Evolution

Question 1

Define evolution(3)

Answer 1

Accumulated, heritable changes within a population, over generations, giving rise to new species

• New species arise from earlier species
• Evolution is an observable fact. The process by which it has most likely occurred, natural selection, is a theory. Theory because we cannot observe it.

Question 2

Why are mutations important?(3)

Answer 2

· Mutation rates can act as molecular clocks

· Mistakes/ mutations accumulate over time

· Species that share a recent common ancestor with fewer differences than species that are more distantly related

Question 3

How are phylogenetic trees made?(2)

Answer 3

· Molecular differences can be used to construct phylogenetic trees.

· Myoglobin evolution- a molecular phylogenetic tree.

Question 4

What is the difference between classification and taxonomy?

Answer 4

• Taxonomy- naming groups of organisms
• Classification- arranging taxa into an ordered hierarchical system

Question 5

What is the difference between genetic flow and drift?

Answer 5

• Genetic drift- Variation in relative frequency of different genotypes in small populations
• Gene flow- transfer of alleles from one population to another

Question 6

Describe the experimented conducted to show evolution using e.coli(4)

Answer 6

“• 12 colonies of E. coli all derived from a single clone.

The bacteria growing in citrate in the presence of oxygen. In low amounts of glucose their preferred energy source. High citrate levels cannot be used in oxygen

• Everyday for 31 years, 10 % of each have been removed for subculture
• Freeze culture samples every 500 generations 75 days • Over 73000 generations have been observed • Differences between cultures have emerged over the years “

Question 7

What were the results of the e.coli experiment(3)

Answer 7

• One group developed ability to use citrate in oxygen evolved after about 30000 generations in one group
• E. coli can’t use citrate in oxygen because gene is turned off in oxygen
• Earlier generations from this same ancestral e. coli were repeatedly able to evolve the ability to use citrate at about the same time

Question 8

Describe citrate use in e.coli(7)

Answer 8

→The ability of bacteria to utilise citrate is controlled by its citrate gene, controlled by the citrate promoter.

→gene is normally turned off in the presence of oxygen.

→ It is next to the RNK promoter, which controls the RNK gene.
→This is turned on in the presence of oxygen.

→in cultures that were able to utilise citrate, the citrate gene and RNK promoter were duplicated right after each other.

→this doesn’t affect the existing citrate gene, but the duplicated citrate has an RNK promoter before it which means it is under the control of the RNK promoter.

→citrate gene now works in the presence of oxygen.

So E.coli can survive in citrate

Question 9

Describe the evidence of homology and analogy(3)

Answer 9

Humans have humerus, radius and the ulna and the metacarpals

That pattern is conserved through all tetrapods.

single element- stylopod, the paired element is zeugopod, autopods- hand digits.

In the horse- the radius and ulna have fused like the metacarpals have fused. “

Question 10

what does analogous mean in relation to evolution?(3)

Answer 10

→ two structures are analogous when they have no common ancestor

→ the similar structures are produced by selection to meet similar function (convergent evolution)

→ they have different developmental mechanisms but some molecular components may be the same. An example would be insect wings and bird wings.

Question 11

What are crystallins?(7)

Answer 11

crystallins are all proteins that have been adapted from their original function to be constituents of the optics of animal eyes • Alpha crystallins are related to HSPs- heat shock

• So have been recruited to a lens function
• Beta/gamma crystallins are homologous
• But many other different lens proteins exist in different species
• These tend to be enzymes/have enzymatic activity
• in addition to being soluble, stable, transparent & refractive

Question 12

what does homologous mean in relation to evolution?(2)

Answer 12

→two structures are homologous when they are derived from a common ancestral version.

→these structures are derived from a common ancestor so they form by a common mechanism. An example would be tetrapod limbs.

Question 13

Describe the difference between paralogues and orthologues and give examples with hox genes

Answer 13

• Two genes from same organism (by duplication) – paralogs- species (eg Mouse Hox a1, a2, a3, a4 etc are paralogues)

Two genes from different organisms (common ancestor) – orthologs eg the fruit fly Antennapedia gene is the orthologue of mouse Hox a6, b6, c6”

Question 14

What are hox genes?(4)

Answer 14

Hox genes control the body plan of organisms with each hox gene coding for a specific body part.

