Answer: (A) the time that two species have been evolving independently.
Explanation: The molecular clock is figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when<u> two or more life forms.</u>
Scientists first discovered chromosomes in the nineteenth century, when they were gazing at cells through light microscopes. But how did they figure out what chromosomes do? And how did they link chromosomes — and the specific genes within them — to the concept of inheritance? After a long period of observational studies through microscopes, several experiments with fruit flies provided the first evidence.
What is a gene?
Physically, a gene is a segment (or segments) of a chromosome. Functionally, a gene can play many different roles within a cell. Today, most scientists agree that genes correspond to one or more DNA sequences that carry the coding information required to produce a specific protein, and that protein in turn carries out a particular function within the cell. Scientists also know that the DNA that makes up genes is packed into structures called chromosomes, and that somatic cells contain twice as many chromosomes as gametes (i.e., sperm and egg cells).
But what were the key scientific discoveries that helped establish these principles? As it turns out, the connections between genes, chromosomes, DNA, and heredity were not recognized until long after researchers caught their initial glimpse of chromosomes. The following sections present an abbreviated summary of the major discoveries that revealed these connections.
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There are 4 stages in Mitosis...
Prophase:
It is the first phase in which the chromatin coil to become chromatids, and those chromatids pair up and the nuclear membrane surrounding them dissolves. The centrioles move to each end (pole) of the cell.
Metaphase:
Where the paired chromatids align in the centre of the cell and spindle fibres attach to them at the centromere.
Anaphase:
The centrioles act as anchors, tearing the paired chromatids away from each other using the spindle fibres. Each paired chromatid moves to either (the opposite) end of the cell.
Telophase:
Where the chromatids elongate to form chromatin, and a nuclear membrane begins to form around the chromatin at each end of the cell. Cytokinesis occurs in this stage as the cell separates into two daughter cells. In animal cells, there is cleavage as the two cells are starting to separate. In plant cells, a plate begins to form.