Organism Relationships

Question 1

Genetic comparisons using DNA and proteins

Answer 1

Comparison of DNA base sequences- DNA hybridisation
Use of DNA base sequencing in classifying plants
Compare amino acid sequences in proteins
Immunological protein comparison

Question 2

Comparing DNA base sequences

Answer 2

Mutations change DNA base sequences. Over time more differences occur, so species more closely related show more similarity in their base sequences that distantly related species.

Question 3

DNA hybridisation

Answer 3

DNA from two species is extracted, purified, cut into short pieces.
One is labelled with a radioactive/fluorescent marker then mixed with the other.
It is then heated to separate the strands
It cools, allowing the strands to combine with other complementary bases
Hybrid strands are separated, and temperature is gradually increased.
The more different, the fewer hydrogen bonds and therefore the lower temperature required, and vice versa.

Question 4

Original plant classification

Answer 4

Monocotyledons have a single seed leaf, usually thin, narrow leaves
Dicotyledons have two seed leaves, usually broad leaves

Question 5

Plant classification by base sequencing

Answer 5

Used 565 species which represented each family of flowering plants known.
The DNA sequence of three genes were found in all of them.
They were compared using computer analysis
A phylogenetic tree was devised to show how species evolve into natural groups.

Question 6

Comparing amino acid sequences in proteins

Answer 6

This is determined by DNA. A protein has different amino acid sequences in different species, but those which are most similar show the species to be more similar.

Question 7

Immunological protein comparison

Answer 7

Two species share a common protein, but with different amino acid sequencing. Inject protein from A into B, which will produce antibodies against it. Repeat with B to C, and compare the precipitate formation.

Question 8

Reasons for courtship behaviour

Answer 8

Recognise members of their own species
Identify a mate capable of breeding
Form a pair bond
Synchronise mating

Question 9

Stimulus response chain

Answer 9

A male carries out an action which stimulates the female to respond with an action, causing another action from the male.

Question 10

Courtship sequence length

Answer 10

The longer the sequence, the more likely mating will result.