1. HOW BIOLOGIST CLASSIFY ORGANISMS
*Biologist classify organisms based on appearance, structure, breeding patterns, and similarities in DNA sequence.

2. I. What is a Species?
species – a group of natural populations that are interbreeding
reproductive isolation – occurs when two or more groups of organisms can no longer interbreed; theoretically, two different species cannot interbreed with one another

3. In nature, however, reproductive barriers between sexually reproducing species are not always complete. Sometimes individuals of different species interbreed and produce offspring called hybrids. (ex: dogs-wolves) Many species of plants, some mammals, and many fish are able to form fertile hybrids with one or few closely related species.

4. Dog-Wolf Hybrid Wolves and dogs can produce fertile offspring. Genus

5. Donkey and Horse Hybrid
The offspring of a donkey and a horse is a mule. The mule, however, is sterile.
Donkey:
Equus asinus
Horse:
Equus caballus

6. II. Evolutionary Histories
A. Phylogeny – the evolutionary history of an organism or taxonomic group
Phylogenies can be shown as branching tree diagrams.
The most common method used to make evolutionary trees is called cladistics.
Cladistics is a classification system based on common ancestry; it is a method of analysis that reconstructs phylogenies by inferring relationships based on shared characters

7. A cladogram is a branching, treelike diagram in which the endpoints of the branches represent specific species of organisms.

8. A node is the intersection of two branches.
A node represents the most recent common ancestor.

9. A clade is a group of organisms that share certain traits derived from a common ancestor.
A group that has none of the characters is known as an out-group.

10. FYI: The taxa group (organism) that has ALL the characters will be at the top of the cladogram and the taxa group with the least characters will be at the bottom of the cladogram. Remember, the most distantly related organism is called an out-group.

11. Two different ways of representing the
same pattern of evolutionary histories:
Cladogram
Phylogenetic Tree

12. Cladogram: What organism is most closely related to the bird?
What organisms have the derived character of hair?
What ancestral character is common to ALL the organisms?
Which organisms have amniotic eggs?
Which organisms lack a bony skeleton?
crocodile
Primates, rodents, rabbits
vertebrae
Primates, rodents, rabbits,
crocodiles, birds
Sharks

13. Phylogenetic Tree A node is the intersection of two branches.
A node represents the most recent common ancestor.

14. Phylogenetic Tree: 1. What organism is most closely related to the
minke whale?
a. cow
b. camel
c. humpback whale
2. What organisms is least
b. sheep 3 4 1 3 4 1