What does it mean when scientist say that living organisms share a universal genetic code

How does the molecular clock work? a. it analyzes the brain functionality of two different species. b. it examines and compares the physical characteristics of two different species. c. it illustrates relationships between two different species. d. it compares the number of mutations that exist in the dna of two different species.

All ova contain sex chromosomes corresponding to: x y xx xy

What is the key to the recognition of codominance?