Lecture 8: The Evolution of Sex Flashcards
What is the definition of Outbreeding?
Outbreeding is the mating between individuals that are less related than the average relatedness in the same population, typically referring to matings between unrelated individuals
What is the significance of Outbreeding?
Creates a greater average heterozygosity; more variation among offspring
What is the definition of Inbreeding?
Inbreeding is the mating between individuals that are more closely related than the average relatedness in the same population, typically referring to matings between very closely related individuals
What is the significance of Inbreeding?
Creates a greater average homozygosity; less variation among offspring
Increase in the % mortality of offspring because deleterious traits can become fixed
Are most organisms sexual or asexual?
Sexual (undergo sexual selection at least on occasion)
Describe the taxonomic distribution of asexual lineages?
Sporadic; asexual organisms are evolutionarily short-lived (i.e. become extinct)
What is the definition of Cyclic Sexuality?
The cycling between sexual and asexual reproduction within an individuals lifecycle
What is the significance of Cyclic Asexuality?
Being sexual/asexual during specific times can be advantageous (unstable conditions may require genetic variation)
What does sex do?
Gene exchange and recombination through zygote formation/the formation of a temporary diploid stage
How can recombination occur?
- Crossing-over between homologous chromosomes during meiosis
- Independent assortment of chromosomes during meiosis
What is a consequence of recombination?
An increase in genetic variation/diversity between gametes and offspring
What are the disadvantages to sexual reproduction?
- Cost of meiosis (i.e. cost of producing males)
- Need to find sexual partner
- STDs
- Mixing of female genes with mutated male genes
- Breaking up co-adapted gene complexes
What is the definition of the Cost of Meiosis?
The Cost of Meiosis is the 50% chance of elimination for any allele that codes for sexuality; the cost of producing males
Why is asexual reproduction advantageous when looking at the Cost of Meiosis?
Asexual females have 2x the reproductive rates of sexual females because asexual females don’t waste resources on sons
How do females poison their own, relatively unmuted genes with bad, mutated genes from males?
Most mutations arise from males and not females due to a greater number of meiotic divisions during spermatogenesis than oogenesis
What are the advantages of sexual reproduction?
- Faster elimination of deleterious mutations
2. Faster evolution (bringing favorable mutations together in the same individual)
Describe the Muller’s Ratchet Model.
Asexual lineages accumulate deleterious mutations (i.e. mutational meltdown) and the least-mutated genotype is eventually lost for forever
Sexuality can restore the least-mutated genotype through recombination in a sexual population because the most-mutated genotypes are selected against
Why does sex facilitate faster evolution than asexual reproduction?
In asexual populations, different colonies compete with one another (i.e. colonial interference)
Did recombination arise originally as a mechanism for DNA repair?
The reason for the origin of sex (e.g. DNA repair) may have been different than the reasons for the maintenance of sex (e.g. faster evolution, elimination of deleterious alleles)
What are the 2 principle ways of making gametes?
- Few, large gametes
2. Many, small gametes
What is the advantage to few, large gametes?
Increase in zygote survival/resources; high parental investment
What is the advantage to many, small gametes?
High motility increases likelihood of pairing; low parental investment
What is the definition of Anisogamy?
Anisogamy is the production of small and large gametes which coexist in the same population
What is the significance of Isogamy?
Isogamy is the production of same sized gametes in the same population
What is the female function in sex? The male function?
Female function: high reproductive effort
Male function: high mating effort
What limits fitness for females? For males?
Female fitness: resources acquired
Male fitness: access to mates
What type of selection is favored for gametes?
Disruptive selection
What are the consequences of initial inequality?
- Male-male competition (intra-sexual selection)
2. Female choice (inter-sexual section)
Characteristics of the sex with high parental investment?
Choosey when selecting males (i.e female choice)
Characteristics of the sex with low parental investment?
Will fight with other males for males (i.e. male-male competition)
What is the definition of Sex-Role Reversal?
Sex-Role Reversal is the increase in paternal investment in each offspring
