Lecture 10 - Evolution of Sex Flashcards
Mitosis of bacteria vs eukaryotes
Bacteria
- > origins of replication move to opposite poles during fission
Eukaryotes
- > spindle forms ooutside nucleus (which is broken down), microtublues separate chromosomes
Different types of Asexual reproduction
*ALL ARE CLONAL - DOESN’T ENHANCE GEN. VARIANCE*
Early
- > fission
- > budding
More recent
- > fragmentation (organism spits i.e. starfish)
- > parthenogenesis (development of egg w/out fertilization)
Apomixis
produces a seed which is a clone of itself (i.e. dandelions)
Why did sex evolve from asexual to sexual reproduction
sexual reproduction allows for more genetic variation
recombination
occurs when two molecules of DNA exchange pieces of their genetic material with each other (crossing over)
Sexual vs Asexual reproduction
Asexual
- > greater reproductive output
- > no recombination but good in…
* stable environments
*speces with rapid generation times (increased mutation)
Sexual
- > reduced reproductive output
- > involves recombination
* generates new genotypes facilitating natural selection
* Allows for longer generation times
Isogamy vs Anisogamy vs Oogamy
*ALL TYPES OF SEXUAL REPRODUCTION*
Isogamy (quantity)
- > no greater investment in one or the other; cells are equal
Anisomy and Oogamy (quality)
- > produces fewer females, as they are heavily invested in because they need a quality egg
How do genetic changes occur in asexual reproduction/offspring
mutations
Diplontic
- > diploid dominates most of the live cycle, haploid confined to the gametes
Haplontic
haploid dominates most of life cycle, diploid confined to zygote
Haplodiplontic
- > alternation of generations
- > having diploid and haploid stages of life
Advantages of being haplontic
- > advantageous when individuals are fully adapted to environment
- > fewer chromosomes = fewer mutations
- > mutations immediately expressed and exposed to selection
*deleterious = removed from pop
* beneficial = spread through pop
Advantages of being diplontic
- > advantageous in unstable environments or when individuals are not fully adapted to environment
- > 2x chromosomes = 2x mutations
- > mutations can be masked in heterozygotes and not exposed to selection (i.e. geneotype could be different but pheotype is the same)
- > deleterious may be beneficial in different environments
- > beneficial may not be positively slected for until reaches sufficient frequency by chance events (drift)
advantages of being haplodiploidy
- > different stages in different environments = different selective pressures
i. e. haploid in stable environment, diploid in variable environment - > removes competition between stages
- > during asexual reproduction one stage can persist during unfavorable times while the other dies off
why are large, complex organisms typically diploid
- > more cells = more chance of mutation
- > somatic mutations masked in diploid organisms, but can be lethan in haploid organisms
* if mutation is deleterious, diploids still have a second copy to potentially mask the effect- haploid stages do not
