Transcript asexual reproduction teacher copy

Reproduction & Development
I. Selective Forces
-- all of evolution is based on reproduction
-- to persist through evolutionary time, animals must put copies
of their genes into the next generation
-- for sexual reproduction, fertilized egg must develop into
surviving offspring
Reproduction
II. Asexual vs. Sexual Reproduction
A. Asexual reproduction
-- only one parent
-- no reproductive organs
-- no meiotically produced gametes (sex cells); no fertilization or
zygote formation
-- offspring are genetically identical to parents (clones)
Reproduction
II. Asexual vs. Sexual Reproduction
A. Asexual reproduction
1. advantages
-- pass on 100% of genome to each offspring
-- all individuals can produce offspring directly
-- can occur rapidly; rapid exploitation of resources
-- saves energy and resources (no gonads or gametes, no finding mates,
no courtship, no STDs, no males)
2. disadvantages
-- no genetic variability in offspring (except for random mutations)
-- limited ability to respond to changing environment
Reproduction
II. Asexual vs. Sexual Reproduction
B. Sexual reproduction
-- usually involves two parents
-- reproductive organs
-- haploid gametes produced by meiosis; fertilization  diploid zygote
-- offspring are genetically unique
1. disadvantages
-- pass only 50% of genome to each offspring
-- energy expended for gonads and gametes
-- production of males (many fail to mate)
-- is complicated; occurs more slowly
-- requires finding mates, courtship,
-- STDs
2. advantages
-- increased genetic variability in offspring
-- ability to respond to changing environment, esp. biotic environment
Alternation of Asexual and Sexual Reproduction: ex: Fasciola (sheep liver fluke)
miracidium
egg
Sexual adult in
sheep liver
metacercaria;
encysted on vegetation
Asexually produced cercaria;
leave snail
asexual redia
in snail
Reproduction
III. Mechanisms of Asexual Reproduction
A. Fission: animal divides by mitosis
Binary fission
Paramecium
Multiple fission
Plasmodium
Binary Fission
Asexual
Cell splits and replicated DNA
goes with each part
Prokaryotes, Bacteria
+ Fast and easy
- Everybody has the same DNA
Bacterial
Conjugation
Asexual “Sex”
A bacteria shoots out a
tube and sends a piece
of its DNA to another
bacteria
Bacteria
+ Mixes DNA
- “Parent” loses a little
piece of DNA
Fragmentation/ regeneration
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Asexual
Body of parent
breaks and
produces
offspring
Fungi, moss, sea
stars, planarian
+ Easy
- Parent broken,
same DNA
Fragmentation/ regeneration
Reproduction
III. Mechanisms of Asexual Reproduction
B. Budding:
new individual arises from outgrowth of parent
Reproduction
III. Mechanisms of Asexual Reproduction
C. Gemmulation: Poriferans
-- formation of new individual from aggregation of asexual
cells encased in resistant capsule (= gemmule)
Reproduction
III. Mechanisms of Asexual Reproduction
D. Fragmentation:
-- formation of new individual from fragments of parent