Chapter 16 Flashcards
Environmental unpredictability model, why does it favor sexual reproduction?
Sexual reproduction should be seen more often in rapidly changing environment; offers great deal of variation allowing for better adaptability to unpredictable environments
Number of niches, why does it favor sexual reproduction?
S.R. will be favored in niche-rich environments because of the potential for large numbers of new genotypes capable of colonizing new niches
-lakes have greater # of eco-niches
Red Queen Hypothesis
Frequency of S.R. will be related to the level of PARASITIC infection. Sexual reproduction creates a moving target for parasites= parasite resistant genotypes may result
Asexual reproduction
Production of offspring from unfertilized gametes from a single female parent
Apomixis
Unfertilized gamete undergoes a single mitosis-like cell division, producing two “daughter cells”. Each daughter cell has an UNREDUCED number of chromosomes and is genetically identical to its mother
Automixis
Haploid gametes produced via MEIOSIS but diploidy is usually restored by the fusion of haploid nuclei from the same meiosis. Offspring is genetically different from parent and siblings, but MUCH LESS than sexual reproduction.
Sexual reproduction
The joining together of genetic material from 2 parents to produce an offspring that has genes from each parent
Amphimixis
characterizes sexual reproduction; but with alternating phases of meiosis and gamete fusion
Syngamy
alternating phases of meiosis and gamete fusion
Recombination
The crossover between homologous chromosomes, which produce new chomosomal events
Gametes production
The production of haploid gametes by diploid individuals via reductive meiotic division
Gamete fusion
The gametic exchange between (usually) UNRELATED individuals, in which haploid gametes fuse to produce a diploid offspring
Does genetic exchange in bacteria constitute as sexual reproduction?
NO
How do you distinguish between sexual and asexual reproduction?
Observing genetics (presence/ absence of reproductive genes like homologs) & Comparing phylogenetic trees (asexual will have a more congruent tree when comparing nuclear and mt genes)
Asexual reproducing species tend to go extinct more quickly or less quickly than sexual species?
More quickly!
Are there a lot of taxa (genus or higher) that are entirely composed of Asexual species?
Almost none.
Where have all asexual species thought to have evolved from?
Sexually reproducing ancestors
What is the genetic cost of asexual reproduction?
Asexual females are twice as genetically related to their offspring as are sexual females
What is the advantage of asexual repro?
Population in ASR increases twice as quick, as a consequence of anisogamy
Anisogamy
When female produces TWO LARGE gametes & males reproduce a lot of small sperm. (male’s effort is basically wasted)
Isogamy
Each parent produces mid-sized gametes
How is asexual more “expensive”
Twofold cost of sex (cost of males)
How can sexual reproduction come at a cost?
Can break up favorable gene combinations (recombination)
Benefits of sexual reproduction (3)?
- Can purge deleterious mutations
- Generates genetic variation that is favored by natural selection
- Combination of both
Muller’s ratchet
Number of deleterious mutations will INCREASE; not equivalent to a deleterious mutation becoming fixed
sexual reproduction reverses ratchet
Two facts on Y chromosome
- Doesn’t undergo recombination
- Has been degenerating and accumulating deleterious mutations
Epistasis
Interactions between the effects of alleles at different loci
Synergistic mutations
Two mutations occurring together have more of a detrimental effect
Fisher-Muller Hypothesis
Recombination allows natural selection to operate at a quicker rate than is possible in asexual species
Linkage disequilibrium
If two genes are in linkage disequilibrium, it means that certain alleles of each gene are inherited together more often than would be expected by chance. (This may be due to actual genetic linkage–that is the genes are closely located on the same chromosome.)
sex breaks down link-disequi.
What is the evidence that sex accelerates adaptive evolution?
Yeast and green algae; in a harsh environment, sexual strains increase in fitness faster than do asexual strains
“bet hedging”
Increases the chance that at least one of an individual’s offspring will be a good match to the environment.
Cyclical parthogenesis
Usually reproduce asexually, but occasionally reproduce sexually
What is the hypothesis on the origin for sexual reproduction?
Means for transposable genetic elements to spread from cell to cell.
Also, mechanism for DNA repair
transposable genetic elements
is a DNA sequence that can change its position within the genome, sometimes creating or reversing mutations and altering the cell’s genome size
