15. Evidence For Relationships Between Organisms

Question 0

How will the DNA of the new species become different from the original species it evolved from?

Answer 0

Due to mutations, the sequences of nucleotide bases in the DNA of the new species will change.

Question 1

When one species gives rise to another species during evolution, the DNA of the new species…

Answer 1

Will initially be very similar to that of the species that gave rise to it.

Question 2

What would we expect to observe as a result of the DNA of any new species changing?

Answer 2

We would expect species that are more closely related to show more similarity in their DNA base sequences than species that are more distantly related.

Question 3

Name one technique to determine similarities between the DNA of different organisms.

Answer 3

DNA hybridisation.

Question 4

What happens when DNA is heated?

Answer 4

It’s double strand separates into it’s two complementary single strands.

Question 5

What happens when you cool two separated strands of DNA which are complementary to each other?

Answer 5

They reform the original double strand.

Question 6

Describe the process of DNA hybridisation.

Answer 6

• DNA from two species is extracted, purified and cut into short pieces.
• The DNA from one of the species is labelled with a radioactive/fluorescent marker.
• The DNA of both species are mixed together and heated so the strands separate.
• the mixture is cooled to allow the strands to combine with other strands that have a complementary base sequence.
• hybridisation occurs
• the temperature is increased in stages, at each stage the degree to which the two strands are still linked together is measured.
• If two species are closely related they will share many complementary nucleotide bases and hence more hydrogen bonds linking them together in the hybrid strand.
• therefore, the higher the temperature at which the hybrid strand splits, the more closely the two species are related.

Question 7

Explain DNA hybridisation.

Answer 7

Some of the double strands that form will be made up of one strand from each species. This is called hybridisation.

Question 8

What are the new strands which have been put through hybridisation called?

Answer 8

Hybrid strands.

Question 9

How can hybrid strands be identified?

Answer 9

These can be identified because they are 50 per cent labelled.

Question 10

What are the two groups which plants are put into?

Answer 10

Monocotyledons - (single seed leaf, thin, narrow leaves)

Dicotyledons - (two seed leaves, broad leaves)

Question 11

Base sequences can be…

Answer 11

Compared using computer analysis and phylogenetic tree diagrams. E.g plants at kew.

Question 12

The sequence of amino acids in proteins is determined by DNA. The degree of similarity in the amino acid sequence of the same protein in two species will therefore reflect how…

Answer 12

Closely related the two species are.

Question 13

The amino acid sequences of two different species can be…

Answer 13

Compared to see how closely related two or more species are.

Question 14

How can proteins of different species be compared?

Answer 14

Using immunological techniques.

Question 15

What is the principle behind comparing proteins using immunological techniques?

Answer 15

Antibodies of one species will respond to specific antigens on proteins such a albumin in the blood serum of another.

Question 16

How is immunological protein comparison carried out?

Answer 16

-Serum albumin from species A is injected into species B
-Species B produces antibodies specific to all the antigen sites on the albumin from species A
-Serum is extracted from species B; this serum contains antibodies specific to the antigens on the albumin from species A.
- serum from B is mixed with Serum from C
- The antibodies respond to their corresponding antigens on the albumin in the serum of species C.
The response is the formation of a precipitate.

• A and C are being compared here. The role of B is to form antibodies for the serum of A which can combine with antigens in C.
• the greater the number of similar antigens, the more precipitate is formed and the more closely the species are related.

Question 17

Why is reproduction important to all organisms?

Answer 17

It is the means by which a species can survive over time.

Question 18

Each individual tries to ensure that…

Answer 18

Their DNA is passed on through the reproductive process, to the next generation.

Question 19

Courtship behaviour helps to achieve successful mating because:

Answer 19

Individuals can:

Recognise members of their own species to produce fertile offspring.

Identify a mate that is capable of breeding, both partners need to be sexually mature, fertile and receptive to mating.

Form a pair bond that will lead to successful mating and raising of offspring.

Synchronise mating so that it is successful.

Question 20

Why is courtship behaviour used by males?

Answer 20

To determine whether the female is at the receptive stage of her sexual cycle.

Question 21

When a male courts a female and she responds and gives the male a sign and the process repeats what is this called?

Answer 21

Stimulus-response chain.

Question 22

The longer the courtship sequence continues….

Answer 22

The more likely it is that mating will result.