DNA and Inheritance Flashcards
What happens during nuclear division in somatic cells (mitosis and meiosis) and cytoplasmic division (cytokinesis)?
Eukaryotic cells pass on their instructions for growth and development from 1 generation of cell to the next.
How many daughter cells do mitosis and cytokinesis result in?
2 daughters cells (identical sets of chromosomes)
Define cell cycle?
The sequence of events from one cell division to another.
The length of the cell cycle varies in different cells
What are the 5 phases of mitosis?
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
What are the 3 phases in interphase?
G₁ phase
S phase
G₂ phase
What occurs during G₁ phase?
Cell metabolically active
Duplicates organelles and cytosolic components
Starts replicating centrosomes
What occurs during S phase?
DNA is replicated
What occurs during G₂ phase?
Cell growth continues
Enzymes and other proteins are synthesised
Replication of centrosomes is complete
What occurs during prophase?
Chromosomes condense and become visible
Spindle fibres emerge from the centrosomes
Nuclear envelope breaks down
Nucleolus disappears
What occurs during metaphase?
Mitotic spindle is fully developed
Centrosomes are at opposite poles of the cell
Chromosomes are lined up at the metaphase plate
Each sister chromatid is attached to a spindle fibre
What occurs during anaphase?
Cohesin proteins binding sister chromatids together break down
Sister chromatids (now called chromosomes) are pulled towards opposite poles
What occurs during telophase?
Chromosomes arrive at opposite poles and begin to de-condense
Nuclear envelope material surrounds each set of chromosomes
The mitotic spindle breaks down
What occurs during Cytokinesis?
Animal cells-a cleavage furrow separates daughter cells
Plant cells-a cell plate separates daughter cells
Define metacentric.
Centromere in the centre
Define submetacentric.
Centromere nearer to one end than the other
Define acrocentric.
Centromere close to one end
Define telocentric.
Centromere on the end
Define apoptosis.
Aprogrammed series of events that lead to cell death as a result of dismantling of the internal contents of the cell (DNA shredded) by various enzymes including caspases
Define phagocytes.
Scavenging cells that clear apoptotic bodies.
Particularly macrophages.
What problems arise if apoptosis fails?
Cancer
Developmental defects
What occurs during apoptosis?
Programmed death is signalled
Cell volume decreases
Membrane bulges outward
Nucleus fragments as cell destroys it
Apoptotic bodies form
Apoptotic debris is engulfed by macrophage
How does cytokinesis occur in plant cells?
Cytoplasm of plant cells divides with the formation of a cell plate
Cellulose is deposited at cell plate forming a wall that divides the parent cell into 2 daughter cells – each with a plasma membrane
How does cytokinesis occur in animal cells.
Cytoplasm divides by cleavage
Plasma membrane around the middle of cell draws together to form a cleavage furrow
Cleavage furrow continues until edges meet and cell is cleaved (results in 2 daughter cells)
May result in unequal distribution of proteins (asymetrical cell division)
Describe binary fission.
Produces 2 daughter cells
Produces the same number of chromosomes as parental cell
Why do prokaryotes undergo binary fission?
Lack nucleus
Single chromosome with no centromere
Not considered proper mitosis
What occurs during binary fission?
DNA replicates (2 chromosomes)
Each copy attaches to a different part of the cell membrane
When cell pulls apart, original and replicate chromosomes are separated
A wall forms across the cell and divides into 2 cells of identical genetic composition
Where does meiosis occur?
Specialised organs of sexually reproducing animals and plants
What does meiosis produce?
Gametes (sex cells) – sperm and egg/ ova
4 daughter cells
What occurs during prophase I?
Chromosomes condense, nucleolus disappears & spindle forms with centrioles at opposite ends
Homologous chromosomes lie side by side (synapsis)
A pair of chromosomes (1 maternal & 1 paternal) now called a bivalent
What occurs during metaphase I?
Nuclear envelope breaks down
Homologous chromosomes move together to equator of spindle
What occurs during anaphase I?
Maternal & paternal chromosomes of homologous pairs move to opposite poles of spindle.
The separation or disjunction of each pair of homologous chromosomes occurs independently
What occurs during telophase I?
Spindle breaks down, cell starts to separate across its middle & nuclear envelopes form around the 2 new nuclei
What occurs at the end of meiosis I?
A brief interphase
DNA does not duplicate during this interphase
What occurs during prophase II?
New spindle forms at right angles to the first one
What occurs during metaphase II?
Chromosomes move to equator of spindle
What occurs during anaphase II?
Chromatids separate and move apart from each other
Chromatids become the chromosomes of the daughter cells
When they reach the poles, the cells enter telophase
What occurs during telophase II?
Spindle apparatus disappears
Chromosomes de-condense to their thread-like form
New nuclear envelopes and nucleoli form
Compare function of mitosis and meiosis.
Mitosis
- Nuclear & cell division for growth, repair & replacement of tissues
Meiosis
- Nuclear & cell division for producing sex cells (gametes)
Compare the locations in which mitosis and meiosis occur.
Mitosis
- Takes place in somatic cells
Meiosis
- Takes place in gonads or reproductive organs (e.g. ovaries & testes of mammals; ovaries & anthers of flowering plants)
Compare outputs of mitosis and meiosis.
Mitosis
- Two cells are the outputs
Meiosis
- Four cells (gametes) are the outputs
Compare number of cell divisions in mitosis and meiosis.
Mitosis
- One cell division completes the process
Meiosis
- Two cell divisions complete the process
Compare the number of chromosomes in each daughter cell in mitosis and meiosis.
Mitosis
- Each daughter contains the diploid (2n) of chromosomes
Meiosis
- Each daughter contains the haploid (n) of chromosomes
Compare the way in wich organisms reproduce using mitosis or meiosis.
Mitosis
- Asexually reproducing organisms reproduce by mitotic division of cells
- Prokaryotes reproduce by binary fission not mitosis
Meiosis
- Sexually reproducing organisms reproduce by fusion of gametes, restoring the diploid number (2n) of chromosomes of each cell
Compare the amount of variation produced my mitosis and meiosis.
Mitosis
- New cells of this kind show no variation unless mutations or environmental influences (genetically identical – clones)
- Variation & diversity of offspring are narrowed
Meiosis
- Offspring produced show variation between them
- Variation and diversity of offspring are increased
Compare the applications of mitosis and meiosis.
Mitosis
- Tissue culture (skin grafts & cloning plants)
Meiosis
- Creating new varieties of organisms
