Evidence for relationships between organisms. (UNIT 2)

Question 1

What changes when organisms evolve and why does this cause a change?

Answer 1

Changes in DNA.

DNA determines the proteins of an organism including enzymes and proteins determine the features of an organism.

Question 2

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

Answer 2

Very similar to that of the species that gave rise to it.

Question 3

When new species are created, why does there DNA gradually become more different from the species they arose from?

Answer 3

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

Question 4

You would expect species who are more closely related to show…

Answer 4

more similarities in their base sequences than species that are more distantly related.

Question 5

What property of the DNA double helix does DNA hybridisation rely on?

Answer 5

When DNA is heated, its double strand separates into its two complementary single strands.
When cooled, the complementary bases on each strand recombine with each other to reform the original 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 species is labelled by a radioactive or fluorescent marker to it. It is then mixed with unlabelled DNA from the other species.
• The mixture of both sets of DNA is heated to separate their strands.
• The mixture is cooled to allow the strands to combine with other strands that have a complementary sequence of bases.
• Some of the double strands that reform will be made up of one strand from each species. This is called hybridisation and the new strands are called hybrid strands. IDENTIFIED BECAUSE ARE 50% labelled.
• Strands separated out and the temperature is increased IN STAGES.
• AT each temp. stage the degree to which the new strands are still linked together is measured.
• If two species are closely related they will share many complementary nucleotide bases.
• Therefore be MORE HYDROGEN BONDS linking them together in the hybrid strand.
• The greater the number of hydrogen bonds, the stronger the strand will be.

Question 7

Describe the relationship between the strength of a hybrid strand and the temp. needed to split it into two strands.

Answer 7

The stronger the hybrid strand (more hydrogen bonds=complementary nucleotide bases), the higher the temperature needed to separate it into two separate strands.

Question 8

Describe the relationship between temperature needed to split a hybrid strand in two and how closely related a species are.

Answer 8

The higher the temp at which the hybrid strand splits (more hydrogen bonds), the more closely related two species are.

The lower the temp at which the hybrid strand splits , the more distantly the species are related.

Question 9

Until recently, how were plants classified?

Answer 9

Based on the appearance of a plants physical features.

Question 10

How was a new classification for plants made up?

Answer 10

3 gene sequence found in ALL plants:
-565 species of plant that between them represented all the known families of flowering plants in the world.

• For each plant, the DNA base sequences of all three genes were determined.
• The sequences for each species were compared using computer analysis.
• A phylogenetic tree for the families of flowering plants was devised based upon the DNA sequences of the species used.

PHYLOGENETIC TREE SHOWED HOW SPECIES HAVE EVOLVED INTO NATURAL GROUPS

Question 11

What is the sequence of amino acids in proteins determined by?

Answer 11

DNA

Question 12

What does the degree of similarity in the amino acid sequence of the same protein in two species reflect?

Answer 12

How closely related the two species are.

Question 13

How are amino acid sequences compared?

Answer 13

Either by counting the number of similarities or the number of differences in each sequence.

Question 14

What is the principle behind immunological comparison?

Answer 14

The fact that antibodies of one species will respond to specific antigens on proteins in the blood serum of another.

Question 15

How is the process of immunological comparison carried out?

Answer 15

• Serum albumin (protein) 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 species B is mixed with serum from blood of a third species 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.
• The greater the number of similar antigens, the more precipitate is formed and the more closely related the species are.
• The fewer the number of similar antigens, the less precipitate is formed and the more distantly related the species are.

Question 16

What does courtship behaviour allow species to do? (4)

Answer 16

• Recognise member of their own species- to ensure mating only takes place between members of the same species. Only members of the same species can produce fertile offspring.
• Identify a mate that is capable of breeding- because 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 takes place when there is the maximum probability of the sperm and egg meeting.

Question 17

Why is courtship behaviour important?

Answer 17

Reproduction is important for the continuation of a species.
Need to ensure that their DNA is passed on to next gen.
Females of most species only produce an egg at certain times, important to ensure that mating is successful and offspring have max. chance of survival.

Question 18

What does courtship behaviour tell the male about the female?

Answer 18

Determines whether female is capable of breeding (Females of many species undergo a cycle of sexual activity during which they can conceive). Makes sure female is at this receptive stage.

If female responds with appropriate behavioural response, courtship continues, if she is not receptive, she exhibits a different pattern of behaviour and the male ceases to court her.

Question 19

How is the process of courtship often carried out? i.e. STIMULUS RESPONSE CHAIN

Answer 19

Animals use signals to communicate with a potential mate.
Typically a male carries out some action.
This action acts as a stimulus to the female, who responds with a specific action of her own.
her response acts as a stimulus to the male to carry out further action.
Same for all members of a species but differs for members of different species.

Question 20

How do animals tell during courtship if other animal is the same species and is ready to mate?

Answer 20

Species have different courtship behaviour.

Different signals for whether ready to mate or not.

Question 21

The longer the courtship sequence continues the more likely…

Answer 21

it is that mating will result.

Question 22

If at any point one of the pair fails to respond appropriately, then the courtship sequence…

Answer 22

ends.