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

Gametes are the sex cells (e.g. sperm cells and egg cells) that fuse together during sexual reproduction.
Gametes are haploid (have half the number of chromosomes as diploid cells).
When the gametes fuse together, a new diploid organism (an organism with two copies of every chromosome) is created.
An individual inherits one copy of a chromosome from each parent.

Producing gametes

Haploid gametes are produced from diploid cells in an organism.
The gametes are produced in a process called meiosis.

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.

Random fertilisation

Sexual reproduction involves the random fusion between gametes.
Any two gametes could fuse together to produce a random combination of chromosomes.
Meiosis and random fertilisation further increase genetic diversity in this way.

Meiosis

Meiosis is the production of haploid gametes from diploid cells. The steps involved in this process are:

1) Producing sister chromatids

The chromosomes in the cells replicate to produce an identical copy of each other.
- The replicated chromosomes are called chromatids.
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) Arranging the chromosomes

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 centre of the cell.
The chromosomes are moved by fibres called spindle fibres.

3) Separating the chromosomes

The homologous chromosomes are separated and pulled to opposite ends of the cell by the spindle fibres.
The separation of the chromosomes from each pair is random.
Random combinations of chromosomes are pulled to each side of the cell.

4) Cell division (meiosis I)

As the homologous chromosomes are separated, the cell divides into two cells.
One chromosome from a pair is separated into each cell.
This division is called meiosis I.
Meiosis I produces two genetically different cells.

5) Separating sister chromatids

The sister chromatids are separated by the spindle fibres and pulled to opposite ends of the cell.
The separation of the sister chromatids is random.

6) Cell division (meiosis II)

As the sister chromatids are separated, the cell divides into two cells.
One chromatid from a chromosome is separated into each cell.
This division is called meiosis II.
Meiosis II produces four genetically different haploid cells.

Genetic Variation

Meiosis produces four genetically different daughter cells. Genetic variation is generated in each daughter cell in two ways. These are:

Crossing over

The chromosomes of a homologous pair are arranged down the middle of the cell before the first cell division in meiosis I.
Sections of DNA are swapped between the chromosomes in a pair in a process called crossing over.
Crossing over produces new combinations of alleles. This process is a key part of genetic recombination.
- This increases genetic variation.

Independent segregation

The chromosomes in a homologous pair are separated in meiosis I in a random formation to produce two genetically different daughter cells.
The combination of chromosomes in the two daughter cells is random.
The process of separating chromosomes into random combinations is called independent segregation.
Independent segregation increases genetic variation.

