Sexual reproduction Flashcards
reproduction success meaning
determined by its ability to produce fertile offspring that survive to reproductive maturity: measured by the individual
biological fitness meaning
how likely alleles will be present in future generations: measured by the allele
two types of reproduction
asexual and sexual
process of sexual reproduction
two haploid gametes fuse in a process called fertilisation to create a zygote; offspring has mixed genetics- one set of paternal chromosomes and one set of maternal chromosomes
advantages of sexual reproduction
- introduces genetic variation
- offspring may gain a selective advantage
disadvantages of sexual reproduction
- requires a greater expenditure of time + energy
- requires more investment by an individual than asexual reproduction
unisexual meaning
animals which are separate male and female individuals
hermaphrodite meaning
animals in which individual has both male and female reproductive organs
hermaphrodite better for
low population densities or non-motile
hermaphrodite disadvantage
less genetic variation + larger energy expenditure to grow + maintain two sets of reproductive organs
fertilisation
in which gametes meet, and do not get dehydrated in the process
external fertilisation
occurs outside the body, more suited to aquatic/moist environments
internal fertilisation
occurs within the body, suited to terrestrial organisms
summary on external fertilisation
- external = less time + energy for parents, but more gametes to ensure young survive
- usually results in less parental care for young
- release of gametes and distribution via biotic/abiotic factors results in less competition for food + living space
- can be synchronised over species using environmental cues or pheromones
amphibians’ reproduction
life cycle involves both land and water
- most amphibians: gametes released in fresh water; lack of parental care, tadpoles = easy prey
- some frogs: eggs fertilised externally but swallowed by female; extreme parental care increases survival chances
summary of internal fertilisation
- internal: protects gametes from dehydration + immediate predation
- requires fewer gametes for sufficient no. of offspring
- usually means less offspring + more parental care to ensure survival of offspring
oviparous
development in which internally fertilised egg develops shell and laid in external environment
eviviparous
development in which fertilised egg becomes embryo, nurtured in female’s body, nutrients through placenta, born alive
ovo-viviparous
development in which eggs with yolk for nourishment retained inside mother’s body + hatched, newly hatched young are born alive
reptiles
most have eggs that are fertilised internally, then deposited outside mother’s body
- eggs can be hard-shelled or soft and leathery
birds
internal fertilisation preceded by courtship
- once egg fertilised, laid with calcium carbonate shell that hardens with contact with air, incubated by parents to maintain warmth
- hard egg = protection, parental care
mammals
all undergo internal fertilisation
monotremes
oviparous; after internal fertilisation, eggs develop outside mother’s body
- e.g. platypus + echidna
marsupials
offspring develop internally for short time after fertilisation before continue development in pouch
- can have three offspring in different stages of development at once: one out of pouch, one in pouch, one fertilised ovum in uterus
embryonic diapause
development of youngest triggered when second-youngest detaches from pouch, delay in embryo development
eutherians
placental mammals, offspring develops inside mother’s body with placenta
- placenta gives nutrients, diffuses waste
- few young but massive investment
angiosperms vs gymnosperms
angiosperms: flowering plants
gymnosperms: conifers
flower
reproductive organ in plants, contains male or female parts or both
female angiosperm reproductive parts
carpel
- Stigma: sticky surface, where pollen goes
- Style: joins stigma to ovary
- Ovary: where ovules are formed, develops into the fruit
male angiosperm reproductive parts
stamen
- Anther: where pollen is formed
- Filament: stalk that carries anther; length determines pollination method(longer for wind, shorter for insects)
cross-pollination
relying on outside agents to transfer pollen from anthers to stigmas
pollination by abiotic factors
inefficient + effective; requires large amounts of energy to make a lot of pollen
- used by conifers
- e.g. white cypress pine
pollination by biotic factors
reduces wastage of pollen, right flower pollinated
- efficient to have mutualist relationship with animal
- reward for pollination = fruit or nectar
- insects/animals attracted to color + nectar
- used by angiosperms
- e.g. bottlebrushes
seed dispersal
occurs after pollination + fertilisation
- seeds: fertilised ovules from inside ovary
advantages of wide distance dispersal of seeds
prevents overcrowding + competition for resources, increases chance of continuity of species in other locations
germination
development of plant from a seed or spore after period of dormancy
- plant embryo: dehydrated + dormant, survives adverse conditions until it lands in sufficient environment for growth
- develops radicle(young root) for water + nutrients and plumule(young stem) to grow leaves for photosynthesis
