Download Reproduction and Development

Reproduction and Development
Asexual Reproduction: reproduction without gametes
Common in protozoa and in invertebrate animals
Binary fission: division of a parent into two or more individuals
Budding: offspring are outgrowths of parents
Fragmentation: animal breaks into two or more parts
each fragment can become a individual
RESULT: offspring are identical
to parent (no genetic variation)
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Sexual Reproduction: reproduction with gametes
Present in all groups of animals
Bisexual reproduction: involving the union of gametes
from two genetically different parents
RESULT:
offspring are a new combination of both parents
Fertilization depends on mechanisms that help
sperm meet eggs of the same species
Things to consider:
Sperm must be able to find an egg
Gametes need a moist environment
(to prevent drying out and help sperm swim)
Two approaches:
External fertilization: release of gametes into
the surrounding environment
Requirement: timing! ensure sperm encounters eggs
Internal fertilization: Sperm is deposited in or near the female reproductive
tract and fertilization occurs in it
Requirement: cooperative behavior between male and female
structural adaptations for delivering sperm
Solution: use of environmental cues, pheromones, and/or
courtship behavior (involves species recognition , female choice,
male-male competition )
Advantages and disadvantages of each type of fertilization ?
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Why do so many animals reproduce
sexually rather than asexually?
sexual reproduction
asexual reproduction
Investment of energy and time
Genetic variation
Environment type favored
changing vs stable environment
colonization vs crowded
Reproductive patterns
Animals may reproduce exclusively asexually
or sexually,
or they may alternate between the two modes
Hermaphroditism : An animal that has both sexual organs
Beneficial to animals that are sessile , burrowing or
endoparastitic
In reef fish and oysters, sequential hermaphrodites
changes its sex with age and size
Wrasses: female first, male live in harems
In clown fish male first
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Reproductive patterns
Parthenogenesis: development of an embryo
from a unfertilized egg (can be diploid or haploid)
Beneficial when environment is stable
In aphid and Daphnia, as a response to seasons or stress
During environmentally stable times  eggs ___________
During environmental stress  eggs _____________
In bees, wasps and ants, role in social organization
Fertilized eggs  queens and sterile workers
Unfertilized eggs  males drones
Reproductive patterns
Oviparous (egg-birth)
eggs are laid outside of body for development
fertilization may be internal or external
may show various degrees of parental care
Ovoviviparous (egg-live-birth)
eggs are retained inside but embryos derive all
nourishment for yolk inside the egg
common earthworms, insects, sharks and snails
and in some reptiles
Viviparous (live-birth)
eggs develop inside deriving their nourishment
directly from the mother
mostly in lizards, snakes, mammals and sharks
but also in scorpions
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Animal development: Fertilization
Animal development: Cleavage (one layer embryo)
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Animal development: Gastrulation (two-layers)
Animal development: Formation of a
third layer of cells and a complete gut
and in some a second cavity
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Animal development: the fate of cells in Germ layers
Embryo development provides information about how
animal groups are related
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