Answer:
A gene is a section of a double-stranded molecule known as DNA. This molecule is found within the nucleus of the cell, contained in threadlike structures called chromatin. The two strands form a double helix linked by a series of paired bases. The base adenine is always linked to thymine and the base cytosine is always linked to guanine.
 
        
             
        
        
        
Answer:
Directly counting blood cells or tissue cells by using a hemocytometer can determine the concentration of a known volume. Counting the number of colonies that arise on a pour plate can calculate the concentration by multiplying the count by the volume spread on the pour plate.
 
        
             
        
        
        
Beginning in the mid 1600's Earth entered into a mini-ice age. 1815 was known as the "year without a summer" and snow fell in many European countries during the summer months. The prolonged climate change is attributed to low sun spot activity, while the summer snow is believed to be the result of
A major volcanic eruption.
        
             
        
        
        
When a lineage splits into multiple line of descents, then, it leads to speciation. It is a process by which a single population evolves into different species.  The process of speciation leads to the development of two or more species as  the lineages are splitted. These two evolved species are genetically independent.
Hence, the blank can be filled with 'speciation'.