|The first generation of offspring (first Flial generation) from a cross between two individuals homozygous for contrasting alleles. In this case the F1 must necessarily be heterozygous for the gene under investigation and the phenotypes are consequently similar . The F1 generation thus shows far less variation than subsequent generations (see F2 generation ) in which segregation becomes apparent. The term F1 is also commonly, though incorrectly, used to mean the offspring produced from unspecified parents. See also F1 hybrid.