A-Level Biology AQA 7402

The genotype is the genetic constitution of an organism.

The phenotype is the expression of this genetic constitution and its interaction with the environment.

There may be many alleles of a single gene.

Alleles may be dominant, recessive or codominant.

In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous.

The use of fully labelled genetic diagrams to interpret, or predict, the results of:

• monohybrid and dihybrid crosses involving dominant, recessive and codominant alleles
• crosses involving sex-linkage, autosomal linkage, multiple alleles and epistasis.

Use of the chi-squared ($\chi^2$) test to compare the goodness of fit of observed phenotypic ratios with expected ratios.