Genes Evo & Dev L5 Notes

Question 1

• What is Fitness?

Answer 1

 The relative probability of survival & reproduction of a given genotype.

Question 2

• Who are ‘The Fit’?

Answer 2

 Varies according to environmental conditions
 Varies depending on number of copies of allele
 Possession of alleles enabling survival & reproduction.

Question 3

Describe Sickle Cell disease.

Answer 3

 Abnormal, sickled (sickle-shaped strands) & sticky red blood cells.
 Homozygotes
 Variety of problems Eg. Anaemia
 Advantageous in malarial zones -> Heterozygotes.
Heterozygotes less likely to get malaria

Question 4

• What is selected? (Units) & Describe the argument

Answer 4

 Unit of selection debated
 Gene
Self-replicating -> occasional errors -> influence survival/extinction.
 No specific unit
Units at various levels -> gene, individual, community -> all influencing gene of natural selection.
->Species -> not selected -> individuals within populations are.

Question 5

Argue why the gene is the unit of natural selection.

Answer 5

 Evolution -> change in allele frequencies
Possibility of evolution -> Phenotypes at least partly determined by genes
->Phenotype & genotype not necessarily directly linked
Genes can be linked together
->Incr. frequency of deleterious gene -> ‘Hitch-hiking’ -> physically close to
selected gene.
 Operates on individuals -> express phenotypes
Interact & transmit genes in different ways.

Question 6

What characteristics must the gene have if it is the unit of natural selection?

Answer 6

Self-replicating -> occasional errors -> influence survival/extinction.

Question 7

 Distinguish natural selection for vs. natural selection of something

Answer 7

Red blood not selected for -> haemoglobin selected for -> by chance red -> red blood cells.

Question 8

• Where does fitness lie?

Answer 8

 Some characteristics -> maladaptive -> reduce
fitness
-> Mainly sexual selection
 > Generally female choice
 Advantageous characteristics -> underlying direct/indirect correlation -> specific gene.
 Some characteristics -> maladaptive -> reduce fitness

Question 9

Why are social insects/ altruism not illustrated in the theory of evolution by natural selection?
Give an example of a mammal which exhibits similar behaviour.

Answer 9

• Evolution-> social systems/altruism -> not illustrated in theory of evolution of natural selection Eg. Social insects
Most social insects -> sterile
>Only queen reproduces
Naked mole rats also share this trait -> work like ant colony

Question 10

What is altruism?

Answer 10

• Altruism
 Behaviour of an animal
Benefits another at it’s own expense.

Question 11

What is inclusive fitness?

Answer 11

• Inclusive fitness
 Direct & indirect fitness
(fitness of related offspring) -> ‘kin selection’

Question 12

Outline Hamilton’s Rule

Answer 12

• Hamilton’s Rule
 Natural selection of genes -> lead -> social selection
 Genes shared between possessor & recipient.
 Altruism has cost (c) -> performer
 Altruism has benefit (b) -> recipient
 Depends on degree of relatedness (r)
 Altruism
 rb > c
 Likely when r is high -> social insects.
 Gene for altruism -> Highly unlikely
Altruistic effects -> produced by response to individuals with similar genotype
 Origins -> highly related -> small groups
Possible explanation of widespread human altruism

Question 13

Give examples of hymenoptera

Answer 13

 Wasps, ants & bees

Question 14

What is Haplodiploidy of a species represented by?

Answer 14

 Diploid females & haploid males

Question 15

Describe a theory as to how social systems evolved?

Answer 15

Haplodiploidy of Hymenoptera: Hymenoptera -> more closely related
-> sister -> than to -> own offspring
 Genes more likely -> passed to next generation -> female rears sister’s offspring rather than having own.
 Relatedness may be lower -> queen -> mates -> multiple males
Ancestral form mated -> single male
->Explains evolution of system

Question 16

Describe Hamilton’s rule using haplodiploidy of hymenoptera as an example.

Answer 16

 Hymenoptera -> more closely related
-> sister -> than to -> own offspring
 Genes more likely -> passed to next generation -> rear sister rather than having own offspring.
 Relatedness may be lower -> queen -> mates -> multiple males
Ancestral form mated -> single male
->Explains evolution of system
 Close relatedness -> not precondition/determining factor
Ecology -> shapes evolution of species.
 Many hymenoptera -> not eusocial
Solitary bees, sawflies, parasitoid wasps etc.
Eg. Termites -> XY sex determination -> based on close relatedness of individuals.

Question 17

Is close-relatedness a pre-determining factor of Hamilton’s rule? Explain why.

Answer 17

 Close relatedness -> not precondition/determining factor

Ecology -> shapes evolution of species.

Question 18

Outline two views in the inclusive fitness debate.

