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A-Level EDUQUAS Biology > Component 2: Mitosis and Meiosis > Flashcards

Component 2: Mitosis and Meiosis Flashcards

1
Q

What is mitosis?

A

A type of cell division which produces genetically identical daughter cells with each cell containing the same number of chromosomes as the parent nucleus

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2
Q

What is mitosis needed for?

A
  • Growth
  • Cell replacement and regeneration
  • Asexual Reproduction
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3
Q

Describe processes in interphase in mitosis?

A
  • DNA replicates, chromosomes are not visible as chromatin is still dispersed
  • cell grows in size
  • organelles replicate
  • proteins (e.g. histones) and enzymes are synthesised
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4
Q

Describe prophase in mitosis?

A
  • chromosomes condense (2 chromatids held together by a centromere)
  • nucleolus and nuclear envelope disappear
  • centrioles move to opposite poles of the cell and start to form spindle fibres
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5
Q

Describe metaphase in mitosis?

A
  • chromosomes arrange themselves on the equator of the spindle
  • spindle fibres attach to the chromosomes by their centromeres
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6
Q

Describe anaphase in mitosis?

A
  • centromeres divide in two
  • spindle fibres shorten and pull the chromatids to the opposite poles of the cells, centromere first
  • chromatids now called daughter chromosomes
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7
Q

Describe telophase in mitosis?

A
  • daughter chromosomes reach the poles, then uncoil and lengthen (become chromatin)
  • nuclear envelope and nucleolus reform
  • 2 new nuclei are formed
  • spindle fibres disintergrate
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8
Q

Describe cytokinesis in mitosis?

A
  • DNA appears as chromatin again as chromosomes have uncondensed
  • the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides
  • in animal cells the cytoplasm pinches in
  • in plant cells a cell plate forms
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9
Q

What happens after mitosis and cytokinesis?

A

The cell returns to interphase and continues to grow and perform regular cell activities

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10
Q

What is cancer in terms of mitosis?

A
  • uncontrolled mitosis

- cancerous cells divide repeatedly forming a tumour (an irregular mass of cells)

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11
Q

What does cancer do to the body?

A

cancerous cells prevent normal cells/organs from functioning normally

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12
Q

What are cancers thought to be started by?

A

When changes occur in the genes that control cell division

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13
Q

What is meiosis?

A

cell division that occurs during sexual reproduction when it’s important that haploid gametes are produced

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14
Q

What does meiosis produce?

A
  • four genetically different cells from 2 consecutive divisions (gametes)
  • contain half the original number of chromosomes
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15
Q

Define diploid?

A

Cells or organisms that have two copies of each chromosome in their nuclei, has homologous pairs of chromosomes

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16
Q

Define haploid?

A

A cell or organism that has one set of chromosomes/one copy of each chromosome, doesn’t have homologous pairs of chromosomes

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17
Q

What is the diploid number in human?

A

46 (23 homologous pairs, one from mother and one from father)

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18
Q

What are homologous chromosomes?

A

pair of chromosomes that have the same genes at the same loci (1 maternal and 1 paternal)

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19
Q

What happens in interphase?

A
  • chromosomes are not visible
  • DNA replicates
  • Protein synthesis
  • ATP production
  • new organelles formed
  • mitochondria and chloroplasts replicate
  • nuclear envelope and nucleolus still present
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20
Q

What happens in early prophase I?

A
  • chromosomes condense from chromatin
  • each chromosome consists of 2 sister chromatids held together by a centromere
  • centrioles move to opposite poles of the cell
  • each homologous pair of chromosomes come together to form a bivalent
21
Q

What happens in late prophase I?

A
  • crossing over takes place between the non-sister chromatids in the bivalent
  • the exchange of genetic material (alleles) between homologous chromosomes occurs at the chiasmata forming between chromatids
  • nuclear envelope and nucleolus disappear
22
Q

What happens in metaphase I?

A
  • bivalents arrange themselves on the equator of the spindle
  • spindle fibres attach to centromere
  • chromosomes arrange themselves randomly arrange themselves (random/independent assortment)
23
Q

What happens in anaphase I?

A

spindle attaches to the centromere of each homologous chromosomes and pulls whole chromosomes to opposite poles as spindle fibres shorten

24
Q

What happens in telophase I?

