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What is sex?
- mode of reproduction
- behaviours associated with copulation
- 'sex' sometimes used to describe maleness or femaleness
- 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
What is a disadvantage for asexual reproduction?
no genetic variation
What is a fission?
the separation of a parent organism into two individuals of approximately equal size
- 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
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
What is the only universal truth about sex?
parthenogenesis can occur many ways but in sexual reproduction meiosis is always the same.
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
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
What is gender?
- Gender assignment needs to take into account all three of the following aspects:
- chromosomal makeup
- internal organs
- external genitalia