1114 Chapter 8

  1. Asexual Reproducton
    • Formation of offspring without the fusion of egg and sperm
    • The offspring genetically identical to parent
  2. Sexual Reproduction
    • Formation of offspring by fusion of a female gamete (egg) with a male gamete (sperm)
    • Offspring inherit features from both parents, not identical to either
  3. Evolution will not occur in a population if
    • Mating is random
    • No natural selection
    • No mutation
    • Large population size
    • No migratoin
  4. Types of asexual reproduction
    • Budding
    • Fission
    • Parthenogenosis
  5. Budding
    Offspring develop as outgrowth of parent
  6. Fission
    Parent splits into two organisms of roughly equal size
  7. Parthenogenosis
    • Unfertilized eggs develop into offspring
    • Whiptail lizards: the entire species is female -> reproduce this way
    • They still display courtship/mating behaviors -> associated with hormone levels during breeding season
    • Females mounted by "male-like" females more likely to ovulate and lay more eggs
  8. Asexual reproduction vs. sexual reproduction
    • Asexual: 
    • -All individuals can bear offspring
    • -Reproduction NOT limited by number of females
    • -More offspring by Generation 4

    • Sexual:
    • -Half of the individuals can bear offspring
    • -Require 2 individuals to produce offspring
    • -Reproduction limited by number of females
  9. Reproduction in isolation?
    • Asexual: yes
    • Sexual: no, must find a mate
    • -Isolation or inability to attract a mate limits reproductive output
  10. What evidence do we have that sex is evolutionary advantageous?
    • Ubiquity: seen in most eukaryotes (prokaryotes also have modes of recombination)
    • Historic Extinction Rates: asexual lineages have higher extinction rates because if there is a lethal disease then there will be no adaptation.
  11. How can beneficial alleles be spread through asexually vs. sexually reproducing populations?
    • Asexual: offspring are clones of parents, so beneficial alleles not combined in offspring.
    • Each lineage would have to independently gain beneficial alleles since mutation is random, it takes much longer

    • Sexual: Beneficial alleles rapidly combined in offspring. so it can spread through population quickly
    • Sex produces new combinations of alleles
  12. Why is variation beneficial?
    Variation allows population response to changing environment via selection
  13. Advantages of Sex
    • Variation
    • Fewer Deleterious Alleles (in asexual reproduction all mutations are passed to offspring)
  14. Mutation Meltdown
    • Over time in asexual populations, proportion of low fitness individuals with many deleterious alleles increases
    • -eventual consequence=extinction
  15. What explains greater extinction rates of asexual lineages?
    • Mutation meltdown
    • Lower variation
  16. If both parents are heterozygous have deleterious alleles, how many of the offspring will express the deleterious phenotypes?
    • In asexual reproduction, all of the offspring express both deleterious phenotypes.
    • In sexual reproduction, 56% of offspring will express both, 38% of offspring will express one allele, and 6% of them will express none
    • -In a dihybrid cross ~50% have lower negative allele proportion. The people without it will have higher fitness and reproduce
  17. Sexual Selection
    • Individuals with certain inherited characteristics are more likely than others to attract mates and therefore pass on their alleles at a greater frequency than individuals without those phenotypic characteristics
    • A form of natural selection
  18. Why is sexual selection typically males competing for females? (gamete production)
    • Female gametes: eggs are limiting, so females can produce limited number per breeding opportunity
    • Male gametes: excess of sperm, so they are not limited by sperm available during breeding season
    • Results in male skewed operational sex ration (OSR)
  19. Operational Sex Ratio (OSR)
    Ratio of males in populations that are ready to mate with females in that population that are ready to mate
  20. Why is sexual selection typically males competing for females? (parental care)
    • Parental care often falls on the female-- gestation, lactation, guarding, feeding. There is a greater energetic cost to raising young
    • Differential parental investment (PI): measured as each parent's contribution to rearing offspring
  21. Female mating strategy
    • Find a mate with beneficial alleles or good resources so offspring have better chance of survival
    • This is because gametes are limited with high PI
  22. Male mating strategy
    • Mate with as many partners as possible (and leave rearing to them if possible)
    • This is because gametes are not limited with low PI
  23. On average, which sex will have higher reproductive output (number of offspring)? (assuming roughly equal numbers of males and females in the population)



    A) Females and males will have the same average reproductive success

    If in a deer population produces 30 offspring, they all came from a male and a female
  24. Considering your knowledge of sexual selection, which sex will have greater variation in reproductive output among individuals of that sex?



    D) Males will have greater variation
  25. Why is female reproductive success relatively uniform?
    • Not limited by mating opportunities -> male strategy to gain as many mates as possible
    • Limited egg (gamete) resources -> fertilized
    • Limited by resources required to raise young
  26. Why is male reproductive success variable?
    • Limited by mating opportunities -> female strategy to mate with high quality mates only
    • Males that can demonstrate quality preferred
  27. Given this, selection will act more strongly on which sex?



    A) Selection will be strongest on males
  28. Why does selection vary?
    • Selection acts on variation: stronger in males because of greater variation in reproductive success
    • Selection for characteristics that allow greater access to mates
    • -Characteristics that allow defense of territories/resources and thus greater access/opportunity to mate
    • -Characteristics that result in greater female choice
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1114 Chapter 8
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