GED Science: Punnett Squares & Genetics Made Simple
By David Chen, M.S. · Updated August 14, 2026
GED Science tests Punnett Squares by asking you to predict probability percentages for offspring genotypes and phenotypes. You must know dominant (represented by capital letters, e.g. 'B') versus recessive traits (lowercase, e.g. 'b'), homozygous (BB or bb), and heterozygous (Bb) pairings.
Genetics and heredity questions appear frequently on the GED Science test. Among these, Punnett squares are the #1 calculation question students struggle to complete accurately under timed conditions.
The great news is that Punnett squares follow straightforward 2x2 grid math. Once you memorize a few key vocabulary terms, you can solve any GED genetics question in under 30 seconds.
Essential Genetics Vocabulary for GED Science
- Allele: A variation of a gene (e.g. brown eyes allele 'B' vs blue eyes allele 'b').
- Dominant Trait: Trait that masks recessive alleles. Expressed if at least one capital letter is present (BB or Bb).
- Recessive Trait: Trait only expressed if TWO lowercase alleles are present (bb).
- Homozygous: Having two identical alleles (Homozygous Dominant = BB, Homozygous Recessive = bb).
- Heterozygous: Having two different alleles (Bb).
- Genotype: The genetic code (e.g. 25% BB, 50% Bb, 25% bb).
- Phenotype: The physical appearance resulting from the code (e.g. 75% Brown Eyes, 25% Blue Eyes).
Cross two heterozygous parents (Bb x Bb):
• Top Left Box: B x B = BB (25%)
• Top Right Box: B x b = Bb (25%)
• Bottom Left Box: B x b = Bb (25%)
• Bottom Right Box: b x b = bb (25%)
Result: 75% chance of dominant phenotype, 25% chance of recessive phenotype.
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