The Puffin's Lair - Hot N Cold

There are more than one way to determine the gender in nature. We humans depend on who is the carrier of the Y chromosome - XX female, XY male -. Other species such butterflies or chickens depend on the W chromosome - ZZ male, ZW female. But there is still another surprising possibility: the environmental sex determination.

Temperature plays a key role in a special type of this system, being very common in crocodilians, turtles and other reptiles. This nongenetic way of determine whether an egg develops as male or female occurs after fertilization.

For instance, in some turtle species, like Trachemys, eggs from colder nests result in all males, whereas eggs from warmer nests turn into females. In crocodilian species — the most studied is the American alligator— both low and high temperatures result in females, and intermediate temperatures become males.

Temperature-dependent sex determination in three reptile species: the American alligator (Alligator mississippiensis), the red-eared slider turtle (Trachemys scripta elegans), and the alligator snapping turtle (Macroclemys temminckii). (After Crain and Guillette 1998)

Slight differences

Let's start with general genetics: "What is DNA and what is for?" and "How could we be apparently so different among us but at the same time the same species?"

For answering the first question we will start with the Central Dogma of Molecular Biology:

The DNA is our particular library, essential for life. We have all the necessary information encoded in a combination of four nucleotides (A, T, G and C). This library has hundreds of books, which we are going to call RNA. We have a lot of different kinds of RNA, which maybe is boring and not what you are looking for at this blog. So let's say that this RNA should be translated into proteins to be useful for a cell. These proteins will work independently or as a subunit of a big complex to make what is required.