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bio > chapter 16 cell division > Flashcards

chapter 16 cell division Flashcards

1
Q

what is mitosis

A

form of nuclear division that produces daughter nuclei containing the same number of chromosomes as the parent cells = daughter cells are genetically identical to parent cells

– only occurs in cells with nuclei, but can be any cell

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2
Q

what occurs in interphase

A

→ cells carry out activities to prepare for mitosis - absorbing nutrients, building up protoplasm
→ chromosomes appear as chromatin (long thin threads)
→ centrioles divide in animal cells
→ DNA replication occurs: each chromatin thread replicates to form 2 identical chromatin threads - joined at centromere = sister chromatids → to ensure the chromosome number in parent cell is same as in the daughter cells
Eg 4 chromatin in parent cell = 4 pairs of sister chromatids (number of centromere = number of chromosomes)

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3
Q

what occurs in prophase

A

in picture: clump of cells
chromatin threads condense, coil and shorten (CCR) = become chromosome (1 pair of chromatin thread = 1 chromosome)
→ by end of prophase:
- nucleolus and nuclear envelope disappear
- 2 pairs of centrioles move to opposite ends of the cell
- asters form around centrioles
- Spindle forms with spindle fibres extending from 1 pole of the cell to the other

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4
Q

what occurs in metaphase

A

chromosomes line up along equatorial plane of spindle - centromere of each chromosome is attached on both sides to a spindle fibre

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5
Q

what occurs in anaphase

A

→ centromere divides (chromosomes are no longer connected = form chromatids) - spindle fibres shorten -> pull chromatids apart to opposite poles of cell
→ separated chromatids = form daughter chromosomes (eg 4 chromosomes = 8 chromatids with one centromere each = 8 daughter chromosomes)

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6
Q

what occurs in telophase

A
  1. Spindle fibres break down
  2. Nuclear envelope forms around daughter chromosomes at each pole = forms 1 nucleus at each pole (each nucleus has equal number of chromosomes)
  3. Nucleolus reforms in each nucleus
  4. Daughter chromosomes uncoil and lengthen = form thin chromatin threads (1 daughter chromosome = 1 chromatin thread)
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7
Q

what happens in cytokinesis

A

→ cleavage/furrows appear in cytoplasm between the 2 nuclei
→ furrows deepen = the 2 nuclei separate - produce 2 identical daughter cells

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8
Q

why is mitosis important

A

Mitosis enables growth of organism
→ mitosis produces new genetically identical cells for the organism to grow
Mitosis is needed for repair of worn out parts of the body
→ produces new cells that replace damaged cells
Mitosis allows asexual reproduction in plants to occur
→ grow daughter cells that are genetically identical to the parent cell

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9
Q

why must genetically identical daughter cells be produced

A

→ ensure that all daughter cells are genetically stable (genetically identical to parent cell) = all DNA is replicated for subsequent cell division/differentiation = future daughter cells are genetically identical
→ if error in DNA replication - new DNA strand formed (replicated) would be different from original = gene mutation in new daughter cell
→ gene mutation can cause abnormal proteins to be formed/uncontrolled division of cells - lead to excess cells that can form tumour (lead to cancer)

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10
Q

what is meiosis

A

→ a form of nuclear division that produces daughter nuclei containing half the number of chromosomes (haploid = n) as the parent nucleus (diploid = 2n)
→ occurs in gametes only (reproductive cells)

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11
Q

what happens in interphase (meiosis)

A

→ DNA replication: chromatin threads replicate - form 2 identical sister chromatids - 1 pair of sister chromatids attached at centromere (eg 4 chromatin threads = 8 sister chromatids = 4 pairs of sister chromatins = 8 chromosomes)
– each nucleus has (at least) 1 maternal chromatin and 1 paternal chromatin = after replication, forms 1 pair of maternal sister chromatids and 1 pair of paternal sister chromatids
→ pair of centrioles divide

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12
Q

what happens in prophase l

A
  1. each pair of sister chromatids go through CCR = become chromosomes (eg 1 pair of maternal sister chromatids = 1 pair of maternal chromosome)
  2. synapsis occurs: formation of homologous chromosome by pairing up - 1 paternal and 1 maternal chromosome pair up along whole length
  3. crossing over: non sister chromatids from each (maternal and paternal) homologous chromosome may break and exchange parts with each other = produces new combinations of genes along the chromosomes
  4. Homologous chromosomes repel each other
  5. Asters form around centrioles - centrioles move to opposite ends of cell
  6. Spindle fibres form
  7. Nuclear envelope and nucleolus disappear
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13
Q

what happens in metaphase l

A

→ pairs of homologous chromosomes arrange themselves along equatorial plane - two chromosomes of each pair face opposite poles of the cell
→ centromere of each chromosome is attached to a spindle fibre

