A good index fossil is one with four characteristics: it is distinctive, widespread, abundant, and limited in geologic time. Because most fossil-bearing rocks formed in the ocean, the major index fossils are marine organisms
Answer:
There will be 12 chromosomes
Explanation:
We have given that The epithelial cells in the skin of an animal have 24 chromosomes
We have to find the number of chromosomes present in the gametes of this animal
We know that number of chromosomes present in the gametes is given by

So number of chromosomes in gametes 
C. Law of segregation is the Mendel's law that states that gametes carry one allele for each trait.