Methods for Determining Phylogenetic Relationships

REVIEW: Similarities and differences in DNA base sequences or amino acid sequences can be compared to determine evolutionary relationships. TODAY: Comparison of DNA sequences has led to new information about plants. DNA can also be compared through hybridisation.

Plant Classification Upon germination, the cotyledon may become the embryonic first leaves of a seedling. Species with one cotyledon are called monocotyledonous ("monocots"). Plants with two embryonic leaves are termed dicotyledonous ("dicots").

Flowering plants are classified into two groups: Monocotyledonous plants 1 cotyledon strap like leaves parallel veins flower parts divisible by 3 example: kaffir lily

Flowering plants are classified into two groups: Dicotyledonous plants 2 cotyledons broad leaves branching veins flower parts divisible by 4 or 5

Comparing monocotyledons and dicotyledons: Feature monocotyledon dicotyledon Number of cotyledons 1 2 Leaf shape strap like broad Vein pattern parallel branching Flower parts divisible by: 3 4 or 5 Example Kaffir lily Hibiscus

Which plant is a monocotyledon and which is a dicotyledon? B

Which plant is a monocotyledon and which is a dicotyledon?

BUT… This assumes that all plants with similar structures share a common ancestry. From animals, we know this might not be true…

Types of classification Artificial classification: Divides organisms by physical characteristics, such as size or number of legs. Describes by the same function, not the same evolutionary origin. What are the problems with this?

So, DNA sequences were analysed… Read the article and answer these questions: How were plants originally classified? How would these plants have been grouped originally? 3. Why is it important to understand about the evolution of plants?

DNA Comparisons Base sequences of particular genes are compared. In plants, this was genes for proteins involved in photosynthesis and other essential (and common!) functions. What genes might be analysed in animals?

DNA Hybridisation Closely related species have similar DNA base sequences. DNA strands can be separated by exposure to high temperatures.

DNA Hybridisation Mixing single stranded DNA from different species will allow hybrid DNA to form. The higher the temperature needed to separate the hybrid DNA, the more complementary bases were joined and the more closely related the species.

DNA Hybridisation

Comparing Proteins

Comparing Proteins

Comparing Proteins Most closely related: Donkey/human Cat/human Cat/dog Dog/human Duck/pigeon Then: Cat/donkey Dog/donkey Mammals/birds

Let’s draw an evolutionary tree Now try the cytochrome C question.

What’s left?

What’s left?

Easter Holidays Get your Unit 2 booklet up to date Catch up on lessons you’ve missed Identify topics you need help with Do some (more) revision: Notes Cards Test yourself Past papers etc.