Some traits in genetics show up more often because of something called dominance.

1. Dominant and Recessive Alleles:

   • A dominant allele shows up in the trait if there is at least one copy of it. We can call it "A."
   • A recessive allele needs two copies to show up, which we can call "a."

2. Genotypic Ratios:

   • In a simple cross between two plants, both having one dominant and one recessive allele (Aa x Aa), we get a genotypic ratio of 1:2:1. This means:
     • 1 part will be AA (two dominant alleles)
     • 2 parts will be Aa (one dominant and one recessive allele)
     • 1 part will be aa (two recessive alleles)
   • For traits we can actually see (the phenotypic ratio), it’s about 3:1. This means the dominant traits show up 75% of the time in the offspring.

3. Statistics:

   • Around 80% of human traits follow the rules set by a scientist named Mendel.

Understanding how dominance works helps us see why some traits are more common than others.