Mitosis and Meiosis Flashcards
Describe event during mitotic and meiotic cell cycle and their significance Explain gene mutation and chromosome aberration
1
Q
Cell division (2)
A
- Nuclear division (mitosis and meiosis)
2. Cytokinesis (division of cytoplasmic content)
2
Q
Chromosome structure
A
- Deoxyribonucleic acid (DNA)
- Double-stranded, helical
- Carries genetic information that codes for protein
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
4
Q
Sister chromatids
A
- Identical DNA molecules
- Replicated from same DNA molecule
- Held together at centromere (by kinetochore protein)
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
6
Q
Haploid
A
- Only one complete set of chromosomes
- One homologue each homologous chromosome pair
- Gametes are haploid
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
8
Q
Allele
A
Alternative forms of a gene
9
Q
Cell cycle (2)
A
- Interphase (90%)
2. Cell division
10
Q
Interphase (4)
A
- Synthesis and growth
- Produce materials and organelles needed to carry out functions
- Replicate DNA
- Gap phase 1, synthesis phase, gap phase 2
11
Q
G1 (Gap phase 1) (4)
A
Synthesis of:
- Organelles
- RNA
- Protein
- ATP
12
Q
S (Synthesis phase) (1)
A
DNA molecules replicate (semi-conservative replication) → DNA content doubles
13
Q
G2 (Gap phase 2) (3)
A
Synthesis of:
- Organelles
- Spindle proteins (tubulin dimers+polymerisation)
- ATP
14
Q
Mitosis (4)
A
- Nuclear division
- 2 daughter nuclei containing identical sets of chromosomes
- Prophase
- Metaphase
- Anaphase
- Telophase
15
Q
Prophase (3)
A
- Chromatin condenses to form chromosomes, each comprising 2 sister chromatids joined at the centromere
- Centrioles move to opposite poles and spindle fibres start to form
- Nucleolus disappears and nuclear envelope disintegrates into vesicles
16
Q
Metaphase (2)
A
- Chromosomes align at the metaphase plate
2. Each chromosome is attached to 2 kinetochore microtubules at the centromere (kinetochore protein)
17
Q
Anaphase (3)
A
- Centromere of each chromosome divides → each sister chromatid now known as daughter chromosome
- Kinetochore microtubules shorten → pull daughter chromosome, centromere first, to opposite poles
- Non-kinetochore microtubules elongate and slide in opposite directions → elongating the cell
18
Q
Telophase (3)
A
- Chromosome decondenses to form chromatin
- Spindle fibres disintegrate
- Nuclear envelope reforms and nucleolus reappears
19
Q
Cytokinesis (2)
A
- Animal cells: cell membrane invaginates towards equator of the cell, forming a cleavage furrow → deepens and is pinched into 2 → 2 daughter cells produced
- 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
- Maintain genetic stability → produce genetically identical daughter nuclear with same number and type of chromosomes and the same alleles (semi-conservative replication)
- Growth → increase no. of cells
- Regeneration and cell replacement → replace damaged cells
- Asexual reproduction → produce genetically identical offspring
21
Q
Need for regulation (2)
A
- Cell cycle regulated tightly at checkpoints (G₁, G₂, M)
- 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
- Meiosis I
- 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
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
24
Q
Meiosis II
A
- Involves separation of 2 sister chromatids
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
25
Prophase I (5)
1-3 → Same as mitosis prophase
4. Synapsis occurs → homologous chromosomes pair up to form bivalents
5. 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
Metaphase I (2)
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
Anaphase I (3)
1. Homologues separate to opposite poles
2. Each pulled by shortening kinetochore microtubules
3. Same as mitosis anaphase
28
Telophase I
1-3 → Same as mitosis telophase
4. Each pole now has a haploid set of chromosomes
29
Cytokinesis (I)
Might happen, might not happen
30
Meiosis II
Almost exactly the same as mitosis
31
Cytokinesis (II)
- Cells divide to give a total of 4 daughter cells
| - Each possess half the no. of chromosomes as parent cell
32
Significance of meiosis (2)
1. Formation of haploid gametes in sexual reproduction
| 2. Genetic variation
33
Formation of haploid gametes in sexual reproduction
- Reduction division: produce 4 haploid gametes from 1 diploid parent cell
- Diploid condition restored during fertilisation
- Maintains chromosome number in every generation
34
Genetic variation
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
Types of mutations (2)
1. Gene mutations (under translation)
| 2. Chromosomal aberration
36
Chromosomal aberration (2)
1. Variation in chromosomal structure
| 2. Variation in chromosomal number
37
Variation in chromosomal structure
1. Deletion
2. Duplication
3. Inversion
4. Translocation
38
Deletion and duplication
- 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
Inversion and translocation
- Reverse/move chromosomal segment
- Expression of gene influenced by new location
- Amt of genetic material remains the same
- Result in disease
40
Variation in chromosomal number
Aneuploidy
41
Aneuploidy
- 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
Non-disjunction
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
Down syndrome (Trisomy 21)
- 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
