The outward expression of a gene?

Answer 1

The outward expression of a gene is determined by the alleles. Alleles come and pairs, and the pairings can be heterozygous or homozygous.

For homozygous (both alleles are the same) phenotypes, the trait you see is the same as the alleles. For example, if both alleles are for a white flower, the flower will be white.

There are different outcomes for heterozygous (one dominant allele, the other recessive) phenotypes. In complete dominance (the most common), the dominant allele is the the trait you see. For example, the flower has an allele for red (dominant) and white (recessive), it will be red because red is dominant to white. In incomplete dominance, the dominant allele is not strong enough to fully cut out the recessive so trait will be a mix of both. In the flower's case, it would be pink because white will be seen through the red. In codominance, both alleles are expressed just on different areas. The flower would have both red and white splotches.