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Alevel Biology > Mitosis & Meiosis > Flashcards

Mitosis & Meiosis Flashcards

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1
Q

Define diploid

A

2 complete sets of chromosomes that exist as homologous pairs, where each chromosome of the pair comes from either parent

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2
Q

Define haploid

A

1 complete set of chromosomes, half the diploid no. of chromosomes, contains 1 homologue of each homologous chromosome pair

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3
Q

Define homologous chromosomes

A

A pair of chromosomes, one of paternal and one of maternal origin, which have the same genes at the same gene loci, but may have different alleles; similar in size, shape, centromere position & staining pattern

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4
Q

Definition and role of centromere?

A

seq of non-coding DNA region of chromosome made up of tandem repeats

  1. Allowing sister chromatids to adhere to each other
  2. Allow kinetochore proteins & subsequently kinetochore microtubules to attach→ bivalents can be aligned along metaphase plate during MI of meiosis + chromosomes aligned singly along metaphase plate during M/MII of meiosis→ kinetochore microtubules shorten and separate them to opposite poles during A/AI/AII
    ⇒ allows proper alignment and segregation of chromosomes
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5
Q

Define mitosis/replicative division.

A

nuclear division; produces 2 daughter nuclei containing identical sets of chromosomes as parental cell nucleus

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6
Q

Define meiosis/reduction division.

A

nuclear division; produces daughter nuclei containing half the number of chromosomes as the parent cell nucleus

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7
Q

What happens during interphase?

A

G1: intensive synthesis of organelles, protein etc (growth)
Synthesis phase, S: DNA replication via semi-conservative replication→ DNA content/mlcs of cell doubles→ genetically identical sister chromatids
Gap phase 2, G2: intensive synthesis of organelles, spindle proteins, ATP etc. (growth & prep for mitosis)

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8
Q

What happens during prophase of mitosis?

A
  1. Centrioles move to opposite poles and spindle fibres begin to form
    In late prophase: Kinetochore/Non-kinetochore microtubules extend from each pole towards kinetochores on centromere/middle region of cell and overlap
  2. Chromatin condenses (coils, shortens, thickens) to form chromosomes→ prevent entanglement and breakage of DNA mlc when sister chromatids are separated during anaphase
  3. Nucleolus disappears, nuclear envelope disintegrates into vesicles→ allow kinetochore microtubules to attach to centromere/ allow chromosomes to move to metaphase plate
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9
Q

What happens during prophase I of meiosis?

A
  1. centrioles move to opp poles, spindle fibres form
    Late: kinetochore/non-kinetochore microtubules move to kinetochore on centromere/middle region of cell and overlap
  2. chromatin condenses into chromosomes
  3. nucleolus disappear, nuclear envelope disintegrates
  4. Synapsis: homologous chromosomes pair up→ bivalents/tetrads
  5. Crossing over of corresponding segments of non-sister chromatids of homologous chromosomes, forming chiasma: equivalent portions of chromatids break and rejoin→ exchange of corresponding alleles→ new combination of alleles on chromosome→ genetic variation
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10
Q

What happens during metaphase of mitosis?

A
  1. Kinetochore microtubules from both poles attach to chromosome centromere→ position chromosomes along metaphase plate
  2. Chromosomes aligned singly at metaphase plate
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11
Q

What happens during metaphase I of meiosis?

A
  1. Each homologue’s centromere is attached to kinetochore microtubules from the pole it faces
  2. Pairs of homologues align along metaphase plate
  3. *Independent assortment of homologous chromosomes at metaphase plate: arrangement of 1 pair of homologues at metaphase plate is independent of arrangement of other pairs of homologues
    → + their subsequent separation in AI (chromosomes of one homologous pair separate independently of other pairs to form daughter cells)
    → Diff combinations of maternal and paternal chromosomes in daughter cells at end of meiosis
    → 2^n possible combinations of gametes, n = no. of homologous pairs (assume no crossing over)
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12
Q

What happens during anaphase of mitosis?

A
  1. Non-kinetochore microtubules elongate and slide in opposite direction→ 2 poles move further apart, cell elongates
  2. Centromere divides & kinetochore microtubules shorten→ separated sister chromatids, now called daughter chromosomes, pulled to opposite poles w centromeres leading
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13
Q

What happens during anaphase I of meiosis?

