A repository of biology-related knowledge.

Everything not otherwise cited was written by the curator of this blog, who is [a high school student] at [a vocational high school] in the United States!

Background illustration made from this image
Reblogged from naturaltypehost  2,319 notes

supaslim:

or, Why Wings Probably Really Evolved

  1. Controlled Falls: Winged dinosaurs were predators, and would have chased or ambushed prey. Wings would allow them to better control pounces and leaps, as well as slow falls from high places that might otherwise injure them.
  2. Wing-Assisted Incline Running: Wings can be used by their owners to help them climb steep hills or tree trunks.
  3. Mantling: Seen in birds of prey even today, wings are useful for hiding prey items from opportunistic passersby who might steal them. Also useful for hiding vulnerable offspring from sight.
  4. Camouflage: Wings can have intricate patterning that help their owners blend into the background, and also help break up their silhouette- particularly important if your predators have poor color vision, like mammals (and mammals were around long before dinosaurs!).
  5. Secondary Sexual Characteristic: Glossy, healthy, bright wings and other feathery appendages are indicators of good health, desirable in mates. It’s an honest signal to females that the male is in good condition and can pass those genes on to the offspring.
  6. Ritualization: The same sexual characteristics can also settle disputes between competing males (or females, if the sexual roles are reversed) without violence. An individual can visually determine if he has a chance in a fight with his opponent without ever fighting. It increases the fitness of both parties.
  7. Deimatic Behavior: This is defensive behavior, or a startle response. Wings can make a bird (or dinosaur) look much larger than they are, and bright colors and bold patterns can startle a predator and deter the attack.
Reblogged from byosis  4 notes

Maximum Likelihood Method

byosis:

Alternative trees are compared with specific models of evolutionary change and the cladogram that is most likely to have produced the observed distribution of character states is identified as the best hypothesis.

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The diagrams can be a little intimidating, but basically, the best tree is the one that is statistically most probable. For example, a model that involves more mutations to produce extant phenotypes is less likely to have occurred.

It’s very similar to the concept of parsimony, but once you get into the complex world of computational phylogeny, the statistical flexibility and such makes this term a bit more meaningful.

Reblogged from naturaltypehost  2,154 notes

sagansense:

paleoillustration:

(3D printing) Darwin’s Cladogram Tree with Finches, by Joaquin Baldwin:

"Charles Darwin’s first ever sketch of a tree of life, in the shape of an actual tree, with finches perched on the branches. Each branch and minute detail of Darwin’s original drawing is represented, and each finch represents the A, B, C and D marks on his sketch. The sketch appeared in his private notebook (“Notebook B on the transmutation of species,” 1837–1838).

If you look carefully, you’ll notice that each finch is slightly different, and the more apart they are from each other in the evolutionary tree, the more distinct the differences are.”

Notes on Mendelian genetics and some inheritance rules. Mendel discovered that there were 2 alleles of each gene that he studied, and every gene that he had studied was on a separate chromosome. We’ll investigate why this is important later.

> Mendel’s Laws: the law of segregation and the law of independent assortment

> Punnett square: a useful tool for figuring out crosses

> The testcross: a useful tool for identifying unknown genotypes based on offspring phenotypes with a homozygous recessive individual

> Other inheritance patterns: incomplete dominance, codominance, multiple alleles, pleiotropy, epistasis, and polygenic inheritance

Some experiments involving plants! These aren’t AP-standard or anything, but if you can grasp the principles that these illustrate, you should have a working understanding of photosynthesis. Most of these experiments involve an iodine test; iodine turns purple-blue when it comes into contact with starch, so if there is any starch present in a leaf because it carried out photosynthesis, for example, the iodine test will turn the leaf black.

1. Plants can only conduct photosynthesis when light is present. The plant in the dark produced no glucose.
2. Plants can only conduct photosynthesis when chlorophyll is present. White parts of the variegated leaf and obscured parts produced no glucose.
3. Plants can only conduct photosynthesis when CO2 is present. When the plant is sealed (with a finite amount of air) with a compound that absorbs CO2, such as KOH, the plant produces no glucose.

