Download Body Structures

Warm-Up 5/18/2010
• Why are transitional fossils important evidence
for evolution?
• Give two examples of transitional fossils
-Take out 17.1 + 454-455 Notes to be stamped
Evidence for Evolution
Body Structures, Embryos,
DNA/RNA Comparisons
Homologous Structures
• Structures with different mature forms but come
from same embryonic tissues
• Best seen in animals with backbones
• Ex: humans, cats, whales, and bats all have same
basic bones in their limbs
• Evidence that all four-limbed animals with
backbones descended (with adaptations) from
common ancestor
Homologous Structures
Vestigial Structures
• Some organisms have
traces of homologous
structures that they
no longer use
• Ex: human tailbone,
human appendix,
snake leg buds
Comparative Embryology
Embryos of diverse organisms look very similar!
Comparative Embryology
• Shows that same groups of embryonic cells
develop in same order and in same patterns to
produce organs, etc.
• Groups of cells produce homologous structures
Snapping Turtle Embryo
Cat Embryo
DNA/RNA Comparisons
• Genetic similarities between organisms help
scientists determine correct phylogenetic trees
▫ How closely related organisms are
▫ Who evolved from who, even when physical
similarities aren’t obvious
Afr. Vulture
Am. Vulture
Stork
Types of Evidence from DNA/RNA
• Highly related organisms
share a high percentage of
DNA in common
▫ Humans and chimps share
96% of DNA in common
▫ About 40 million differences in
3 billion nucleotides
▫ Only 2,000 of these differences
code for something
(Emory University, 2005)
Types of Evidence from DNA/RNA
• Seemingly unrelated organisms share genes that
code for the same proteins
▫ Humans and yeast both have the gene that
produces the protein myosin
▫ Myosin is used in human muscle tissue
▫ Myosin in yeast helps organelles move
“Molecular Clocks”
• The number of mutations found in DNA can
help us estimate the length of time between the
evolution of two organisms
▫ Mutations accumulate at a constant rate
▫ The more differences between two organisms, the
longer apart they evolved from each other
Human/Chimp Chromosome Activity
• Read Background and Answer a, b, c (p. 1)
• Do Chromosome Analysis #1-9 (p. 1, 2)
• Comparison of Human/Chimp Chromosomes:
Do 1, 2 and Answer 3 a-g