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Biology Core Idea 2 > Mitosis and Meiosis > Flashcards

Mitosis and Meiosis Flashcards

Describe event during mitotic and meiotic cell cycle and their significance Explain gene mutation and chromosome aberration

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1
Q

Cell division (2)

A
  1. Nuclear division (mitosis and meiosis)

2. Cytokinesis (division of cytoplasmic content)

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2
Q

Chromosome structure

A
  • Deoxyribonucleic acid (DNA)
  • Double-stranded, helical
  • Carries genetic information that codes for protein
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3
Q

Chromatin

A
  • When cell is not dividing
  • Dispersed, uncondensed mass of long, thin, thread-like fibres
  • Complex of DNA + histone proteins → octamer formed by 8 histone proteins forming nucleosomes
  • Condensed by coiling/folding many times upon itself
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4
Q

Sister chromatids

A
  • Identical DNA molecules
  • Replicated from same DNA molecule
  • Held together at centromere (by kinetochore protein)
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5
Q

Diploid

A
  • Describes a nucleus, cell or organism with 2 complete sets of chromosomes → exist as homologous pairs, one from each parent
  • 2n
  • Somatic cells are diploid
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6
Q

Haploid

A
  • Only one complete set of chromosomes
  • One homologue each homologous chromosome pair
  • Gametes are haploid
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7
Q

Homologous chromosomes

A
  • Same size, shape, centromere position, staining pattern - - Same genes
  • But may not be identical → different alleles at the same locus
  • One from male parent other from female parent
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8
Q

Allele

A

Alternative forms of a gene

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9
Q

Cell cycle (2)

A
  1. Interphase (90%)

2. Cell division

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10
Q

Interphase (4)

A
  1. Synthesis and growth
  2. Produce materials and organelles needed to carry out functions
  3. Replicate DNA
  4. Gap phase 1, synthesis phase, gap phase 2
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11
Q

G1 (Gap phase 1) (4)

A

Synthesis of:

  1. Organelles
  2. RNA
  3. Protein
  4. ATP
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12
Q

S (Synthesis phase) (1)

A

DNA molecules replicate (semi-conservative replication) → DNA content doubles

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13
Q

G2 (Gap phase 2) (3)

A

Synthesis of:

  1. Organelles
  2. Spindle proteins (tubulin dimers+polymerisation)
  3. ATP
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14
Q

Mitosis (4)

A
  • Nuclear division
  • 2 daughter nuclei containing identical sets of chromosomes
  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
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15
Q

Prophase (3)

A
  1. Chromatin condenses to form chromosomes, each comprising 2 sister chromatids joined at the centromere
  2. Centrioles move to opposite poles and spindle fibres start to form
  3. Nucleolus disappears and nuclear envelope disintegrates into vesicles
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16
Q

Metaphase (2)

A
  1. Chromosomes align at the metaphase plate

2. Each chromosome is attached to 2 kinetochore microtubules at the centromere (kinetochore protein)

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17
Q

Anaphase (3)

A
  1. Centromere of each chromosome divides → each sister chromatid now known as daughter chromosome
  2. Kinetochore microtubules shorten → pull daughter chromosome, centromere first, to opposite poles
  3. Non-kinetochore microtubules elongate and slide in opposite directions → elongating the cell
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18
Q

Telophase (3)

A
  1. Chromosome decondenses to form chromatin
  2. Spindle fibres disintegrate
  3. Nuclear envelope reforms and nucleolus reappears
19
Q

Cytokinesis (2)

A
  1. Animal cells: cell membrane invaginates towards equator of the cell, forming a cleavage furrow → deepens and is pinched into 2 → 2 daughter cells produced
  2. Plant cells: Fluid-filled vesicles move to metaphase plate of the cell and coalesce to form a cell plate → separate the 2 daughter cells
20
Q

Significance of mitosis (4)

A
  1. Maintain genetic stability → produce genetically identical daughter nuclear with same number and type of chromosomes and the same alleles (semi-conservative replication)
  2. Growth → increase no. of cells
  3. Regeneration and cell replacement → replace damaged cells
  4. Asexual reproduction → produce genetically identical offspring
21
Q

Need for regulation (2)

A
  1. Cell cycle regulated tightly at checkpoints (G₁, G₂, M)
  2. Cancer occurs when dysregulation of checkpoints occurs or cells escape the cell cycle control mechanism that normally regulates their growth → uncontrolled cell division
22
Q

