BRAINCAKEDihybrid Crosses
A dihybrid cross follows the inheritance of two characteristics, each controlled by a different gene, at the same time. Here the two genes are on different chromosomes, so they assort independently.
Worked example: in peas, round seeds (R) are dominant to wrinkled (r), and yellow seeds (Y) are dominant to green (y). A pure-breeding round yellow plant (RRYY) is crossed with a wrinkled green plant (rryy). All the F1 are RrYy, round and yellow.
Two F1 plants are crossed: RrYy × RrYy. Each parent makes four gamete types in equal proportions: RY, Ry, rY and ry. A 4 × 4 Punnett square gives 16 equally likely combinations. Collecting the phenotypes gives:
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Key terms in this lesson
- test cross
- A cross between an individual showing a dominant phenotype and a homozygous recessive individual, used to find out if the first is homozygous or heterozygous.
More in Genetic Information
- Law of Segregation
- Law of Independent Assortment
- Multiple Alleles
- Codominance
- Drosophila
- Probability
- Chi-Squared Test
- Chi-Squared Test - Monohybrid Crosses
All 30 lessons in Genetic Information · All Edexcel A-level Biology topics