One-quarter of the possible offspring for a cross are homozygous dominant. what genotype do each of the parents have? 1) heterozygous 2)homozygous dominant 3)homozygous recessive 4)homozygous

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.