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AS Biology Unit 1 + 2 > Unit 1.6 - Cell division > Flashcards

Unit 1.6 - Cell division Flashcards

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1
Q

Chromosome

A

Long, thin structure of DNA and protein in nucleus of eukaryotic cells carrying the genes.

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2
Q

Chromatid

A

One of the two identical copies of a chromosome, joined at centromere prior to cell division.

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3
Q

Centromere

A

Specialised region of chromosome where 2 chromatics join, microtubules of spindle attach at cell division.

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4
Q

1) What are chromosomes made of?

2) When do they become visible?

A

1) DNA and histone.

2) Chromatin condenses prior to cell division.

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5
Q

1) 2 copies of a chromosome are called ……

2) They lie parallel to their length and are joined at the…..

A

1) sister chromatids.

2) centromere.

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6
Q

Haploid (human gametes) - n

A

One complete set of chromosomes.

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7
Q

Homologous pairs

A

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.

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8
Q

Diploid (human body cells) - 2n

A

Two complete sets of chromosomes.

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9
Q

1) How many chromosomes does a human have?

2) How may homologous chromosomes?

A

1) 46

2) 23

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10
Q

Ploidy level

A

Number of complete sets of chromosomes in an organism.

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11
Q

Polyploid

A

Organisms with more than two complete sets of chromosomes.

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12
Q

Mitosis

A

Type of cell division: 2 daughter cells have same number of chromosomes and are genetically identical with each other and the parent cell.

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13
Q

Cell cycle

A

Sequence of events that takes place between one cell division and the next.

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14
Q

State the stages of mitosis (6).

A

Interphase, prophase, metaphase, anaphase, telophase, cytokinesis.

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15
Q

What occurs during interphase? (longest phase of cell cycle)

A

Organelle replication, DNA replication, cell growth, protein synthesis (uses ATP).

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16
Q

1) Why are chromosomes not visible during interphase?

2) Why is it not a resting phase?

A

1) Chromatin is dispersed throughout the nucleus.

2) Cells biochemically active.

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17
Q

Prophase

1) What happens to the chromosomes?
2) What happens to the chromatids?
3) What happens to the nuclear envelope and nucleolus?

A

1) Chromosomes condense (pair of chromatids).
2) Can be seen lying free in cytoplasm.
3) Nuclear envelope disintegrates and nucleolus disappears.

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18
Q

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?

A

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.

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19
Q

Are chromosomes or chromatids genetically identical?

A

Chromatids.

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20
Q

Metaphase

1) What happens to the chromosomes?
2) What happens at the centromere?

A

1) Each chromosome pair of chromatids joined at centromere.

2) Centromere attaches to spindle fibres so chromosomes are aligned on equator.

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21
Q

Anaphase

1) What happens to the spindle fibres?
2) What happens to the centromeres?
3) What happens to the chromatids?

A

1) Shorten.
2) Separate.
3) Pulls separated chromatids to the poles, centromere first.

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22
Q

Telophase

1) What happens to the chromosomes?
2) What happens to the spindle fibres?
3) What happens to the nuclear envelope and nucleolus?

A

1) Uncoil and lengthen.
2) Break down.
3) Nuclear envelope reforms, nucleolus reappears.

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23
Q

1) What is cytokinesis?

2) How does it occur in animal cells?

A

1) Division of cytoplasm to form 2 daughter cells.

2) Constriction of parent cell around equator, from the outside, inwards.

24
Q

How does cytokinesis occur in plant cells?

A

Droplets of cell wall (cell plate) form across equator of parent cell from the centre outwards. Extend and join to form new cell wall.

25
Q

Mitosis
State the difference of the following in animal and plant cells:
1) Shape
2) Centrioles

A

1) A = Cell becomes rounded before mitosis, p = no change.

2) A = present, p = absent from higher plant cells.

26
Q

Mitosis
State the difference of the following in animal and plant cells:
1) Cytokinesis

A

1) A = Cleavage furrow develops from the outside inwards, p = cell plate develops from the centre inwards.

27
Q

Mitosis
State the difference of the following in animal and plant cells:
1) Spindle
2) Occurence

A

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.

28
Q

What is the importance of mitosis? (4)

A

Genetic stability, growth, repair of tissues and asexual reproduction.

29
Q

1) What is asexual reproduction?

2) What organisms does it take place in?