The last drawing looks at chlorophyll. It absorbs certain frequencies of light best. I won’t get into the mechanics of how it works here, but basically, the molecule has to absorb energy from light to set off a chain of reactions to store energy for the dark reactions of photosynthesis. It absorbs different frequencies (colors) with different rates of success, and there are different types of chlorophyll on top of that, but the most common type does not absorb green light. That’s why leaves are green, and that’s why the leaf that only receives green light cannot conduct photosynthesis.

Patterns of evolution, part 2

Here’s my first post about convergent, parallel, and coevolution.

Divergent evolution, then, is the development of different traits in related species. There are several types:

> Allopatric speciation = when a population is geographically separated, adapts separately, and divergently evolves into new species.

> Peripatric speciation = when the subgroup is close yet definitely separate from its parent population. It’s often described as allopatric speciation when the group that speciates is very small. The founder effect often comes into play here, meaning that much genetic variety is lost.

> Parapatric speciation = when the subgroup is separate yet still in contact with the main group of the species.

> Sympatric speciation = when a group remains within the main population of a species, adapts, and divergently evolves into a new species.

The oft-cited example of Darwin’s finches is well-used because it explains another slight variation of divergent evolution well: as a species is separated into many different groups that are exposed to different environments and stimuli, the groups adapt and eventually become species in their own right. This phenomenon when species rapidly diverge into many new species is known as adaptive radiation.

... Read more

Patterns of evolution, part 1

Here, I’ll discuss convergent, parallel, and coevolution. Divergent evolution can get a little complicated to explain all at once, so I’ll tackle it in a different post.

Very simply, convergent evolution is the development of similar characteristics in species of different lineages. This is caused by different species living in similar environments, suffering similar pressures, or occupying similar niches.

Parallel evolution can be difficult to distinguish from convergent evolution. Basically, two species of different ancestry evolve in similar ways to adapt to similar pressures. A simple example would be the abundance of plant species with similar leaves, stems, and roots; even though they might not have developed from the same common ancestor, they look very alike.

Finally, coevolution occurs between two species when they adapt with and even because of each other; while the environment can still apply selective pressures on both species, the two apply pressures on each other to adapt as well. Examples include relationships between parasites and hosts (parasites evolve to better parasitize their hosts, while hosts evolve to better defend themselves) and predator and prey (each species gets better at hunting or evading, respectively.)

The cell is actually pretty impressively complicated. The features of a cell can vary drastically between species or even between different tissue types within an organism. Let’s start by looking at a diagram of a typical eukaryotic animal cell, which contains cytoplasm within a plasma membrane. This term refer to both intracellular fluid (or cytosol) and important organelles. For clarity, I’ve only drawn one of each type of organelle, though a real cell could contain more.
A list of organelles labeled in the diagram:
> nucleus: nucleoplasm, nucleolus> endoplasmic reticulum, smooth and rough> Golgi apparatus> secretory vesicle (note: not quite a Golgi vesicle)> ribosome> peroxisome> lysosome> vacuole> mitochondria
Other structures:> plasma membrane> cytoskeleton: centrosome (main microtubule organizing center), microtubule, microfilament
(My handwriting got a little cramped on the right side. The dark maroon colored organelle is the rough endoplasmic reticulum.)

The cell is actually pretty impressively complicated. The features of a cell can vary drastically between species or even between different tissue types within an organism. Let’s start by looking at a diagram of a typical eukaryotic animal cell, which contains cytoplasm within a plasma membrane. This term refer to both intracellular fluid (or cytosol) and important organelles. For clarity, I’ve only drawn one of each type of organelle, though a real cell could contain more.

A list of organelles labeled in the diagram:

> nucleus: nucleoplasm, nucleolus
> endoplasmic reticulum, smooth and rough
> Golgi apparatus
> secretory vesicle (note: not quite a Golgi vesicle)
> ribosome
> peroxisome
>
lysosome
>
vacuole
>
mitochondria

Other structures:
> plasma membrane
> cytoskeleton: centrosome (main microtubule organizing center), microtubule, microfilament

(My handwriting got a little cramped on the right side. The dark maroon colored organelle is the rough endoplasmic reticulum.)