• Hox genes represent transcription factors
• Hox genes bind DNA in a sequence-specific fashion and regulate the expression of adjacent/nearby genes
• Confer positional identity along the Anterior-Posterior (cranio-caudal) axis

Question 15

Describe hox genes in Drosophilia(5)

Answer 15

• Segments in the larvae stage of the insect.

T2 and T3 is where antonpoedia gene is expressed- tells those segments to be thoraxic.

3. Mutation is not disruption of gene but to mis expressed in the head region and directs appendages to form legs.
4. there are 8 hox genes duplicated from an ancestral form.
5. • Different hox genes are expressed in head to tail pattern in the organism and are homologues of one another. “

Question 16

Describe hox gene evolution in humans(3)

Answer 16

“Ancestral hox gene emerged and it was duplicated and duplicate

2. In vertebrates the cluster has been duplicated and duplicated again so that there are 4 gene clusters ranging from numbers 1-13.
3. There have been losses of genes in the clusters but fundamentals has remained Genes toward the left is the head and genes toward the right is the tail end “

Question 17

What is the homeodomain?(4)

Answer 17

1. The DNA-binding part of Hox genes, the homeodomain, is used in other, related transcription factors
2. The general structure of a homeodomain can be described as Helix-Loop-Helix-Turn-Helix
3. HP is the homeodomain protein that characterises specifically as a hox gene
4. PAX gene share the homeodomain but is joined by the paired domain and modifies characteristics of the transcription

Question 18

Describe origins of life on earth(5)

Answer 18

• The RNA World hypothesis
• Early life is thought to have been based on self-replicating, self-catalyzing RNA molecules
• Catalytic RNAs (ribozymes) are present in organisms from bacteria to humans
• The RNA world evolved into a DNA genome/protein enzyme world •

DNA more stable than RNA, greater range/robustness of protein enzymes “

Question 19

How are things radioactively dated?(2)

Answer 19

There are some commonly used isotopes. The radioactive isotopes decay to give a characteristic daughter isotope

To date a sample of rock- the radioactive material at the beginning is needed and then measure the current material

Question 20

How do igeneous rocks enable radioactive dating?(3)

Answer 20

• In igneous rocks, once the rock is formed it forms an impervious barrier.

As the parent atom decay there is an exponential increase of the same proportion of its corresponding daughter atom.

When the molten rock forms it is a closed system so the relative ratio of the parent and daughter atoms can be measured.

Question 21

What are the requirements of radiometric dating?(6)

Answer 21

• The rate of radioactive decay is constant
• Not affected by temperature, pressure, chemicals, electrical or magnetic fields
• Parent and daughter nuclides cannot leave or enter material after it is formed
• No intrusion of other, later rock
• No contamination
• Fossils are dated by looking at the layers of previously molten rock on either side of the band

Question 22

Describe eukaryotic cell evolution(3)

Answer 22

Prokaryotic host has engulfed with another kind of bacteria eg aerobic bacterium – mitochondria and cyanobacterium- chloroplast

• Eukaryotic cells arose through endosymbiosis or predation of a-protobacteria and archaeal host
• Endosymbiosis generated organelles, and nucleus

Question 23

What evidence is there to support endosymbiosis involving mitochondria and Rickettsioses?(4)

Answer 23

” • Mitochondria have their own circular genome which replicates independently of nuclear linear DNA

• New mitochondria are produced by fission of existing mitochondria
• All mitochondrial genomes share similarity with the Typhus bacterium Rickettsia prowazekii
• Rickettsioses are obligate, intracellular parasites or symbionts of eukaryotes- they have to live as intracellular parasites. Cant survive outside of the environment

Question 24

What do chloroplasts resemble?

Answer 24

” • cyanobacterial DNA “

Question 25

What are the four basic processes of multicellularity?

