Punnett Squares 2
Biology: AQA GCSE Higher, topic 6.1.18
Punnett Square
Punnett Squares are used to calculate the ratio of offspring phenotypes.
Dominant alleles
- Pea plants can be either green or yellow.
- The green colour allele is dominant over the yellow allele.
- We represent the dominant green allele with 'G'.
Recessive
- The yellow colour allele is recessive.
- We represent the recessive yellow allele with 'g' on a Punnett square.
Offspring
- With one homozygote recessive parent and one heterozygote parent (shown above):
- There is a 50% chance of offspring being yellow.
- Ratio of green:yellow offspring will be 1:1
Test yourself on Punnett Squares 2
What is the probability (%) of dominant phenotype in the offspring of parents with genes GG and gg?
What is the probability (%) of recessive phenotype in the offspring of parents with genes Gg and Gg?
What is the ratio of green to yellow offspring produced by crossing a heterozygous green pea plant (Gg) with a homozygous recessive yellow pea plant (gg)?
What is the probability (%) of yellow offspring produced by crossing two homozygous recessive (gg) pea plants?
What is the genotype ratio (GG : Gg : gg) of the offspring produced by crossing two heterozygous (Gg) pea plants?