When limiting factors increase, diversity in populations decreases. In this sense "limiting factors" can be anything from a lack of resources to a lack of food, meaning it's harder for the population to survive.
The process of passing genetic material from one generation to the next depends completely on how cells grow and divide. To reproduce, a simple organism such as bacteria or yeast simply copies its DNA (through a process called replication) and splits in two. But organisms that reproduce sexually go through a complicated dance that includes mixing and matching strands of DNA (a process called recombination) and then reducing the amount of DNA in special sex cells to arrive at completely new genetic combinations for their offspring.
There are two basic kinds of organisms — ones with a nucleus and those without a nucleus (a compartment filled with DNA surrounded by a membrane called a nuclear envelope):
<span>Prokaryotes: Organisms whose cells lack a nucleus and therefore have DNA floating loosely in the liquid center of the cell. Prokaryotes divide, and thus reproduce, by simple mitosis.</span><span>Eukaryotes: Organisms that have a well-defined nucleus to house and protect the DNA. Eukaryotes divide by meiosis for sexual reproduction.</span>
Prokaryotic cells lack a defined nucleus, but have a region in the cell, termed the nucleoid, in which a single chromosomal, circular, double-stranded DNA molecule is located.