1Biological Molecules

1.1Monomers & Polymers

1.1.1Monomers & Polymers

1.1.2Condensation & Hydrolysis Reactions

1.2Carbohydrates

1.2.1Structure of Carbohydrates

1.2.2Types of Polysaccharides

1.2.3End of Topic Test - Monomers, Polymers and Carbs

1.2.4Exam-Style Question - Carbohydrates

1.2.5A-A* (AO3/4) - Carbohydrates

1.3Lipids

1.3.1Triglycerides & Phospholipids

1.3.2Types of Fatty Acids

1.3.3Testing for Lipids

1.3.4Exam-Style Question - Fats

1.3.5A-A* (AO3/4) - Lipids

1.4Proteins

1.4.1The Peptide Chain

1.4.2Investigating Proteins

1.4.3Primary & Secondary Protein Structure

1.4.4Tertiary & Quaternary Protein Structure

1.4.5Enzymes

1.4.6Factors Affecting Enzyme Activity

1.4.7Enzyme-Controlled Reactions

1.4.8End of Topic Test - Lipids & Proteins

1.4.9A-A* (AO3/4) - Enzymes

1.4.10A-A* (AO3/4) - Proteins

1.5Nucleic Acids

1.5.1DNA & RNA

1.5.2Nucleotides

1.5.3Polynucleotides

1.5.4DNA Replication

1.5.5Exam-Style Question - Nucleic Acids

1.5.6A-A* (AO3/4) - Nucleic Acids

1.6ATP

1.6.1Structure of ATP

1.6.2Hydrolysis of ATP

1.6.3Resynthesis of ATP

1.6.4End of Topic Test - Nucleic Acids & ATP

1.7Water

1.7.1Importance of Water

1.7.2Structure of Water

1.7.3Properties of Water

1.7.4A-A* (AO3/4) - Water

1.8Inorganic Ions

1.8.1Inorganic Ions

1.8.2End of Topic Test - Water & Inorganic Ions

2Cells

2.1Cell Structure

2.1.1Introduction to Cells

2.1.2Eukaryotic Cells & Organelles

2.1.3Eukaryotic Cells & Organelles 2

2.1.4Prokaryotes

2.1.5A-A* (AO3/4) - Organelles

2.1.6Methods of Studying Cells

2.1.7Microscopes

2.1.8End of Topic Test - Cell Structure

2.1.9Exam-Style Question - Cells

2.1.10A-A* (AO3/4) - Cells

2.2Mitosis & Cancer

2.2.1Mitosis

2.2.2Stages of Mitosis

2.2.3Investigating Mitosis

2.2.4Cancer

2.2.5A-A* (AO3/4) - The Cell Cycle

2.3Transport Across Cell Membrane

2.3.1Cell Membrane Structure

2.3.2A-A* (AO3/4) - Membrane Structure

2.3.3Diffusion

2.3.4Osmosis

2.3.5Active Transport

2.3.6End of Topic Test - Mitosis, Cancer & Transport

2.3.7Exam-Style Question - Membranes

2.3.8A-A* (AO3/4) - Membranes & Transport

2.3.9A-A*- Mitosis, Cancer & Transport

2.4Cell Recognition & the Immune System

2.4.1Immune System

2.4.2Phagocytosis

2.4.3T Lymphocytes

2.4.4B Lymphocytes

2.4.5Antibodies

2.4.6Primary & Secondary Response

2.4.7Vaccines

2.4.8HIV

2.4.9Ethical Issues

2.4.10End of Topic Test - Immune System

2.4.11Exam-Style Question - Immune System

2.4.12A-A* (AO3/4) - Immune System

3Substance Exchange

3.1Surface Area to Volume Ratio

3.1.1Size & Surface Area

3.1.2A-A* (AO3/4) - Cell Size

3.2Gas Exchange

3.2.1Single-Celled Organisms

3.2.2Multicellular Organisms

3.2.3Control of Water Loss

3.2.4Human Gas Exchange

3.2.5Ventilation

3.2.6Dissection

3.2.7Measuring Gas Exchange

3.2.8Lung Disease

3.2.9Lung Disease Data

3.2.10End of Topic Test - Gas Exchange

3.2.11A-A* (AO3/4) - Gas Exchange

3.3Digestion & Absorption

3.3.1Overview of Digestion

3.3.2Digestion in Mammals

3.3.3Absorption

3.3.4End of Topic Test - Substance Exchange & Digestion

3.3.5A-A* (AO3/4) - Substance Ex & Digestion

3.4Mass Transport

3.4.1Haemoglobin

3.4.2Oxygen Transport

3.4.3The Circulatory System

3.4.4The Heart

3.4.5Blood Vessels

3.4.6Cardiovascular Disease

3.4.7Heart Dissection

3.4.8Xylem

3.4.9Phloem

3.4.10Investigating Plant Transport

3.4.11End of Topic Test - Mass Transport

3.4.12A-A* (AO3/4) - Mass Transport

4Genetic Information & Variation

4.1DNA, Genes & Chromosomes

4.1.1DNA

4.1.2Genes

4.1.3Non-Coding Genes

4.1.4The Genetic Code

4.1.5A-A* (AO3/4) - DNA

4.2DNA & Protein Synthesis

4.2.1Protein Synthesis

4.2.2Transcription & Translation

4.2.3End of Topic Test - DNA, Genes & Protein Synthesis

4.2.4Exam-Style Question - Protein Synthesis

4.2.5A-A* (AO3/4) - Coronavirus Translation

4.2.6A-A* (AO3/4) - Transcription

4.2.7A-A* (AO3/4) - Translation

4.3Mutations & Meiosis

4.3.1Mutations

4.3.2Meiosis

4.3.3A-A* (AO3/4) - Meiosis

4.3.4Meiosis vs Mitosis

4.3.5End of Topic Test - Mutations, Meiosis

4.3.6A-A* (AO3/4) - DNA,Genes, CellDiv & ProtSynth

4.4Genetic Diversity & Adaptation

4.4.1Genetic Diversity

4.4.2Natural Selection

4.4.3A-A* (AO3/4) - Natural Selection

4.4.4Adaptations

4.4.5Investigating Natural Selection

4.4.6End of Topic Test - Genetic Diversity & Adaptation

4.4.7A-A* (AO3/4) - Genetic Diversity & Adaptation

4.5Species & Taxonomy

4.5.1Courtship Behaviour

4.5.2Phylogeny

4.5.3Classification

4.5.4DNA Technology

4.5.5A-A* (AO3/4) - Species & Taxonomy

4.6Biodiversity Within a Community

4.6.1Biodiversity

4.6.2Index of diversity

4.6.3Agriculture

4.6.4End of Topic Test - Species,Taxonomy& Biodiversity

4.6.5A-A* (AO3/4) - Species,Taxon&Biodiversity

4.7Investigating Diversity

4.7.1Genetic Diversity

4.7.2Quantitative Investigation

5Energy Transfers (A2 only)