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14
Q

what happens in anaphase l

A
  1. spindle fibres shorten = homologous chromosomes separate, pulled to opposite poles of cell
  2. chromosomes in the homologous chromosome do not separate into chromatids = one chromosome separates from the other chromosome (centromeres separate but do not divide - 1 homologous chromosome is made up of 2 chromosomes)
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15
Q

what happens in telophase l

A

→ nuclear envelope forms around chromosomes at each pole of the cell

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16
Q

what happens in cytokinesis l

A

→ furrows form in cytoplasm between the 2 cells - furrows deepen = produces 2 daughter cells with haploid number of chromosomes
→ centrioles divide
Meiosis does not stop here - do not take number of chromosomes in daughter cells here as final number

17
Q

what happens in prophase ll

A

→ two pairs of centrioles move to opposite poles of cell
→ nuclear envelope disappears, spindle fibres appear

18
Q

what happens in metaphase ll

A

→ chromosomes arrange themselves along equatorial plane (chromosomes are in form of 1 chromosome = 1 pair of sister chromatids)

19
Q

what happens in anaphase ll

A

→ centromere divides, spindle fibres shorten
→ sister chromatids of each chromosome separate = form daughter chromosomes - pulled to opposite poles of the cell

20
Q

what happens in telophase ll

A

spindle fibres disappear
Nuclear envelope forms around daughter chromosomes at each side of the cell
Nucleolus reforms

21
Q

what happens in cytokinesis ll

A

→ furrows form in cytoplasm between the 2 daughter cells in each daughter cell - furrows deepen and separate the cells = form 4 daughter cells
–> chromosomes unravel into chromatin = each daughter cell has half the number of chromosomes (chromatin) as parent cell

22
Q

why is meiosis important

A
  1. produces haploid gametes: nucleus of male gamete fuses with nucleus of female gamete during fertilisation = the diploid number of chromosomes is restored in zygote = maintaining correct number of chromosomes in the species
  2. Results in genetic variations → crossing over of non-sister chromatids in homologous chromosomes and independent assortment of chromosomes = increases chances of survival of species during changes in environment = those that survive will pass on favourable traits to offspring
23
Q

how can meiosis cause genetic variation

A
  1. Crossing over in prophase l only
    → non-sister chromatids (chromatids from different chromosomes) of homologous chromosomes may cross-over in prophase I of meiosis = crossing-over results in new combinations of alleles along the chromosomes = genetic variation in gametes
  2. Independent assortment of homologous chromosomes in metaphase l
    → homologous chromosomes assort themselves randomly along equatorial plane in metaphase l = resultant gametes contain a combination of chromosomes from maternal and paternal
24
Q

differences between meiosis and mitosis (7)

A
  1. Location: Mitosis occurs in normal body cells during growth or repair of body parts but meiosis occurs in gonads during gamete
    formation
  2. no. of chromosomes in daughter cells:
    Mitosis - daughter cells contain same
    number of chromosomes as
    parent cell but in meiosis daughter cells contain half the number of chromosomes as parent cell
  3. genetically identical: in mitosis, daughter cells are genetically dentical to parent cell but in meiosis: daughter cells are not genetically
    identical to parent cell
  4. nuclear divisions: mitosis Involves one nuclear division but meiosis involves two nuclear division
  5. no. of daughter cells: mitosis - 2 daughter cells are produced from one parent cell but in meiosis 4 daughter cells are produced from one parent cell
  6. pairing of homologous chromosomes: Pairing of homologous chromosomes does not occur in mitosis but homologous chromosomes pair at
    prophase I of meiosis
  7. crossing over: No crossing over in mitosis but crossing over may occur at prophase I in meiosis
25
Q

features of homologous chromosomes

A

HCs have the same gene, same shape and same length + same gene location
may have different alleles (version of gene) = can have maternal and paternal chromosome in HC

  • they will still have their own centromere but pair up along their length to form a bigger chromosome

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