non-disjunction is a pathological event that occurs during the second anaphase in meiosis when sister chromatids are not separated. As a result one of the resulting cells will have 1 extra chromosome and the other will be 1 short. An example of a non-disjunction that can occur in humans is Down syndrome that has a frequency of about 1/1000 people. It is caused by the non-disjunction of the 21st pair of chromosomes.
 
        
             
        
        
        
Answer:
A. An area with low air pressure
Explanation:
The red "L" symbol is used to mark an area with a low pressure air system. A low air pressure system would cause thunderstorms, but the "L" does not mean that the area marked would cause a tornado.
Option A should be the correct answer. 
 
        
             
        
        
        
Answer:
1. Double helix is the description of the structure of a DNA molecule. A DNA molecule consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating groups of sugar (deoxyribose) and phosphate groups.
2. The DNA double helix. The two sides are the sugar-phosphate backbones, composed of alternating phosphate groups and deoxyribose sugars. The nitrogenous bases face the center of the double helix.
3. A nucleotide is an organic molecule that is the building block of DNA and RNA. ... A nucleotide is made up of three parts: a phosphate group, a 5-carbon sugar, and a nitrogenous base. The four nitrogenous bases in DNA are adenine, cytosine, guanine, and thymine.
4. A nucleotide is made up of three parts: a phosphate group, a 5-carbon sugar, and a nitrogenous base. The four nitrogenous bases in DNA are adenine, cytosine, guanine, and thymine.
5. In genetics, the term junk DNA refers to regions of DNA that are non-coding. Some of this noncoding DNA is used to produce noncoding RNA components such as transfer RNA, regulatory RNA and ribosomal RNA 
Hopes this helps.
 
        
             
        
        
        
I would think that an unweathered rock would be jagged while a weathered rock would be smooth because of water/wind or what ever weathered it.