Meiosis

A
  • Produces 4 haploid daughter nuclei
  • Genetically different → variation
  • Involves 2 nuclear divisions
  1. Meiosis I
  2. Meiosis II
23
Q

Meiosis I

A
  • Involves pairing of homologous chromosomes and their subsequent separation into 2 daughter cells → reduce chromosome no. by half
  1. Prophase I
  2. Metaphase I
  3. Anaphase I
  4. Telophase I
24
Q

Meiosis II

A
  • Involves separation of 2 sister chromatids
  1. Prophase II
  2. Metaphase II
  3. Anaphase II
  4. Telophase II
25
Q

Prophase I (5)

A

1-3 → Same as mitosis prophase

  1. Synapsis occurs → homologous chromosomes pair up to form bivalents
  2. Crossing over occurs between non-sister chromatids of homologous chromosomes, forming chiasmata → exchange of corresponding alleles on non-sister chromatids → new combination of alleles
26
Q

Metaphase I (2)

A
  1. Homologous chromosomes align in pairs at the metaphase plate → independent assortment occurs
  2. Each chromosome attached to kinetochore microtubules from the pole it faces
27
Q

Anaphase I (3)

A
  1. Homologues separate to opposite poles
  2. Each pulled by shortening kinetochore microtubules
  3. Same as mitosis anaphase
28
Q

Telophase I

A

1-3 → Same as mitosis telophase

  1. Each pole now has a haploid set of chromosomes
29
Q

Cytokinesis (I)

A

Might happen, might not happen

30
Q

Meiosis II

A

Almost exactly the same as mitosis

31
Q

Cytokinesis (II)

A
  • Cells divide to give a total of 4 daughter cells

- Each possess half the no. of chromosomes as parent cell

32
Q

Significance of meiosis (2)

A
  1. Formation of haploid gametes in sexual reproduction

2. Genetic variation

33
Q

Formation of haploid gametes in sexual reproduction

A
  • Reduction division: produce 4 haploid gametes from 1 diploid parent cell
  • Diploid condition restored during fertilisation
  • Maintains chromosome number in every generation
34
Q

Genetic variation

A
  1. Crossing over between non-sister chromatids of homologous chromosomes during prophase I → new combinations of alleles on chromatids
  2. Independent assortment of homologous chromosomes at metaphase plate and their subsequent separation during metaphase I and anaphase I respectively → gametes with 2^n possible different combinations of maternal and paternal chromosomes
  3. Random orientation of non-identical sister chromatids of each chromosome at the metaphase plate and their subsequent separation during metaphase II and anaphase II respectively → gametes with new combinations of alleles on chromosome
  4. Random fusion of gamete → during sexual reproduction/fertilisation → offspring with a variety of genotypes and possibly phenotypes
35
Q

Types of mutations (2)

A
  1. Gene mutations (under translation)

2. Chromosomal aberration

36
Q

Chromosomal aberration (2)

A
  1. Variation in chromosomal structure

2. Variation in chromosomal number

37
Q

Variation in chromosomal structure

A
  1. Deletion
  2. Duplication
  3. Inversion
  4. Translocation
38
Q

Deletion and duplication

A
  • Remove/repeat chromosomal segment
  • Likely to occur during crossing over → non-sister chromatids of homologous chromosomes break and rejoin at incorrect location → unequal crossover
  • Can result in phenotypic abnormalities due to reduced/additional genes
39
Q

Inversion and translocation

A
  • Reverse/move chromosomal segment
  • Expression of gene influenced by new location
  • Amt of genetic material remains the same
  • Result in disease
40
Q

Variation in chromosomal number

A

Aneuploidy

41
Q

Aneuploidy

A
  • Cell does not have a chromosome number that is a multiple of the haploid number → extra/fewer copies than wild type
  • Result of non-disjunction → aberrant gametes
  • Genetic disorder
42
Q

Non-disjunction

A
  1. Homologous chromosomes do not move properly to opposite poles during anaphase I of meiosis I
  2. Sister chromatids fail to separate properly to opposite poles during anaphase II of meiosis II
  3. During mitosis early in embryonic development
43
Q

Down syndrome (Trisomy 21)

A
  • Extra chromosome 21
  • Body cell has total of 47 chromosomes
  • Non-disjunction during meiosis I
  • Characteristic facial features, short stature, heart defects, susceptibility to respiratory infection and mental retardation
  • Sexually underdeveloped and sterile

Biology Core Idea 2 (9 decks)

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