Dominant traits r traits in which  one allele has an effect in the heterozygous organism
Recessive the allele has no effect in an heterozygous organism. Eg in a family which as the gene for both tallness n shortness... If all the children born show the gene for tallness I.e they all tall, it means the gene for tallness is dominant cos it can be seen physically while the gene for shortness is recessive cos it doesn't express itself in the presence of another gene