biol1008

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Author:
pink_m666
ID:
98562
Filename:
biol1008
Updated:
2011-08-27 01:30:55
Tags:
sex
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  1. What is sex?
    • mode of reproduction
    • behaviours associated with copulation
    • 'sex' sometimes used to describe maleness or femaleness
  2. Asexual Reproduction
    • sex is not necessary for reproduction
    • self fertilisation can occur eg in plants: males and female flowers in the one plant
    • many adaptations to prevent self fertilisation
  3. What is a disadvantage for asexual reproduction?
    no genetic variation
  4. What is a fission?
    the separation of a parent organism into two individuals of approximately equal size
  5. budding
    new individuals
  6. parthenogenesis
    • form of preproduction in which the ovum develops into a new individual without fertilisation.
    • e.g. bees and wasps: females are diploid adults that develop from fertilised eggs. Males are fertile haploid adults that arise by parthenogenesis
  7. What is sexual reproduction?
    • reproduction that generates a new individual combining the genes of two parent individuals
    • fusion of the haploid (n) gametes = diploid (2n) zygote. consists of 2 sets (2n=46)
    • male gamete = sperm
    • female gamete = ovum/egg/oocyte (usually larger than sperm)
    • gamete also called germ cell
  8. What is the only universal truth about sex?
    parthenogenesis can occur many ways but in sexual reproduction meiosis is always the same.
  9. Costs of Sex
    • recombination scrambles genotypes, disrupting favourably adapted gene combinations
    • parthenogenesis preserves advantageous genotypes
    • meiosis and sngamy takes longer than miotosis, slowing the pace of reproduction
    • decreased population growth rates
    • in higher organisms, courtship and mating is risky (risk from predation, STD's, wastage of gametes, costs associated with maintenance of sexual dimorphism, sexual competition)
    • at low population densities sexual reproduction may be difficult to coordinate
    • parthenogenesis ensures that reproduction will be possible at any time
  10. advantages of sex?
    • DNA repair
    • Recombination (sex) purges deleterious mutations
    • facilitating response to environmental change
    • parthenogenetic organisms more easily attacked by parasites
    • sex is needed to fight disease
    • allows selection to more easily work on combinations of traits
    • allows genome of species to carry significantly more information than genome of an individual
    • encourages fruitful collaborations
    • asexually producing species often thrive for a time but are slower to adapt to change
    • many organisms only reproduce sexually only in times of stress, reproduce asexually normally
  11. What is gender?
    • Gender assignment needs to take into account all three of the following aspects:
    • chromosomal makeup
    • internal organs
    • external genitalia
  12. How is gender det

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