Genes Evo & Dev L5 Notes Flashcards
• What is Fitness?
The relative probability of survival & reproduction of a given genotype.
• Who are ‘The Fit’?
Varies according to environmental conditions
Varies depending on number of copies of allele
Possession of alleles enabling survival & reproduction.
Describe Sickle Cell disease.
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
• What is selected? (Units) & Describe the argument
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.
Argue why the gene is the unit of natural selection.
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.
What characteristics must the gene have if it is the unit of natural selection?
Self-replicating -> occasional errors -> influence survival/extinction.
Distinguish natural selection for vs. natural selection of something
Red blood not selected for -> haemoglobin selected for -> by chance red -> red blood cells.
• Where does fitness lie?
Some characteristics -> maladaptive -> reduce
fitness
-> Mainly sexual selection
> Generally female choice
Advantageous characteristics -> underlying direct/indirect correlation -> specific gene.
Some characteristics -> maladaptive -> reduce fitness
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.
• 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
What is altruism?
• Altruism
Behaviour of an animal
Benefits another at it’s own expense.
What is inclusive fitness?
• Inclusive fitness
Direct & indirect fitness
(fitness of related offspring) -> ‘kin selection’
Outline Hamilton’s Rule
• 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
Give examples of hymenoptera
Wasps, ants & bees
What is Haplodiploidy of a species represented by?
Diploid females & haploid males
Describe a theory as to how social systems evolved?
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
Describe Hamilton’s rule using haplodiploidy of hymenoptera as an example.
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.
Is close-relatedness a pre-determining factor of Hamilton’s rule? Explain why.
Close relatedness -> not precondition/determining factor
Ecology -> shapes evolution of species.
Outline two views in the inclusive fitness debate.
Hamilton’s theory -> kin selection theory
Wilson’s theory -> kin selection doesn’t explain altruism
Describe Hamilton’s theory in terms of the inclusive fitness debate.
• 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
Describe Wilson’s view on the inclusive debate.
Wilson’s theory -> kin selection doesn’t explain altruism
- Species -> many common genes -> don’t illustrate altruism
- Species -> little genetic similarities -> demonstrate altruism.
What is Wilson’s alternative theory to Hamilton’s in the inclusive fitness debate?
- 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.
Describe how species are classified
• 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.
Describe how evolutionary relationships can be determined between related organisms. Give examples.
• 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.
What is a SNP?
- SNP -> Single Nucleotide Polymorphism -> mutation
- > one nucleotide base -> replaced with another
What is an indel?
- Indels -> mutation -> insertion/deletion of one or more nucleotide base.
How can we tell if species are more closely/distantly related?
• Species -> more distantly related
Incr. number -> differences in DNA sequences -> mutations
Incr. number -> different anatomical features.
What are the requirements for comparison of DNA sequences?
• 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 -> ** ** **))
How is an SNP mutation identified during DNA sequence comparison?
- SNP alignment -> letters in column don’t match
How is an Indel mutation identified during DNA comparison?
- Indel alignment -> gap/dash (-) in alignment.
Describe how a phylogenetic tree can be built form DNA sequences.
- 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.
How is the distance value for a phylogenetic tree calculated?
(# of changes between both sequences)/(length of each sequence)
Eg. 1. GCAGGGATACT
2. GCTGGCATTCT -> distance -> 3/11 -> 0.27
How can phylogenetic trees using DNA sequences be used to cross-check other forms of phylogenetic tree?
- Phylogenetic tress -> DNA sequences -> v. similar -> trees using other evidence -> Eg.Comparitive anatomy
Predictive of shared traits
Eliminates uncertainties -> other trees.
Who came up with theory ->
survival of the fittest?
Herbert Spenser