A

1) Offspring that are genetically identical to the parent so no genetic variation.
2) Unicellular - bacteria, insects, flowering plants such as bulbs.

30
Q

Proto-oncogene

A

Gene which, when mutated, becomes an oncogene and contributes to development of cancer.

31
Q

Oncogene

A

Gene which causes uncontrolled cell division (cancer).

32
Q

What are tumour suppressor genes?

A

Prevent rapid replication of cell cycle.

33
Q

What happens genes are mutated in:

1) Solid tissue
2) Bone marrow

A

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.

34
Q

Meiosis

A

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.

35
Q

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?

A

1) Zygote has 2 sets of chromosomes restoring the diploid condition.
2) Number of chromosomes would double every generation.

36
Q

What is the main difference between meiosis 1 and 2 during anaphase? (no more DNA replication)

A 
1 = homologous chromosomes separate
2 = chromatids separate
37
Q

Bivalent

A

Association of 2 chromosomes of a homologous pair at prophase 1 of meiosis.

38
Q

Chiasmata

A

Seen through light microscope where chromosomes exchange DNA in genetic crossing over.

39
Q

Crossing over

A

Reciprocal exchange of genetic material between chromatids of homologous chromosomes during synapsis in prophase I of meiosis.

40
Q

What is the pairing of chromosomes called in meiosis I?

A

Synapsis, each pair is bivalent.

41
Q

State what happens to the following during prophase I:

1) Chromosomes
2) Centrioles
3) Nuclear envelope and nucleolus

A

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.

42
Q

What causes genetic variation in meiosis I?

A

At chiasma exchange DNA called crossing over. It mixes genes from 2 parents in one chromosome.

43
Q

1) What happens to the pair of homologous chromosomes during metaphase I?
2) What does independent assortment allow?

A

1) Arrange themselves randomly on equator of spindle.

2) New genetic combinations, genes from both parents going into both new daughter cells.

44
Q

Anaphase I

1) Chromosomes
2) Spindle fibres
3) Poles

A

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.

45
Q

Telophase I - cytokinesis to meiosis II

1) Nuclear envelope and chromosomes in some species.
2) Chromosomes in may species.

A

1) Reforms around haploid group of chromosomes, decondense so aren’t visible.
2) Stay in condensed form.

46
Q

What happens to the centrioles during prophase II?

A

Separate and organise new spindle at right angles to old spindle.

47
Q

Metaphase II (different combination chromatids)

1) Chromosomes
2) What process occurs?

A

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.

48
Q

Anaphase II

1) Spindle fibres
2) Centromeres

A

1) Shorten.

2) Separate, pulling chromatids to opposite poles.

49
Q

Telophase II - cytokinesis to 4 haploid daughter cells

1) Chromatids
2) Spindle
3) Nuclear envelope & nucleoli

A

1) Lengthen and can’t be distinguished in the microscope.
2) Disintegrates.
3) Re-forms.

50
Q

Explain the significance of meiosis (2).

A

Chromosome number constant from one generation to the next, genetic variation in gametes and zygotes that they produce.

51
Q

How does meiosis achieve genetic variation?

A

Independent assortment at metaphase I & II, crossing over/exchanging DNA during prophase I.

52
Q

State differences between meiosis I & II during prophase.

A 
1 = follows DNA replication & crossing over
2 = doesn't
53
Q

State differences between meiosis I & II during metaphase.

A 
1 = homologous pairs either side of equator, independent assortment chromosomes.
2 = chromosomes on equator, independent assortment at chromatids.
54
Q

State differences between meiosis I & II during anaphase.

A 
1 = separation at chromosomes, 2 daughter cells, haploid.
2 = separation at chromatids, 4 daughter cells, haploid.
55
Q

State the differences between mitosis and meiosis:

1) Divisions
2) Daughter cells
3) Chromosome number in cells
4) Ploidy of daughter cells

A

1) 1, 2
2) 2, 4
3) Same as parent, half of parent
4) Diploid, Haploid

56
Q

State the differences between mitosis and meiosis:

1) Chiasmata
2) Genetic crossing over
3) Independent assortment
4) Genetic composition

A

1) Absent, present
2) None, prophase I
3) None, metaphase I & II
4) Genetically identical with parent and each other, genetically different.

AS Biology Unit 1 + 2 (4 decks)

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