Biology

DNA is stored in the nucleus, which determines what each cell will become and how they are arranged. Like instructions to build you!
It stands for deoxyribonucleic acid and is made of sugar, phosphate, and base. It's shaped like a twisted ladder, called a double helix.
The sides of the ladder are alternating suger and phosphate, and the bases are the rungs.

The four bases are adenine, cytosine, thymine, and guanine (abbreviated with their first letter). A pairs with T and C paits with G (think: A Trait Could Grow).

DNA is usually found in chromatin, which coils during cell division to form chromosomes. Women have XX ones and males have XY.
A gene is a part of the DNA that codes for a protein; similar cells form tissues and similar tissues form organs.
Each X or Y chromosome has two chromatids-- these are called sister chromatids, because they're identical. They're connected by the centromere in the middle. In cases where there is only one chromatid, such as after cell division, each chromatid counts as its own chromosome.

Sexual reproduction requires two parents (or one, for self-pollinating plants.), each providing one gamete (sex cell). Thus, there is a genetic mix between parents.

Advantages include:

• Genetic variation; it is easier to adapt and develop new, potentially helpful traits.
• It is easier to breed out undesirable traits.
• Being diverse makes it harder for one genetic disease to wipe out the population.

Some disadvantages are:

• High energy expense; finding a mate is hard!
• Long gestation period
• Smaller population; harder to outcompete competitors

Asexual reproduction is when you clone yourself.

• Large population, can crowd out competitors
• Low energy expenditure; no need to find a mate!

• Overpopulation may lead to offspring competing with each other.
• No genetic diversity; harder to adapt or evolve

There are many forms of asexual reproduction, such as:

• Binary fission (prokaryotes): The DNA and organelles duplicate, and it splits in half.
• Budding (hydra): A small growth develops on the parent, after whihc it falls off and a new organism is formed.
• Fragmentation (planaria): After cutting or losing a part of their body, each part grows into a new creature.
• Vegetative propagation (strawberries): An offshoot from the parent burrows into the ground, supplemented by its parent, and grows into a new plant.
• Spore formation (fungi): Small seed-like structures form that can grow into new organisms.
• Parthogenesis (lizards): Unfertilized eggs develop.

You know when you get a cut and it heals in a few days? You owe that ability to the cell cycle. It's made of three phases: interphase, mitosis, and cytokinesis.
The middle section, mitosis, can be further separated into four phases: prophase, metaphase, anaphase, and telophase. (To remember, you can think PMAT or "Prime Ministers Aren't Trustworthy".)
Here's a diagram to help you.

1. Prophase: Chromatin fibers condense to form visible chromosomes, and the spindle fibers begins to form as centrosomes move to opposite poles.
2. Metaphase: Chromosomes line up along the metaphase plate, the middle of the cell. Each sister chromatid is attached to a spindle fiber.
3. Anaphase: The sister chromatids separate at the centromere and are pulled to opposite poles of the cell.
4. Telophase: Chromosomes arrive at opposite poles, begin to decondense, and new nuclear envelopes form around the two sets of chromosomes.

Meiosis is like mitosis, but doubled. It's used to create gametes, which each have 23 chromosomes instead of 46 (when two join, it forms a full set). Thus, you need to divide twice.
After the first division, there are still 46 chromosomes, but only with one chromatid each. After it is completed there are half as many chromosomes.