Copies that are not exact
Copying is never perfectly reliable.
A tiny slip
A cell copies its DNA. The copying is done by chemical reactions.
Will every copy be exactly the same as the original?
What this lesson covers
The idea
No biochemical reaction is absolutely reliable, so DNA copies are similar to but may not be identical to the original; drastic variations kill the new cell, and this inbuilt tendency for variation is the basis for evolution.
A tiny slip
A cell copies its DNA. The copying is done by chemical reactions.
Will every copy be exactly the same as the original?
- It may differ a little
- It is always exactly the same
- It is always completely different
Compare the copies
Press Next step. Each block in the picture stands for a piece of the DNA information.
Similar, not identical
No biochemical reaction is absolutely reliable, so each copy of DNA has some variation. A drastic change kills the new cell. A smaller change lets the cell survive. These small differences between cells are the beginning of evolution, which the next chapter discusses.
No biochemical reaction is absolutely reliable, so DNA copies are similar to but may not be identical to the original. Drastic variations kill the new cell. This inbuilt tendency for variation is the basis for evolution.
Notes
DNA copies are similar but may not be identical. Drastic variations kill the new cell. The tendency for variation is the basis for evolution.
Check yourself
Why can a DNA copy differ from the original?
What happens to a newborn cell whose DNA copy cannot work with the cellular apparatus it inherits?
The inbuilt tendency for variation during reproduction is the basis for …
- The cell changes the DNA on purpose to make a new design. The book says variation arises because the copying reactions are not absolutely reliable.
- No biochemical reaction is absolutely reliable — correct. Yes!
- DNA copies are always completely different. The copies are similar to the original, but may not be identical.
- It grows into a bigger cell. Such a newborn cell will simply die, as the book says.
- It passes its variation on to many cells. A cell with a drastic variation dies, so it cannot pass it on.
- It dies — correct. Yes!
- evolution — correct. Yes!
- nutrition. Nutrition is a life process in which an organism takes in food. The book says variation is the basis for evolution.
- respiration. Respiration is a life process. The book says variation is the basis for evolution.