16.1.1
Meiosis
Role of Meiosis
Role of Meiosis
Meiosis is the process that produces haploid gamete cells from diploid cells. Meiosis is necessary for sexual reproduction to take place.


Sexual reproduction
Sexual reproduction
- Gametes are the sex cells (e.g. sperm cells and egg cells) that fuse together during sexual reproduction.
- Gametes are haploid (contain one chromosome).
- When the gametes fuse together, a new diploid organism (an organism with two copies of every chromosome) is formed.
- An individual inherits one copy of a chromosome from each parent.
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Producing gametes
Producing gametes
- Haploid gametes are produced from diploid cells in an organism.
- The gametes are produced in a process called meiosis.
- Meiosis involves two sequential cell divisions (meiosis I and meiosis II).
- In humans, meiosis is used to produce sperm and egg cells.
- In plants, microspore cells divide by meiosis to produce pollen grains (plant gametes).


Genetic variation
Genetic variation
- Meiosis produces four genetically different daughter cells.
- Each daughter cell receives a different combination of chromosomes.
- Meiosis increases genetic diversity in this way.
Meiosis
Meiosis
Meiosis is the production of haploid gametes from diploid cells. The steps involved in this process are:


1) Interphase + prophase 1
1) Interphase + prophase 1
- Interphase:
- The chromosomes in the cells replicate to produce an identical copy of each other.
- The replicated chromosomes are called chromatids.
- Prophase 1:
- The chromatids condense to form a double-armed chromosome. Each arm is made from one chromatid and is joined by a centromere.
- Each arm is called a sister chromatid.


2) Metaphase 1
2) Metaphase 1
- Chromosomes in diploid organisms are found in homologous pairs (chromosomes with identical genes but different alleles).
- The chromosomes in a pair are arranged in the center of the cell.
- The chromosomes are moved by fibers called spindle fibers.


3) Anaphase 1 + telophase 1
3) Anaphase 1 + telophase 1
- Anaphase 1:
- The homologous chromosomes are separated and pulled to opposite ends of the cell by the spindle fibers.
- The separation of the chromosomes from each pair is random.
- Telophase 1:
- Random combinations of chromosomes are pulled to each side of the cell.


4) Cytokinesis (end of meiosis 1)
4) Cytokinesis (end of meiosis 1)
- As the homologous chromosomes are separated, the cell divides into two cells.
- One chromosome from a pair is separated into each cell.
- This division concludes meiosis 1.
- Meiosis 1 produces two genetically different cells.


5) Prophase 2 + metaphase 2
5) Prophase 2 + metaphase 2
- Prophase 2:
- The chromatids condense again.
- Metaphase 2:
- Chromosomes line up in the center of the cell.


6) Anaphase 2
6) Anaphase 2
- Anaphase 2:
- The sister chromatids are separated by the spindle fibers and pulled to opposite ends of the cell.
- The separation of the sister chromatids is random.
7) Telophase 2 + cytokinesis
7) Telophase 2 + cytokinesis
- As the sister chromatids are separated, the cell divides into two cells.
- One chromatid from a chromosome is separated into each cell.
- This division concludes meiosis 2.
- Meiosis 2 produces four genetically different haploid cells.
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
Jump to other topics
1Cell Structure
1.1Cell Structure
1.1.1Studying Cells - Microscopes
1.1.2Introduction to Eukaryotic & Prokaryotic Cells
1.1.3Ultrastructure of Eukaryotic Cells
1.1.4Ultrastructure of Eukaryotic Cells 2
1.1.5Ultrastructure of Eukaryotic Cells 3
1.1.6Prokaryotic Cells
1.1.7Viruses
1.1.8End of Topic Test - Cell Structure
1.1.9Exam-Style Question - Microscopes
1.1.10A-A* (AO2/3) - Cell Structure
2Biological Molecules
2.1Testing for Biological Modules
2.2Carbohydrates & Lipids
2.3Proteins
3Enzymes
4Cell Membranes & Transport
4.1Biological Membranes
5The Mitotic Cell Cycle
6Nucleic Acids & Protein Synthesis
6.1Nucleic Acids
7Transport in Plants
8Transport in Mammals
8.1Circulatory System
8.2Transport of Oxygen & Carbon Dioxide
9Gas Exchange
9.1Gas Exchange System
10Infectious Diseases
10.1Infectious Diseases
10.2Antibiotics
11Immunity
12Energy & Respiration (A2 Only)
13Photosynthesis (A2 Only)
14Homeostasis (A2 Only)
14.1Homeostasis
14.2The Kidney
14.3Cell Signalling
14.4Blood Glucose Concentration
14.5Homeostasis in Plants
15Control & Coordination (A2 Only)
15.1Control & Coordination in Mammals
15.1.1Neurones
15.1.2Receptors
15.1.3Taste
15.1.4Reflexes
15.1.5Action Potentials
15.1.6Saltatory Conduction
15.1.7Synapses
15.1.8Cholinergic Synnapses
15.1.9Neuromuscular Junction
15.1.10Skeletal Muscle
15.1.11Sliding Filament Theory Contraction
15.1.12Sliding Filament Theory Contraction 2
15.1.13Menstruation
15.1.14Contraceptive Pill
15.2Control & Co-Ordination in Plants
16Inherited Change (A2 Only)
16.1Passage of Information to Offspring
16.2Genes & Phenotype
17Selection & Evolution (A2 Only)
17.2Natural & Artificial Selection
18Classification & Conservation (A2 Only)
18.1Biodiversity
18.2Classification
19Genetic Technology (A2 Only)
19.1Manipulating Genomes
19.2Genetic Technology Applied to Medicine
19.3Genetically Modified Organisms in Agriculture
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