaged, will not continue again until the DNA has been repaired. this checkpoint reduces deleterious effects of DNA damage
S-phase checkpoint: DNA synthesis will be delayed if the DNA is damaged or if replication is incomplete
G2 checkpoint: the cell will not progress from the G2 phase to mitosis unless the DNA is undamaged and intact
M-phase checkpoint: cell will not go into anaphase unless chromosomes are properly aligned along the metaphase plate and kinetochores are attached to the spindle fibers. this checkpoint ensures the cell is ready for division before it proceeds any further
Regulation of the cell cycle is controlled by proteins called cyclins and cyclin-dependent kinases (CDKs)
kinase; phosphorylating enzyme
CDK binds to cyclin → allosteric change exposes active site on CDK → CDK phosphorylates proteins that regulate CDK cycle
every CDK has a specific cyclin that activates it, so cells can precisely control CDK activity by controlling the production and breakdown of cyclins
cyclins are produced in response to various signals, including presence of growth factors
sexual reproduction: combination of haploid gametes from two parents → diploid
Prophase I:
synaptonemal protein complex attaches homologs together, forming a tetrad/bivalent, with 2 homologous chromosomes and four homologous chromatids
synapsis: fusion of chromosome pairs
crossing over: DNA is exchanged between homologs at chiasmata = recombinant chromatids, increases genetic variation
spindle fibers form and attach to kinetochores
synaptonemal complex begins to break down and nuclear envelope breaks down
Metaphase I:
chromosomes line up along metaphase plate in homologous pairs
spindles from each pole attach to one chromosome of each pair
independent assortment
Anaphase I:
homologous chromosomes of each tetrad separate and move along the spindle fibers toward each pole as the kinetochore tubules shorten
Telophase I and Cytokinesis:
homologous chromosomes reach opposite poles
microtubules disappear
new nuclear membrane surrounds each haploid set
chromosomes uncoil
cytokinesis (pinching of cell membrane) completes creation of 2 daughter cells
sister chromatids separate, cells further divide into four haploid daughter cells with a single chromosome each
Prophase II:
chromosomes condense, spindle forms, chromosomes move toward metaphase plate
Metaphase II:
chromosomes meet at the metaphase plate, spindle fibers of each pole attach to the kinetochores of the sister chromatids
Anaphase II:
centromeres of the sister chromatids separate
sister chromatids move toward opposite poles
sister chromatids are now called chromosomes
Telophase II and Cytokinesis:
splitting of the cell into two daughter cells, chromosomes uncoil
total of four haploid gametes are formed
Mitosis: process of nuclear division in eukaryotic cells that conserves the chromosome number by equally allocating replicated chromosomes to each of the daughter nuclei
Meiosis: two-stage type of cell division in sexually reproducing organisms that results in four cells with half the chromosome number of the original number of the original cell
Event | Mitosis | Meiosis |
---|---|---|
DNA Replication | Interphase (S) | Interphase (S) |
# of Cell Divisions | 1 | 2 |
Number of Daughter Cells | 2 | 4 |
Ploidy of Daughters | 2n (diploid) | 1n (haploid) |
Synapsis of Homologs | no | yes (early prophase I) |
Crossing over/Recombination | no | yes (late prophase I) |
Biological purpose | duplicating cells | generating gametes |
Males: spermatogenesis, generate gametes throughout their lives, prophase I lasts 1 week
Females: born with all oogonia, prophase I begins before birth, meiotic process stops until puberty
Recombination: genetic variation
Independent Assortment: during meiosis I, the chromosomes line up in a random fashion along the metaphase plate
Crossing Over: prophase I of meiosis 1, crossing over of chromosomes occurs
Nondisjunction: occurs when homologous pairs fail to separate in anaphase I, or sister chromatids fail to separate in anaphase II
Aneuploidy: chromosomal abnormality in which a person has an abnormal number of chromosomes in his or her genome
Monosomy: one chromosome lacks a homologous partner
almost always lethal
turner syndrome: nonlethal, only one X chromosome
Trisomy: three copies of one chromosome type
trisomy 16: most common, miscarriage
trisomy 21 (down syndrome): 3 copies of 21st chromosome
Polyploidy: abnormal amount of chromosome sets
can result from an extra round of DNA replication before meiosis or lack of spindle formation in meiosis in II
most common: triploidy (3n) or tetraploidy (4n)
Translocation: occurs when there is a crossover between nonhomologous chromosomes
Apoptosis: programmed cell death
detach from neighbors, break chromatin apart into small pieces, form blebs: membranous lobes that break into fragments
remains are ingested by surrounding cells in phagocytosis
external signals: lack of mitotic signal
internal signals: recognition of damaged DNA
Cancer: disease caused by uncontrolled cell division of abnormal cells in the body
oncogene proteins (positive regulators): positively regulate the cell cycle in cancer cells, cause cells to progress through cell cycle more quickly → higher than normal cell division
tumor suppressors (negative regulators): negatively regulate the cell cycle in normal cells, slow the process of cell division down → inactive in cancer cells