A population that has been isolated, especially a smaller one, could have a high level of homozygosity and therefore not a lot of genetic variation. Gene flow between such populations can increase the level of heterozygosity, and therefore up genetic variation.
Parents: Homozygous brown-eyed (M) -
B B blued-eye (F) -
b b [since blue (b) is recessive then and brown (B) is dominant then
in order for the blue gene to
show the you need double recessive or the brown
gene absent
Offspring:
So based on the Punnett cross then you realize that all the possible of spring carry the
genotype B b and as such the
phenotype brown eyes