Unit 1.6 - Cell division Flashcards
Chromosome
Long, thin structure of DNA and protein in nucleus of eukaryotic cells carrying the genes.
Chromatid
One of the two identical copies of a chromosome, joined at centromere prior to cell division.
Centromere
Specialised region of chromosome where 2 chromatics join, microtubules of spindle attach at cell division.
1) What are chromosomes made of?
2) When do they become visible?
1) DNA and histone.
2) Chromatin condenses prior to cell division.
1) 2 copies of a chromosome are called ……
2) They lie parallel to their length and are joined at the…..
1) sister chromatids.
2) centromere.
Haploid (human gametes) - n
One complete set of chromosomes.
Homologous pairs
Chromosomes pairs identical in size and shape, carry same gene loci, with genes for same characteristics. One chromosome of each pair comes from each parent.
Diploid (human body cells) - 2n
Two complete sets of chromosomes.
1) How many chromosomes does a human have?
2) How may homologous chromosomes?
1) 46
2) 23
Ploidy level
Number of complete sets of chromosomes in an organism.
Polyploid
Organisms with more than two complete sets of chromosomes.
Mitosis
Type of cell division: 2 daughter cells have same number of chromosomes and are genetically identical with each other and the parent cell.
Cell cycle
Sequence of events that takes place between one cell division and the next.
State the stages of mitosis (6).
Interphase, prophase, metaphase, anaphase, telophase, cytokinesis.
What occurs during interphase? (longest phase of cell cycle)
Organelle replication, DNA replication, cell growth, protein synthesis (uses ATP).
1) Why are chromosomes not visible during interphase?
2) Why is it not a resting phase?
1) Chromatin is dispersed throughout the nucleus.
2) Cells biochemically active.
Prophase
1) What happens to the chromosomes?
2) What happens to the chromatids?
3) What happens to the nuclear envelope and nucleolus?
1) Chromosomes condense (pair of chromatids).
2) Can be seen lying free in cytoplasm.
3) Nuclear envelope disintegrates and nucleolus disappears.
Prophase (longest stage of mitosis)
1) What happens to the centrioles present in animal cells?
2) How is the spindle formed?
3) What happens to the spindle?
1) Pairs separate, move to opposite poles and join again.
2) Protein microtubules form, radiating from each centriole, making spindle.
3) Fibres extend from pole to pole & pole to centromere of each chromosome.
Are chromosomes or chromatids genetically identical?
Chromatids.
Metaphase
1) What happens to the chromosomes?
2) What happens at the centromere?
1) Each chromosome pair of chromatids joined at centromere.
2) Centromere attaches to spindle fibres so chromosomes are aligned on equator.
Anaphase
1) What happens to the spindle fibres?
2) What happens to the centromeres?
3) What happens to the chromatids?
1) Shorten.
2) Separate.
3) Pulls separated chromatids to the poles, centromere first.
Telophase
1) What happens to the chromosomes?
2) What happens to the spindle fibres?
3) What happens to the nuclear envelope and nucleolus?
1) Uncoil and lengthen.
2) Break down.
3) Nuclear envelope reforms, nucleolus reappears.
1) What is cytokinesis?
2) How does it occur in animal cells?
1) Division of cytoplasm to form 2 daughter cells.
2) Constriction of parent cell around equator, from the outside, inwards.
How does cytokinesis occur in plant cells?
Droplets of cell wall (cell plate) form across equator of parent cell from the centre outwards. Extend and join to form new cell wall.
Mitosis
State the difference of the following in animal and plant cells:
1) Shape
2) Centrioles
1) A = Cell becomes rounded before mitosis, p = no change.
2) A = present, p = absent from higher plant cells.
Mitosis
State the difference of the following in animal and plant cells:
1) Cytokinesis
1) A = Cleavage furrow develops from the outside inwards, p = cell plate develops from the centre inwards.
Mitosis
State the difference of the following in animal and plant cells:
1) Spindle
2) Occurence
1) A = degenerates at telophase, p = remains throughout new cell wall formation.
2) A = epithelia and bone marrow, hair follicles, tissue repair , p = in meristems.
What is the importance of mitosis? (4)
Genetic stability, growth, repair of tissues and asexual reproduction.
1) What is asexual reproduction?
2) What organisms does it take place in?
1) Offspring that are genetically identical to the parent so no genetic variation.
2) Unicellular - bacteria, insects, flowering plants such as bulbs.
Proto-oncogene
Gene which, when mutated, becomes an oncogene and contributes to development of cancer.
