Assign Yourself: IA2 Review (both sides)

• Take out your science journals—we are going to grade them.

Announcement:

• 1st dissection taking place THIS FRIDAY

Take out your science journal! We are going to grade it!

Common Ancestors

What kinds of traits can be inherited?• Only inheritable traits (genetic traits) can be passed

from parents to offspring. Examples: eye color, height• Acquired traits (anything not controlled by genes),

CANNOT be passed on.Examples: tattoos, dyed hair, injuries

What happens when 2 populations of the same species are living in different environments?

• Over time, natural selection causes populations to change so they are better adapted to (better at surviving in) their environments.

• If 2 populations are living in different environments, they might change so that each one is better adapted to its own environment.

Example: Birds living on the Galapagos islands

Processing Piece:• Look at the birds in this picture. What variation

(different traits) do you see?• Why might they have this variation?

Processing Piece:• In a population of birds, some birds had thin beaks

and some birds had large, thick beaks. Thin beaks were better for grabbing insects, and thick beaks were better for cracking seeds. The birds migrated to two island habitats. One island had lots of insects, and the other had lots of seeds. What do you predict would happen to the populations on the different islands?

What are the Galapagos finches?• Different species of finches,

each living on one of the Galapagos islands

• Each has its own type of beak

• Each beak is good for eating the food source most common on that island.

• The finches all share a common ancestor.

What is a common ancestor?An individual or species that was alive in the past, that 2 or more different groups of organisms alive today are descended from.

Processing Piece:• Look at the birds in the picture below. Circle the one

that you think is the common ancestor.

What is a phylogenetic tree?Like a family tree that shows the relationships between different species or populations.

Processing Piece:• Circle the most recent common ancestor of…

Processing Piece:• Based on this tree, which is most closely related to

birds: crocodiles or turtles?

Processing Piece:• Based on this tree, which is most closely related to

lizards: crocodiles or mammals?

What are 2 ways we can tell that 2 groups probably share a recent common ancestor?

1) Biogeography clues – when species that are very similar live near each other, but are separated, it’s likely that they came from a common ancestor.Example: birds on the Galapagos islands

What are 2 ways we can tell that 2 groups probably share a common ancestor?

2) Similar nucleotide sequences – when the DNA of two different species is similar, it’s likely that they share a common ancestor.

Nucleotide = bases (A, T, G, and C)Sequence = the order that they’re in

Processing Piece:• Write “Evidence for Common Ancestry.” • Underneath it write “2. Nucleotide Sequences” and

draw a picture to help yourself remember the definition.

Example: AAT TAG AAT GCAAAT TAC AAT CCA

CCA GGT CAG TTA

Share a common ancestor

Exit Ticket1. What is the difference between an

inheritable trait and an acquired trait?2. What is a common ancestor?3. Name 2 types of evidence that indicate

organisms might share a common ancestor?