Answer 25

" • Spatial organization * Change in form * Growth * Differentiation- to use basic building blocks of different genes

Question 26

What type of rocks do fossils form in and what does this mean for the dating of the fossil?

Answer 26

• Fossils usually form in sedimentary rock- so the rock wont be the same age as the fossil

Question 27

What are the three main components of the eye?

Answer 27

"Photoreceptor, lens, aperture"

Question 28

What is the difference between human photoreceptors and insects photoreceptors?

Answer 28

Humans Photoreceptors have cilia on them derived from neural tissue. Some insects have microvilli instead of cilia

Question 29

Are crystallin in different taxa the same and why?

Answer 29

"• Crystallin in different taxa are not related. Different taxa use diff soluble proteins- usually proteins with enzymatic parts.

Question 30

What are the differences between eyes of different eukaryotic organisms?

Answer 30

ALL eukaryotes use a homologous family of proteins, opsins, to detect light * Opsins are G-protein coupled receptors that convert light to nerve impulses * Eukaryotic opsins share sequence homology and have diverged to detect different wavelengths of light "

Question 31

What is the difference betwen the opsins prokaryotes use?

Answer 31

Prokaryotes also have GPCR opsins, but with a different molecular origin – convergent evolution

Question 32

What is the role of PAX6 gene?

Answer 32

* Pax6 involved in eye development throughout animal kingdom- is the use of pax 6 a result of homologous or convergence * But Pax 6 is not a master gene because other genes can induce ectopic eyes. Animals that have pax 6 do not have eyes • Pax 6 is present in diff region of the embryo and is required for the function of the tissue. Pax 6 is used in other genes * More likely that it organises a gene network required for eye formation

Question 33

Summarise the experiment on mouse and Drosophilia eyes(3)

Answer 33

* eyeless is orthologous to Pax6 in humans (aniridia) and mutations in mouse (smalleye) * Ectopic expression of eyeless in Drosophila embryo where it is not normally expressed \> Gives rise to ectopic eyes * Mouse Pax6 gene functions in drosophila cause eyes to form where it is being expressed

Question 34

Why does the cavefish eyes degenerate?(2)

Answer 34

* The lens is essential for the development of other parts of the eye * Cavefish lens is smaller and undergoes apoptosis "

Question 35

What is the evidence for human evolution?(5)

Answer 35

" • Mitochondria are maternally inherited * The mitochondrial genome replicates independently of the nuclear genome and does not undergo recombination * Similarly, the male Y chromosome does not have a homologous female chromosome to recombine with. Random mutations give rise to changes * Changes in sequence of mtDNA and the Y chromosome are due to random mutations over time * Analysis of mtDNA and Y chromosome sequence shows maternal and paternal origin, respectively

Question 36

Describe the evidence for modern human evolution involving hypoxia(4)

Answer 36

* Different populations have adapted to hypoxia in different ways. This is an example of convergent human evolution * Populations living in the mountains have low oxygen levels- found ways of adapting – producing more haemoglobin so can carry more oxygen in their blood * Those in China -Adapted by regulating HF1, transcription factor turned on in low oxygen * Those in south America by making more haemoglobin and by mutation in HIF12

Question 37

What are the shared characteristics between the three domains?

Answer 37

Question 38

What prokaryote does mitochondria have in common with regarding DNA?

Answer 38

Typhus bacteria

Question 39

What prokaryote DNA share similarites with chloroplasts?

Answer 39

Cyanobacteria DNA

Question 40

why did RNA world evolve into DNA?

Answer 40

→DNA is more stable than RNA → there is a greater range of protein enzymes and they are more robust

Question 41

what does Pax 6 have to do with the development of the eye?(3)

Answer 41

→Being eyeless is orthologous to Pax6 in humans and mice. →The ectopic (differently placed) expression of the eyeless gene in drosophilia (fruit flies) leads to ectopic eyes. →Pax6 is involved in eye development throughout the animal kingdom

Question 42

how many Hox genes do vertebrates have and how have they arisen?

Answer 42

→Vertebrates have four Hox gene clusters →which have arisen from two duplication events of an ancestral chromosome.