Chapter 42 Textbook notes

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Published on 1 Feb 2011
Biological Sciences
How do animals reproduce without sex?
Sexual reproduction is universal in almost all organisms
Some can reproduce sexually and asexually and some can only reproduce
Offspring that are reproduced asexually are identical to each other and parents
oCan convert resources to reproduce
oDon’t have to look for a mate
oBut does not have the genetic diversity that comes with sexual
reproduction which is a disadvantage in changing environments
Animals that reproduce asexually are usually invertebrates
oAre sessile
oCan’t look for mates
oDon’t have mates around
oLive in constant environment where reproducing asexually would be
Three ways animals reproduce asexually is by
1. budding,
2. regeneration
3. parthenogenesis
Budding and regeneration produce new individuals by mitosis
Budding—new individuals form as outgrowths or buds from older animals
oBud formed by mitosis
oBud is identical to parent
oCan grow to be as big as parent before being independent
oUsually thought as replacing damage tissue or lost limbs
oBut some organisms can regenerate to a new individual
oIf you cut a sea star into individual pieces then each piece will become an
individual organism
oThe development of unfertilized eggs
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oOccurs in arthropods and some fish, amphibians and reptiles
oSome species parthenogenesis determines sex—honey bees, males come
from unfertilized eggs, females come from fertilized eggs
oParthenogenesis sometimes requires sexual behaviour—like in whiptail
All are female
Some will act like male to stimulate another female to release eggs
Whether they act like a male or female depends on hormonal states
—when estragon levels are high it acts female, when estragon
levels go down and progesterone levels go up, then it acts male
42.2 How Do Animals Reproduce Sexually
Large portion of time and energy budgets of sexually reproducing animals goes
into mating
oMating exposes them to predators and usually takes a lot of energy, also
keeps them from doing other things like feeding and taking care of
existing offspring.
Sexual reproduction requires 2 haploid cells to come together to make a diploid
oHaploid cells are also called gametes
oGametes are formed by gametogenesis
Sexual reproduction has 3 parts
oGametogenesis (making gametes)
oMating (getting gametes together)
oFertilization (fusing gametes together)
Gametogenesis produces eggs and sperm
Gametogenesis happens in the gonads—testes in males and ovaries in females
Gametes formed in males are sperm and eggs in female
Sperm moving using a flagellum and eggs are non-motile
Gametes form from germ cell—different from other cells in the body which are
somatic cells
Germ cells are secluded in the body until gonads start to form
Then germ cells go to the gonads and by mitosis become spermatagonia and
oogonia which are diploid
They multiply by mitosis and become primary spermocytes and primary oocytes
Then through meiosis the chromosomes reduce to haploids—these become sperm
and ova
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