Meiosis and Gamete Formation

Introduction

• Meiosis is the process by which gametes (sex cells) are formed.
• Gametes include sperm and egg cells.
• Gametes are haploid cells, containing half the genetic material of normal cells.
• When two gametes combine, they form a diploid cell, which has the full set of genetic information and can develop into a new organism.

Chromosomes Recap

• Human cells contain chromosomes, which hold genetic information.
• Humans have 23 different types of chromosomes.
• Each type has two copies per cell, one from each parent:
  • Maternal chromosomes (from the mother)
  • Paternal chromosomes (from the father)
• Total of 46 individual chromosomes per cell.

Meiosis Process

Step 1: DNA Replication

• Replicate all DNA in the cell.
• Chromosomes form an X shape with the original chromosome and its copy.

Step 2: Chromosome Pair Alignment

• Chromosomes line up in pairs along the cell center:
  • Each pair consists of a maternal and paternal chromosome.
• The arrangement is random, varying between cells.
• Importantly affects genetic variation in resulting gametes.

Step 3: First Cell Division

• Chromosome pairs are pulled apart.
• Cell splits into two, distributing chromosomes randomly.

Step 4: Second Division

• Chromosomes line up along the center again.
• The two arms of each chromosome are pulled to opposite sides.
• Cells divide into four genetically unique cells.

Result

• Four genetically unique gametes are formed.
• In males, these develop into sperm cells.
• In females, they develop into egg cells.
• Each gamete contains 23 chromosomes.

Fertilization

• Fusion of sperm and egg forms a diploid cell.
• The diploid cell divides by mitosis, becoming an embryo, then a fetus, and finally a fully grown organism.

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