Evidence for Relationships Between Organisms

Question 1

State how comparisons of biological molecules in two species can be used to find if the two species are closely related

Answer 1

-Compare DNA/sequence of bases/nucleotides
-DNA hybridisation - Separate DNA strands/break hydrogen bonds
- Mix DNA/stands (of different species)
- Temperature required to separate (hybrid) strands
indicates relationship
-Compare same/named protein - primary structure
-Immunological evidence - inject protein/serum into animal
- (obtain antibodies/serum
- Add protein/serum from other species
- Amount of precipitate indicates relationship

Question 2

Explain why comparisons between base sequence of gene provides more info than comparing amino acid sequence

Answer 2

• Triplet code/more bases than amino acids/longer base sequence than amino acid sequence
• Introns/non-coding DNA
• Same amino acid may be coded for/ DNA code is degenerate

Question 3

Why is it important to use samples of hybrid DNA from the same gene during DNA hybridisation?

Answer 3

• Base sequence will be similar/some bases in common

- These bases will bind together/hydrogen bonds/complementary base pairs

Question 4

What causes DNA to separate at higher temperatures?

Answer 4

• Relationship is closer/more complementary bases/more base pairs
• More hydrogen bonds
• More heat energy needed (to separate bonds)

Question 5

How should biologists should carry out breeding experiments?

Answer 5

• Cross animals from two sites/watch courtship
• Breed young together/observe maiting
• Improve quality of results (isolation beforehand/large sample size)
• If same species the animals would breed, producing fertile young/courtship is species specific

Question 6

Describe how antibodies against human haemoglobin can be used to compare evolutionary relationships between different species

Answer 6

• Antibody and hhaemoglobin/blood (of different species) mixes
• Precipitate forms
• Amount of precipitate shows relationship/similarity (in protein/DNA)

Question 7

Name ways in which courtship behaviour increases probability of successful mating

Answer 7

• Recognition of same species
• Stimulates release of gametes
• Recognition of opposite gender
• Indication of sexual maturity/fertility
• Form a pair bond