Cell Division Flashcards
How does life continue ?
- All cells originate from pre-existing cells.
- For life to continue, genetic information must be transferred to the next generation.
What is the process of asexual reproduction?
- New individuals are formed from just one parent.
- The offspring are genetically identical to the parent and each other.
- Involves mitosis.
What is mitosis?
A type of nuclear division in somatic cells that maintains the parental diploid number of chromosomes in the daughter cells; it is the basis of bodily growth and asexual reproduction in many eukaryotic species
what is the first stage of mitosis ?
Interphase
What happens during interphase ?
- Centrosomes and DNA are replicated.
- DNA begins to condense.
- In a human cell this stage takes approx 22 hours.
what is the second stage of mitosis ?
Early prophase
What happens during early prophase ?
- Chromosomes continue to condense, making them easily visible under the light microscope.
- The nuclear membrane slowly starts to disintegrate.
- The cell completes the prophase stage in 19 minutes approx.
What is the third stage of mitosis?
Late prophase
What happens during late prophase?
- Chromatids visible as chromosomes shorten and thicken.
- Nucleolus disappears.
- Nuclear envelope disappears.
What is the fourth stage of mitosis?
Metaphase
What happens during metaphase?
- The spindles are fully developed and are made up of a mixture of microtubules and proteins.
- The paired chromosomes (chromatids) are aligned across the equator of the cell.
- The spindles extend from the poles at either end of the cell and attach themselves to the chromatids aligning them exactly in the centre of the cell separating the two poles.
- Over time each chromosome splits longitudinally into two identical chromatids.
What is the fifth stage of mitosis?
Anaphase
What happens during anaphase?
The chromatids abruptly separate and move towards the spindle poles. This is achieved by shortening of the microtubules, and forces are mainly exerted at the microtubules.
What is the final stage of mitosis?
Telophase
What happens during telophase?
- Two new nucleoli and nuclear envelopes form using fragments of the parent cell’s nuclear membrane, and the chromatin fibres from each chromosome uncoil inside them.
- Finally, the mitotic spindles disappear and mitosis is finished, chromosomes regain their threadlike form.
What is the final product of mitosis?
Cytokinesis
What happens during cytokinesis ?
- The cytoplasm divides between the two daughter cells in order to form two relatively complete cells.
- This stage also includes the division of the cell membrane, creating two structurally independent cells.
What happens during cytokinesis in plants ?
- involves the formation of a cell plate, cellulose is deposited on the cell plate to complete the cell walls of the two new daughter cells.
What happens during cytokinesis in animals?
a cleavage furrow is created.
What is asexual reproduction in prokaryotes ?
Binary Fission
What happens during binary fission ?
- involves division of the parent body into two, fairly equal parts to produce two identical cells.
- Has no spindle
- Fast
What is Binary fission ?
- The division of a cell into two cells without mitosis, a prokaryotic cell undergoes binary fission to form two identical daughter cells, a form of asexual reproduction
What are gametes ?
New individuals are formed by the joining of two sex cells
The joining of two gametes is called ?
Fertilisation
During fertilisation what is formed?
Zygote
How do you increase variation in a genotype?
The offspring are genetically different from their parents and each other
How are gametes formed ?
meiosis
What is meiosis ?
the process in eukaryotic, sexually-reproducing organisms that reduces the number of chromosomes in a cell before reproduction.
what is the process of meiosis ?
A type of cellular division in sexually reproducing organisms that involves two rounds of cell division, but only one round of DNA replication; during meiosis the chromosome number of a cell is halved so that the daughter cells are haploid; meiosis is the basis of gamete formation
What happens during interphase in meiosis ?
- Chromosomes (DNA) replicates
- Each duplicated chromosome consists of two identical sister chromatids attached at their centromeres
- Centriole pairs also replicate
- Nucleus and nucleolus visible
What are tetrads ?
Homologous pairs that carry genes controlling the same inherited traits
What happens during prophase 1
- The longest and most complex phase
- Chromosomes condense
- Synapsis occurs: homologous chromosomes come together to form a tetrad
- Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids)
What is a homologous chromosomes ?
Pair of chromosomes (maternal and paternal) that are similar in shape and size
What is a locus?
position of the gene
What is the process of crossing over ?
- Crossing over may occur between non-sister chromatids at the chiasmata
- Crossing over: segments of non-sister chromatids break and reattach to the other chromatid
- Chiasmata (chiasma) are the sites of crossing over
What happens during metaphase 1?
- Tetrads align on the metaphase plate.
- INDEPENDENT ASSORTMENT OCCURS:
The orientation of homologous pairs to poles is random. -> Variation
what happens during anaphase 1?
- Homologous chromosomes separate and move towards the poles.
- Sister chromatids remain attached at their centromeres.
what happens during Telophase 1?
- Each pole now has a haploid set of chromosomes.
-Cytokinesis occurs and two haploid daughter cells are formed.
What happens during prophase II ?
-Spindles start to form, usually at right angles to one formed in meiosis I
What happens during metaphase II?
-Chromosomes arrange themselves on the equator
What happens during Anaphase II?
- Chromatids pull apart and move to opposite poles
What happens during telophase II ?
- Nuclei form
- Cytokinesis occurs
What is the significance of meiosis?
- Halving the chromosome number ensures that when gametes with the haploid number fuse to form a zygote the normal diploid number is restored.
What is fertilisation?
The fusion of haploid male and female gametes during sexual reproduction to produce a diploid zygote; the random union of gametes is known as random fertilisation
What are the two types of fertilaistion?
- internal fertilisation
- external fertilisation
What is internal fertilsation?
- When the sperm and ovum unite inside the female’s body.
What is external fertilisation?
- When the sperm and ovum unite outside the female’s body.