Oncogene
Gene which causes uncontrolled cell division (cancer).
What are tumour suppressor genes?
Prevent rapid replication of cell cycle.
What happens genes are mutated in:
1) Solid tissue
2) Bone marrow
1) Tumour forms in wall of colon.
2) Immature blood cells accumulate that they spill out into general circulation as blood cancers e.g. leukaemia.
Meiosis
2 stage cell division in sexually reproducing organisms that produces 4 genetically distinct haploid gametes (daughter cells) each with half the number of chromosomes of the parent cell.
1) What happens to the zygote when 2 haploid gametes fuse at fertilisation?
2) What would happen to the number of chromosomes if it didn’t halve during gamete formation?
1) Zygote has 2 sets of chromosomes restoring the diploid condition.
2) Number of chromosomes would double every generation.
What is the main difference between meiosis 1 and 2 during anaphase? (no more DNA replication)
1 = homologous chromosomes separate 2 = chromatids separate
Bivalent
Association of 2 chromosomes of a homologous pair at prophase 1 of meiosis.
Chiasmata
Seen through light microscope where chromosomes exchange DNA in genetic crossing over.
Crossing over
Reciprocal exchange of genetic material between chromatids of homologous chromosomes during synapsis in prophase I of meiosis.
What is the pairing of chromosomes called in meiosis I?
Synapsis, each pair is bivalent.
State what happens to the following during prophase I:
1) Chromosomes
2) Centrioles
3) Nuclear envelope and nucleolus
1) Coil up, condense (short and thick), seen as 2 chromatids.
2) Separate move to poles. Organises polymerisation of microtubules and form spindle.
3) Disintegrated, nucleolus disappeared.
What causes genetic variation in meiosis I?
At chiasma exchange DNA called crossing over. It mixes genes from 2 parents in one chromosome.
1) What happens to the pair of homologous chromosomes during metaphase I?
2) What does independent assortment allow?
1) Arrange themselves randomly on equator of spindle.
2) New genetic combinations, genes from both parents going into both new daughter cells.
Anaphase I
1) Chromosomes
2) Spindle fibres
3) Poles
1) In each bivalent separate.
2) Shorten, each pair pulled to one pole.
3) Receives 1 homologous pair of chromosomes and random mixture of maternal and paternal.
Telophase I - cytokinesis to meiosis II
1) Nuclear envelope and chromosomes in some species.
2) Chromosomes in may species.
1) Reforms around haploid group of chromosomes, decondense so aren’t visible.
2) Stay in condensed form.
What happens to the centrioles during prophase II?
Separate and organise new spindle at right angles to old spindle.
Metaphase II (different combination chromatids)
1) Chromosomes
2) What process occurs?
1) Line up on equator, attached to a spindle fibre by its centromere.
2) Independent assortment because chromatids of the chromosomes can face either pole.
Anaphase II
1) Spindle fibres
2) Centromeres
1) Shorten.
2) Separate, pulling chromatids to opposite poles.
Telophase II - cytokinesis to 4 haploid daughter cells
1) Chromatids
2) Spindle
3) Nuclear envelope & nucleoli
1) Lengthen and can’t be distinguished in the microscope.
2) Disintegrates.
3) Re-forms.
Explain the significance of meiosis (2).
Chromosome number constant from one generation to the next, genetic variation in gametes and zygotes that they produce.
How does meiosis achieve genetic variation?
Independent assortment at metaphase I & II, crossing over/exchanging DNA during prophase I.
State differences between meiosis I & II during prophase.
1 = follows DNA replication & crossing over 2 = doesn't
State differences between meiosis I & II during metaphase.
1 = homologous pairs either side of equator, independent assortment chromosomes. 2 = chromosomes on equator, independent assortment at chromatids.
State differences between meiosis I & II during anaphase.
1 = separation at chromosomes, 2 daughter cells, haploid. 2 = separation at chromatids, 4 daughter cells, haploid.
State the differences between mitosis and meiosis:
1) Divisions
2) Daughter cells
3) Chromosome number in cells
4) Ploidy of daughter cells
1) 1, 2
2) 2, 4
3) Same as parent, half of parent
4) Diploid, Haploid
State the differences between mitosis and meiosis:
1) Chiasmata
2) Genetic crossing over
3) Independent assortment
4) Genetic composition
1) Absent, present
2) None, prophase I
3) None, metaphase I & II
4) Genetically identical with parent and each other, genetically different.