5.1Photosynthesis

5.1.1Overview of Photosynthesis

5.1.2Photoionisation of Chlorophyll

5.1.3Production of ATP & Reduced NADP

5.1.4Cyclic Photophosphorylation

5.1.5Light-Independent Reaction

5.1.6A-A* (AO3/4) - Photosynthesis Reactions

5.1.7Limiting Factors

5.1.8Photosynthesis Experiments

5.1.9End of Topic Test - Photosynthesis

5.1.10A-A* (AO3/4) - Photosynthesis

5.2Respiration

5.2.1Overview of Respiration

5.2.2Anaerobic Respiration

5.2.3A-A* (AO3/4) - Anaerobic Respiration

5.2.4The Link Reaction

5.2.5The Krebs Cycle

5.2.6Oxidative Phosphorylation

5.2.7Respiration Experiments

5.2.8End of Topic Test - Respiration

5.2.9A-A* (AO3/4) - Respiration

5.3Energy & Ecosystems

5.3.1Biomass

5.3.2Production & Productivity

5.3.3Agricultural Practices

5.4Nutrient Cycles

5.4.1Nitrogen Cycle

5.4.2Phosphorous Cycle

5.4.3Fertilisers & Eutrophication

5.4.4End of Topic Test - Nutrient Cycles

5.4.5A-A* (AO3/4) - Energy,Ecosystems&NutrientCycles

6Responding to Change (A2 only)

6.1Nervous Communication

6.1.1Survival

6.1.2Plant Responses

6.1.3Animal Responses

6.1.4Reflexes

6.1.5End of Topic Test - Reflexes, Responses & Survival

6.1.6Receptors

6.1.7The Human Retina

6.1.8Control of Heart Rate

6.1.9End of Topic Test - Receptors, Retina & Heart Rate

6.2Nervous Coordination

6.2.1Neurones

6.2.2Action Potentials

6.2.3Speed of Transmission

6.2.4End of Topic Test - Neurones & Action Potentials

6.2.5Synapses

6.2.6Types of Synapse

6.2.7Medical Application

6.2.8End of Topic Test - Synapses

6.2.9A-A* (AO3/4) - Nervous Comm&Coord

6.3Muscle Contraction

6.3.1Skeletal Muscle

6.3.2Sliding Filament Theory

6.3.3Contraction

6.3.4Slow & Fast Twitch Fibres

6.3.5End of Topic Test - Muscles

6.3.6A-A* (AO3/4) - Muscle Contraction

6.4Homeostasis

6.4.1Overview of Homeostasis

6.4.2Blood Glucose Concentration

6.4.3Controlling Blood Glucose Concentration

6.4.4End of Topic Test - Blood Glucose

6.4.5Primary & Secondary Messengers

6.4.6Diabetes Mellitus

6.4.7Measuring Glucose Concentration

6.4.8Osmoregulation

6.4.9Controlling Blood Water Potential

6.4.10ADH

6.4.11End of Topic Test - Diabetes & Osmoregulation

6.4.12A-A* (AO3/4) - Homeostasis

7Genetics & Ecosystems (A2 only)

7.1Genetics

7.1.1Key Terms in Genetics

7.1.2Inheritance

7.1.3Linkage

7.1.4Multiple Alleles & Epistasis

7.1.5Chi-Squared Test

7.1.6End of Topic Test - Genetics

7.1.7A-A* (AO3/4) - Genetics

7.2Populations

7.2.1Populations

7.2.2Hardy-Weinberg Principle

7.3Evolution

7.3.1Variation

7.3.2Natural Selection & Evolution

7.3.3End of Topic Test - Populations & Evolution

7.3.4Types of Selection

7.3.5Types of Selection Summary

7.3.6Overview of Speciation

7.3.7Causes of Speciation

7.3.8Diversity

7.3.9End of Topic Test - Selection & Speciation

7.3.10A-A* (AO3/4) - Populations & Evolution

7.4Populations in Ecosystems

7.4.1Overview of Ecosystems

7.4.2Niche

7.4.3Population Size

7.4.4Investigating Population Size

7.4.5End of Topic Test - Ecosystems & Population Size

7.4.6Succession

7.4.7Conservation

7.4.8End of Topic Test - Succession & Conservation

7.4.9A-A* (AO3/4) - Ecosystems

8The Control of Gene Expression (A2 only)

8.1Mutation

8.1.1Mutations

8.1.2Effects of Mutations

8.1.3Causes of Mutations

8.2Gene Expression

8.2.1Stem Cells

8.2.2Stem Cells in Disease

8.2.3End of Topic Test - Mutation & Gene Epression

8.2.4A-A* (AO3/4) - Mutation & Stem Cells

8.2.5Regulating Transcription

8.2.6Epigenetics

8.2.7Epigenetics & Disease

8.2.8Regulating Translation

8.2.9Experimental Data

8.2.10End of Topic Test - Transcription & Translation

8.2.11Tumours

8.2.12Correlations & Causes

8.2.13Prevention & Treatment

8.2.14End of Topic Test - Cancer

8.2.15A-A* (AO3/4) - Gene Expression & Cancer

8.3Genome Projects

8.3.1Using Genome Projects

8.4Gene Technology

8.4.1Recombinant DNA

8.4.2Producing Fragments

8.4.3Amplification

8.4.4End of Topic Test - Genome Project & Amplification

8.4.5Using Recombinant DNA

8.4.6Medical Diagnosis

8.4.7Genetic Fingerprinting

8.4.8End of Topic Test - Gene Technologies

8.4.9A-A* (AO3/4) - Gene Technology

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