I'm going for question 3....
DNA (Deoxyribo Nucleic Acid)
is a self-replicating macromolecule which carries the cell's genetic information Inherited characteristics are passed down from parent to offspring mainly in the form of a chemical code. This code is a long - very long - molecule called DNA, found in the cell nucleus.(it is self replicating because the cell has the ability to reproduce precisely the base pair sequence of a DNA molecule using its own machinery of enzymes etc).
Its the structure of DNA that makes it possible to carry a code. It is a double helix, like a spiral staircase, with a sugar-phosphate backbone (the hand rails) and stairs which are formed by paired bases - one attached to the left hand rail, the other attached to the right. There are 4 kinds of bases, and they always pair up A-T and G-C. A length of DNA therefore can be represented as a long sequence like this: AGCTCTATTGCAACTGTGGAATTTCTTAC.....etc
The code can be "read" by specialist enzymes, because it turns out that every 3 letters represents a specific amino acid. For example, AGC might code for alanine, TCT for tyrosine and so on (I've made these up, but you get the idea). A string of amino acids, when joined together, makes a protein.
Proteins are the basis for many of the key chemicals needed by the cell - for example, enzymes are proteins, so a particular stretch of DNA codes for a long string of amino acids. These sequences are translated and turned into proteins, and because most cells contain many millions of DNA base-pairs, this means that they can be turned into a vast number of proteins (or more generally, many different "gene products"
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A gene is a section of DNA which functions as a unit to determine a particular trait and which tends to be inherited as a unit (genes are often defined as "the unit of inheritance"
Each stretch of DNA that codes for an identifiable, specific, product is called a gene. Gene products are proteins (and other molecules) and they are what gives an animal a particular feature or ability (its phenotype). They are usually inherited as a distinct, intact unit, so that parents can pass a specific form of a gene down to their offspring. Some individuals have slight variations in the precise base pair sequences, so you this gives a population some variability, both in it DNA/gene sequence, and in its abilities and features). Like many animals, humans have two copies of every gene (one from our mother and one from our father).
Chromosomes are structures made up of DNA plus structural proteins. Most of the time, our DNA is unravelled because it is being actively transcribed - our cells are constantly busy producing stuff. But shortly before a cell divides, the DNA gets contracted into compact structures called chromosomes. These are simply lengths of DNA, wrapped up in protective and regulatory proteins so that cell division can proceed easily. Every species has a constant number of chromosomes (humans have 46).