A
  • (in animals cells) organelles and cytoplasm divide (cytokinesis)
  • two new haploid cells are formed (each cell has one copy of each homologous pair)
  • chromosome number per cell is halved
  • chromosomes are genetically different from those in the original cell
  • nuclear envelope reforms
  • plants cells go straight to meiosis II, cytokinesis doesn’t take place
25
Q

What happens in prophase II?

A
  • centrioles replicate
  • new spindle fibres form at right angles to the first
  • nuclear envelope and nucleolus disappear
26
Q

What happens in metaphase II?

A
  • chromosomes align themselves randomly on the equator of the (90º to original)
  • each chromosome is a pair of chromatids
  • this phase produces genetic variation due to the random assortment of chromatids on the equator
27
Q

What happens in anaphase II?

A
  • centromeres divide

- chromatids pulled to opposite poles of the cell by the attached spindles

28
Q

What happens in telophase II?

A
  • cytokinesis begins
  • four haploid cells result
  • each daughter cell produced in genetically different
  • nuclear envelope and nucleolus reappear
  • chromatids lengthen and become chromatin
29
Q

Describe processes that happen to produce genetic variation

A
  • during independent assortment of homologous chromosomes, maternal and paternal chromosomes are mixed up
  • during sexual reproduction, there is a random fusion of haploid gametes to form zygote
  • during crossing over, parts of homologous chromosomes may be exchanged producing new allele combinations
30
Q

Difference between mitosis and meiosis: number of nuclear divisions

A

mitosis: 1 nuclear division
meiosis: 2 nuclear division

31
Q

Difference between mitosis and meiosis: number of cells formed

A

mitosis: 2 daughter cells formed
meiosis: 4 daughter cells formed

32
Q

Difference between mitosis and meiosis: ploidy of parental cells/nuclei

A

mitosis & meiosis: 23 pairs of chromosomes (2n, diploid)

33
Q

Difference between mitosis and meiosis: ploidy of daughter cells/nuclei

A

mitosis: diploid
meiosis: haploid (produces cells with half the original number of chromosomes)

34
Q

Difference between mitosis and meiosis: genetic nature of daughter cells/nuclei

A

mitosis: genetically identical daughter cells formed
meiosis: genetically different daughter cells

35
Q

Difference between mitosis and meiosis: pairing of homologous chromosomes

A

mitosis: no pairing of homologous chromosomes
meiosis: pairing of homologous chromosomes

36
Q

Difference between mitosis and meiosis: crossing over

A

mitosis: no crossing over
meiosis: crossing over occurs

37
Q

Difference between mitosis and meiosis: segregation of homologous chromosomes

A

mitosis: homologous pairs aren’t separated
meiosis: homologous pairs are separated

38
Q

Where is DNA found and what is its function?

A

Found in the nucleus and controls all cell activities

39
Q

What is chromatin?

A

Long and thread-like DNA in a non-dividing cell

40
Q

What is a chromosome?

A
  • doubled, coiled, short DNA in a dividing cell
  • chromosomes only become visible when chromatin condenses prior to cell division
  • the 2 copies of the chromosome are called sister chromatids and are joined at the centromere
41
Q

Why does chromatin condense?

A

DNA changes from chromatin to chromosome for more efficient division

42
Q

What is a chromatid?

A

One of the 2 identical copies of a chromosome, joined at the centromere prior to cell division

43
Q

What is the centromere?

A

Specialised region of a chromosome where 2 chromatids join and to which the microtubules of the spindle attach at cell division

44
Q

What is meant by homologous?

A

The chromosomes in a homologous pair are identical in size and shape and they carry the same gene loci, with genes for the same characteristics.
One chromosome of each pair come from each parent, X and Y are not homologous

45
Q

What are the 4 stages in the cell cycle?

A

Mitosis
G1 phase
S phase
G2 phase

46
Q

What happens in G1 phase?

A
  • first growth phase
  • protein synthesis
  • cytoplasm increases
  • number of organelles increases
47
Q

What happens in S phase?

A

DNA replicates if cell is going to divide

48
Q

What happens in G2 phase?

A
  • second growth phase

- proteins necessary for cell division are synthesised

A-Level EDUQUAS Biology (24 decks)

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