Answer 18

 Hamilton’s theory -> kin selection theory

 Wilson’s theory -> kin selection doesn’t explain altruism

Question 19

Describe Hamilton’s theory in terms of the inclusive fitness debate.

Answer 19

• Inclusive Fitness Debate:
 Hamilton’s theory -> kin selection theory
- Organisms can pass genes to future generations indirectly
–> rearing kin’s offspring
- Kin shares half of individuals genes -> half as good as raising own offspring
-> not self-sacrifice

Question 20

Describe Wilson’s view on the inclusive debate.

Answer 20

 Wilson’s theory -> kin selection doesn’t explain altruism

• Species -> many common genes -> don’t illustrate altruism
• Species -> little genetic similarities -> demonstrate altruism.

Question 21

What is Wilson’s alternative theory to Hamilton’s in the inclusive fitness debate?

Answer 21

• His theory:
  Under certain conditions, groups of mutualistic organisms can out-compete those that aren’t mutualistic
  >Ensures genes (incl. ones coding for mutualistic behaviour) -> passed to subsequent generations.
  Kinship & relatedness aren’t essential for development of altruistic behaviour
  >Altruism -> advantageous in groups
  -> Rearing kin’s offspring -> chance result of group membership; not cause.

Question 22

Describe how species are classified

Answer 22

• Species classified based on shared anatomical & phylogenetic characteristics
 Anatomical sometimes ambiguous -> Both cows & lizards have backbone but not closely related.
 Molecular sequences (DNA, RNA, protein) -> compared for study of relationships -> more objective & less ambiguous.

Question 23

Describe how evolutionary relationships can be determined between related organisms. Give examples.

Answer 23

• Related organisms -> common ancestor -> common ancestral DNA sequence.
 As evolution occurs over time -> DNA sequence accumulates mutations.
Can be used to study evolutionary relationships.
Eg. SNPs & Indels
- SNP -> Single Nucleotide Polymorphism -> mutation
-> one nucleotide base -> replaced with another
- Indels -> mutation -> insertion/deletion of one or more nucleotide base.

Question 24

What is a SNP?

Answer 24

• SNP -> Single Nucleotide Polymorphism -> mutation

- > one nucleotide base -> replaced with another

Question 25

What is an indel?

Answer 25

• Indels -> mutation -> insertion/deletion of one or more nucleotide base.

Question 26

How can we tell if species are more closely/distantly related?

Answer 26

• Species -> more distantly related
 Incr. number -> differences in DNA sequences -> mutations
 Incr. number -> different anatomical features.

Question 27

What are the requirements for comparison of DNA sequences?

Answer 27

• Requirements for comparison of DNA Sequences:
 Must be homologous -> evolutionarily related.
 Aligned -> related parts of sequence lined beside each other -> enabling comparison.
 Multiple sequences can be aligned
 Maximise number of matching nucleotide sequences on both strands
Computers
Adjust relative positions &/ add gaps
Each line -> one DNA sequence
 Each column -> position in alignment
 Asterisk -> all letters in column match.

((Eg. ACAGACGA & ACATACAGA
-> ACAGAC-GA & ACATACAGA. -> *** ** **

Eg. ACAGACGA & ACATACAGA & ACTACGA
ACAGAC-GA & ACATACAGA & AC-TAC-GA -> ** ** **))

Question 28

How is an SNP mutation identified during DNA sequence comparison?

Answer 28

• SNP alignment -> letters in column don’t match

Question 29

How is an Indel mutation identified during DNA comparison?

Answer 29

• Indel alignment -> gap/dash (-) in alignment.

Question 30

Describe how a phylogenetic tree can be built form DNA sequences.

Answer 30

• Calculate distance value from specific sequence.
  (# of changes between both sequences)/(length of each sequence
• End of each branch -> represents species/sequence; or a group of related species/sequences.
• Place -> two branches split apart -> branch point.
  Represents most recent common ancestor of all species on those branches
  May be made obvious by small node/point on line.
• Single branch -> all branches originate -> Root
  Node closest to root ->most recent common ancestor of all organisms in tree
• Unrooted tree -> relative relationships -> group of species
• -> no illustration -> common ancestor.

Question 31

How is the distance value for a phylogenetic tree calculated?

Answer 31

(# of changes between both sequences)/(length of each sequence)

Eg. 1. GCAGGGATACT
2. GCTGGCATTCT -> distance -> 3/11 -> 0.27

Question 32

How can phylogenetic trees using DNA sequences be used to cross-check other forms of phylogenetic tree?

Answer 32

• Phylogenetic tress -> DNA sequences -> v. similar -> trees using other evidence -> Eg.Comparitive anatomy
  Predictive of shared traits
  Eliminates uncertainties -> other trees.

Question 33

Who came up with theory ->

survival of the fittest?

Answer 33

Herbert Spenser