Answer:
I think you're referring to the Metaphase...
Explanation:
During Cell Division (or, rather before!) the DNA needs to be replicated. This normally is done by DNA Polymerase, and results in two identical double strands (the "Sister Chromatids".
These chromatids are held together at the Centromere, which will be the heart of the "X"-shape. After that the DNA is packed into Chromosomes by winding it around proteins called Histones. If I remember correctly there are 5 different Histones.
This "Zipping Up" makes the chromosomes more visible.
As the two sister chromatids are still connected, the result is the X-shaped Metaphase Chromosome....
Explanation:
purines-Double carbon-nitrogen ring with four nitrogen atoms
pyrimidines-Single carbon-nitrogen ring with two nitrogen atoms
Answer:
Sources of study of interior of earth:
Deep ocean drilling reveals humongous information through analysis of materials collected at different depth.
Volcanic eruption deliver information by the means of molten magma that comes out of Earth’s interiors.
Surface rocks are readily available earth material.
