The condition of having gametes of different sizes and shapes is Anisogamy.
Anisogamy is a type of sexual reproduction involving the fusion of two dissimilar gametes that have different sizes and shapes. The male (sperm cell) is considered as the smaller gamete, while the female (egg cell) is considered as the larger gamete. The two gametes may be motile (such as in humans) or non-motile (such as in some algae and plants).
Spread of disease is density dependent because it is more severe the greater the population density as the disease would spread more easily. If there is low population density it would spread slower.