A
  1. Non-kinetochore microtubules elongate and slide in opposite direction→ 2 poles move further apart, cell elongates
  2. Homologues separate towards opposite poles, each pulled by a shortening kinetochore microtubules→ diff combinations of parental chromosomes in gametes
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14
Q

What happens in telophase/telophase I of mitosis/meiosis?

A
  1. spindle fibres disintegrate
  2. daughter chromosome reach pole of cell, decondense and lengthen into chromatin
  3. nucleolus reappears & nuclear envelope reforms around chromatin at each pole of cell→ enclose chromosomes inside nucleus
  4. (not impt) cleavage furrow (animal) or cell plate (plants) starts to form
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15
Q

What happens during cytokinesis?

A
  • Animal: cell membrane invaginates towards equator of cell→ cleavage furrow, which deepens until parent cell pinched into two→ 2 daughter cells
  • Plants (higher plants): fluid-filled vesicles (from GA) move to the metaphase plate of cell & fuse→ cell plate→ 2 daughter cells
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16
Q

What happens during prophase II of meiosis?

A
  1. Centrioles move to opposite poles, spindle fibres form
    Late: and spindle fibres begin to form
    In late prophase: Kinetochore/Non-kinetochore microtubules extend from each pole towards kinetochores on centromere/middle region of cell and overlap
    (not impt) asters: shorter microtubules extending from centrosome
  2. Chromatin condenses (coils, shortens, thickens) to form chromosomes. Each chromosome = 2 sister chromatids, joined at the centromere→ prevent entanglement and breakage of DNA mlc when sister chromatids are separated during anaphase
  3. Nucleolus disappears, nuclear envelope disintegrates into vesicles→ allow kinetochore microtubules to attach to centromere/ allow chromosomes to move to metaphase plate
17
Q

What happens during metaphase II of meiosis II?

A
  1. kinetochore microtubules from both poles attach to centromere of chromosome
  2. chromosomes aligned singly along metaphase plate
  • *Independent/Random orientation of non-identical sister chromatids of each chromosome at metaphase plate (& their subsequent separation at AII) → new combination of alleles & genetic variation
18
Q

Describe the significance of the mitotic cell cycle in maintaining genetic stability.

A

Interphase, S phase: semi-conservative DNA replication, where each strand act as a template for synthesis of complementary strand⇒ formation of chromosomes with genetically-identical sister chromatids

M: chromosomes align singly at equator. A: centromere divides, kinetochore microtubules from either pole attach to each sister chromatids, shorten, separating genetically identical sister chromatids to opposite poles⇒ ensuring equal distribution of chromosomes

New daughter nuclei produced from mitosis have same no. & type of chromosomes w same alleles as parental nuclei→ genetically identical to parent cell

Because of this, genetically identical cells can be produced for…
- Growth: increase in no. of cells
- Regeneration and cell replacement: when damaged tissues are repaired, damaged cells are replaced by cells that are genetically identical to the original; regeneration of missing parts
- Asexual reproduction: produces genetically identical offspring

19
Q

Why is asexual reproduction advantageous?

A

In stable, favourable env where offspring receive the same set of genes from parents who survived and reproduced under the same conditions→ offspring equally well-adapted to the same conditions that allowed the parent to thrive. In ideal conditions, population reproduce very rapidly

Only one parent needed to produce offspring.

20
Q

Describe the significance of meiosis in the formation of haploid gametes and maintaining chromosome no. in every generation.

A

Meiosis produces 4 haploid gametes from 1 diploid parent cell for sexual reproduction: chromosome number halved so that when
fertilisation occurs→ haploid nuclei of male and female gametes fuse to produce a zygote with a diploid no. of chromosomes→ diploid chromosome no. restored
Ensure the same no. of chromosomes in the new adult organism→ chromosome no. in each species is kept the same after many generations

21
Q

Describe the significance of meiosis in introducing genetic variation.

A

Crossing over (PI) + Independent assortment of chromosomes (MI) + subsequent separation of chromosomes at AI + Independent/Random orientation (MII) + subsequent separation (AII) (add details)
⇒ haploid gametes genetically diff from parent
(mutations/nondisjunction also introduces variation)

Random fusion of genetically diff, haploid gametes during fertilisation in sexual reproduction→ genetic variation: greater no. of genotypic combis of a zygote

Importance:
- Some indivs in the population have diff phenotypes
- When env change, some individuals in population may hv favourable characteristics that allow them to survive in the new environment, better adapted to change than others, selected for. Those wout favourable characteristics selected against, die.
- Prevents species from going extinct when env changes

Alevel Biology (16 decks)

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