In some genetically engineered corn plants, a Bt gene was added to a chromosome. The Bt gene specifies a protein called Bt that is lethal to certain flying insect pests that eat the corn plants. If the corn plant is is heterozygous for the Bt gene (one homolog has the introduced Bt gene and the other does not), what proportion of the sperm would carry the Bt gene? Is the presence of the Bt gene (a mutation) dominant or recessive to its absence (the wild type)?