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Edexcel iGCSE Biology-4.32 Diploid vs Haploid- Study Notes- New Syllabus

Edexcel iGCSE Biology-4.32 Diploid vs Haploid- Study Notes- New syllabus

Edexcel iGCSE Biology-4.32 Diploid vs Haploid- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.

Key Concepts:

4.32 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23

Edexcel iGCSE Biology-Concise Summary Notes- All Topics

Chromosome Numbers in Humans

📝 Introduction

  • Human cells contain a fixed number of chromosomes that carry genetic information.
  • These chromosomes are present in pairs in body cells and single sets in sex cells.
  • The number of chromosomes changes depending on the type of cell (body cell or gamete).
  • This is important for understanding growth, reproduction, meiosis and fertilisation.
  • In humans, chromosome number is either diploid (46) or haploid (23).

🧬 What are Chromosomes?

  • Chromosomes are thread-like structures made of DNA.
  • They carry genes, which control characteristics like eye colour, height, blood group, etc.
  • Humans have a fixed number of chromosomes in each cell.

Diploid Number (2n = 46)

What is Diploid?

  • A diploid cell contains two sets of chromosomes.
  • One set comes from the mother and one from the father.
  • These chromosomes exist in pairs.

Human Diploid Number

  • In humans: 46 chromosomes = 23 pairs
  • Written as: 2n = 46

Where are Diploid Cells Found?

  • All body (somatic) cells are diploid.

Examples:

  • Skin cells
  • Muscle cells
  • Liver cells
  • Nerve cells

Key Point

  • Diploid cells contain full genetic information needed for body functions.

Haploid Number (n = 23)

What is Haploid?

  • A haploid cell contains only one set of chromosomes.
  • These chromosomes are not in pairs.

Human Haploid Number

  • In humans: 23 chromosomes
  • Written as: n = 23

Where are Haploid Cells Found?

  • Only in sex cells (gametes):
  • Sperm cells (male)
  • Egg cells (female)

Key Point

  • Haploid cells carry half the genetic information of a body cell.

🔄 Why Do Gametes Have Half the Number of Chromosomes?

  • Gametes are formed during a special type of cell division called meiosis.
  • Meiosis reduces the chromosome number from diploid (46) to haploid (23).
  • This is important so that:
  • When fertilisation happens, chromosome number is restored.
  • The offspring gets a correct full set of chromosomes.

🧬 Fertilisation and Chromosome Number

During fertilisation:

  • Sperm (23 chromosomes) + Egg (23 chromosomes)

Forms a zygote with 46 chromosomes (diploid)

Result:

  • 23 + 23 = 46
  • Diploid number is restored in the new organism.

📊 Summary Table

FeatureDiploid CellsHaploid Cells
Chromosome number46 (2n)23 (n)
ChromosomesPairedSingle set
Found inBody cellsGametes (sperm & egg)
FunctionGrowth, repair, body functionsReproduction
Example cellsSkin, muscle, liverSperm, egg

🌟 Key Points to Remember

  • Humans have 46 chromosomes in body cells (diploid).
  • Humans have 23 chromosomes in sex cells (haploid).
  • Diploid = two sets of chromosomes (2n = 46).
  • Haploid = one set of chromosomes (n = 23).
  • Gametes are haploid so that fertilisation restores the correct chromosome number.
  • Fertilisation forms a diploid zygote (46 chromosomes).
  • This balance keeps chromosome number constant across generations.

📝 Quick Recap
Humans: 2n = 46 (body cells), n = 23 (gametes).
Fertilisation restores diploid number: 23 + 23 = 46.
23 pairs → 22 autosomes + 1 sex chromosome pair.

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