Lec 23: Evolution of Complexity Flashcards
How are complex traits evolved?
Initially a mutation starts of simple but is still adaptative, then some species face improvements which add greater complexity over time
What did greater complexity lead to?
Division of labor, like mitochondria being engulfed.
What type of selection is usually stronger?
‘Individual selection’ is stronger than ‘group’ selection. Natural selection will not favor the traits that reduce fitness of an individual.
When is cooperation adaptive?
- High relatedness: Genes that lead to helping relatives spread via natural selection
- Reciprocal Altruism: Species helping one another
- Cooperation sometimes breaksdown, ie selection for cheaters
Why do the sterile workers in honeybees selected by natural selection though they are sterile
They share many genes with the queen, hence there is an indirect selection
What is the target of selection?
Genes, as they are the unit of inheritance.
How do genomes stay co-coperative?
1, Mitosis and miosis: Equal amount of alleles are represented in daughter cells, they don’t compete.
- Development and multicellurity: Start with a single cell, prevent initial competition among cell lineages
- Uniparental Inheritance: chloroplasts and mitochondria replicate asexually. Prevents competition within cells of different organelle.
What is meiotic drive?
it occurs when an allele can bias its own transmission.
it is a case where ‘a’ frequency spread to higher frequency, even if it is not favoured
What are the ways cooperative alleles are achieved?
- Fair meiosis
- When cheating alleles spread, strong selection on rest of the genome for suppression of cheating
What is another way to cheat fair meiosos apart form meiotic drive?
Over-replication: Transposable elements (self-replicating elements of DNA) make copies of themselves excessively
How do the transposable elements not explode?
Alleles arising elsewhere silence the TE’s. Epigentitic reglation, pi-RNA was a mechanism of silencing the TE’s.
Transposition-selection balance: NATURAL SELECTION will play against this increase in mutation. The balance between elimination and creation determines how many copies are there.
How is mitochondria cooperative within us?
Mitochonria comes as uniparental. Hence this reduces the amount of diversity in the cells.
What is the problem of mitochondria spreading through uniparental?
The biparental nuclear genome is inherited, while only maternal inheritance is given.
Mitochondrial mutations that enhance female fitness is enhanced even if it is the severe cost to male fitness.
How do collection of cells stay cooperative?
- Starting from a single cell, reduces competition among individuals
- Separation of germline with a limited number of cell divisions inhibits transmission of selfish cell lineages
- Tumor suppressors, other features inhibit unregulated cell division.
