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56 Cards in this Set
- Front
- Back
For sex organism does not need |
sex organs or multicellularity |
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Requirements for sex |
diploid phase of life, meiosis, union of haploid meiotic products |
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origination of eukaryotic sex |
in unicellular organisms |
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syngamy |
fusion of two cells, or their nuclei, in reproduction |
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fertilization |
union of egg and sperm to create a fertilized egg called a zygote |
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Haplontic Life Cycle |
only diploid for one meiotic cell cycle |
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Mature organism in haplontic life cycle |
haploid (n) |
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Only diploid in haplontic life cycle |
zygote (2n) |
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Haplontic organisms |
most protists, fungi and some green algae |
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Features of haplontic sex |
cells spend most of their life as haploids, sex optional, zygote immediately undergoes meisos, no stable diploid phase at all |
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Alternation of generations life cycle |
organism passes through haploid and diploid stages that are both multicellular |
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Alternation of generations organisms |
most plants and some fungi |
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Diploid stages in alternation of generation life cycle |
zygote and sporophyte |
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Haploid stages in alternation of generations life cycle |
spore, gametophyte, and gametes (male and female) |
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gametophyte |
gamete producing and usually haploid phase, producing the zygote from which the sporophyte arises. Dominate form in bryophytes |
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Feature of alternation of generations life cycle |
allows for extended periods of either ploidy |
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Diplontic life cycle |
only haploid stage is gametes |
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Diploid phases in diplontic life cycle |
zygote and mature organism |
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Diplontic organisms |
found in animals, brown algae and some fungi |
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weird sex in paramecium |
contains micronucleus and macronucleus, haploids exchange micronuclei and macronucleus disintegrates |
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micronucleus |
contains complete genome in one or two copies |
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macronucleus |
many copies of active genes only |
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Anisogamy |
in multicellular organisms, large and small gamete |
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Isogamy |
protists gametes are the entire organism, same size but different mating type |
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Cost of males |
disadvantage of anisogamous sex- eggs provide nearly all material for zygote, reproduction is female limited |
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cost of meiosis |
disadvantage of anisogamous sex- meiosis and outcrossing costly even without dedicated male sex. Sexual females only half as related to offspring as asexual females |
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Dandelion sex |
dandelions became asexual, essentially all angiosperms outcross, sex was feature of first angiosperms |
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Bdelloid Rotifers |
no males- reproduce by parthogenesis |
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Benefits of sex |
1. increasing genetic diversity allows for adaptation to ever changing environments (red queen- parasites or hosts) 2. sex allows for faster adaptation- beneficial alleles can be combined more quickly 3. eliminates harmful mutations |
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Outcrossing and males |
increase in frequency after stress |
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Sex after stress |
under stressful conditions progeny of crosses do better than those that come from self fertility |
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Gonochrism |
2 sexes- male and female, development must be regulated to prevent intersexual forms (often by sex chromosomes) |
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hermaphroditism |
1 sex- makes sperm and eggs, common in animals |
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monoecy |
1 sex- hermaphrodite with separate male and female flowers |
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selfing |
1 sex- hermaphrodite (not mating) |
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gynodiecy |
2 sexes- hermaphrodite and female |
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androdioecy |
2 sexes- hermaphrodite (selfing) and male |
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parthogenesis |
1 sex- female (no males) |
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outcrossing between hermaphrodites |
the norm in angiosperms |
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evolution of mixed strategies in plants |
ancestor of angiosperms was hermaphroditic, male and female sexes evolve by loss of floral organs for opposite sex, androdiecy exists but very rare |
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Why evolve selfing? |
selfing is handy when mates are scarce |
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Animal life cycles can mix outcrossing and |
asexuality- ie daphnia. As weather cools or food limited sexual morphs are made which produce resistant resting eggs viable long term |
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Complete commitment to asexuality |
ie cnedimepherous uniparens lizards- formed by corss between two species with different chromosome numbers, can't do meiosis. Parthogenesis may be spontaneous solution to keep lineage alive |
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Asexual reproduction without embryos |
budding, cloning, fragmentation (ie root cloning) |
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Chytrid (water) fungi |
haplodiplontic and include only fungi in which alternation of generation occurs. |
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Features of chytrid sex cycles |
make motile spores and gametes (only fungi which do), gametes moderately anisogamous, female gametes release a pheremone that attracts male gametes. Zygote forms small diploid myecelium before meiosis and sporulation. |
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Non-chytrid (terrestrial) fungal life cycles |
haplontic and isogamous |
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Non-chytrid features of sex cycles |
haploid spores form by mitosis or meiosis, gametes remain attached to mycelium, many cell cycles pass between gamete membrane fusion (plasmogamy) and nuclear fusion (karyogamy). Karyogamy essential before meiosis |
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Plasmogamy |
stage in sexual reproduction of fungi in which cytoplasm of two parents cells (usually from mycelia) fuses together without fusion of the nuclei, effectively bringing two haploid nuclei closer together in same cell |
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Karyogamy |
final step in the process of fusing two haploid eukaryotic cells, and refers specifically to the fusion of the two nuclei. Before karyogamy, each haploid cell has one complete copy of organisms genome. |
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heterokaryon |
multinucleate cell that contains genetically different nuclei. |
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Basidiomycota life cycle features |
in soil heterokaryotic mycelia form and produce mushroom, in gills haploid nuclei fuse, go meiotic and make spores, spores launched as buds from basidium |
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Ascomycota life cycle features |
have reproductive structures with many spore producing asci. heterokaryosis mycelia form and make spore producing organ. haploid nuclei fuse, go meiotic and make eight spores. spores burst from ascus |
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Migration onto land of fungi |
altered reproduction from haplodiplontic/anisogamous to haplontic and isogamous. Negligible embryonic development and gametes cant swim. Seperation of plasmogamy and karyogamy occured and evolution of special fruiting bodies for spore dispersal on land. |
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embryos need stuff |
hypothesis for anisogamy- most multicellular organisms build offspring via an embryo, the zygote must be big enough to support development of functional multicellular organism before it can feed, total mass must come from two gametes that fuse |
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motility essential for fertilization? |
hypothesis for anisogamy- multicellular organisms are typicall much bigger and much further apart than protists, gametes will have to find each other over tens to hundreds of meters, random impacts will almost never occur |