This key facts covers Punnett Squares within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 2 of 9 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 2 of 9
Practice
25 questions
Recall
25 flashcards
Punnett Squares
A Punnett square shows possible offspring from two parents:
Example: Eye colour (Brown = B, Blue = b)
Parent 1: Bb (heterozygous brown)
Parent 2: Bb (heterozygous brown)
| B | b | |
| B | BB | Bb |
| b | Bb | bb |
Result: 3 Brown (BB, Bb, Bb) : 1 Blue (bb) = 3:1 ratio
Probability of blue eyes: 1 in 4 = 25%
Visual: Punnett Squares and Genetic Crosses
Remember: Bb x Bb = 3:1 phenotype ratio | Bb x bb = 1:1 ratio | Dominant allele (capital) masks recessive (lowercase)