It was pollution from the industrial revolution that caused tree trunks to turn from light to dark in color.
Answer: The probability of having an offspring with type A blood is 1/4.
Explanation: Since each of the parents have a recessive allele for blood type O, their genotypes are IAi and IBi for the father and mother respectively. A cross between them will produce four offsprings: one with type AB blood, one with type A blood, one with type B blood and one with type O blood.
See the attached punnet square for more information
The obvious choice would be the hox gene.
Earth's atmosphere is composed of air. Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components.