Topic 5: The Protists: Diversification, Lifecycles, and Reproduction

-photoautotroph

-brown, green, and red algae

-very important ecologically( with phytoplankton account for over 50% of global photosynthesis)

-sexual and asexual

-meiosis and mitosis

-complex life cycles

-three main eukaryotic sexual life cycles (all in protists)

-figure 13.6

-"haplontic" or "zygotic meiosis" (because zygote goes through meiosis which limits diploid stage to zygote only)

-found in many protists and all fungi

-only one cell type is diploid (zygote)

-ancestral to other two cycles

Gametes (n)- Fetilization- Zygote (2n)- Meiosis- (n)- Haploid unicellular or mulicellular organism (n)- Mitosis- Gametes (n)

-"alternation of generations" or "sporic meiosis" (because products fo meiosis are spores)

-Sporophyte: diploid stage and produces haploid spores

-Gametophyte: haploid stage and produces haploid gametes

-found in some protists and all plants

-gametophytes small but multicellular

-male and female gametes different morphology

-zygote supported by female gametophyte

-spores are flagellated

-"diplontic" or "gametic meiosis" (because products of meiosis are gametes)

-only one cell type is haploid (gamete)

-common in animals and found in few protists

Two Trends:

-gamete morphology becomes complex

-diploid becomes more prominent

-Isogamy

-Anisogamy

-Oogamy

-gametes are motile but differ in size

-female gamete is larger than the male gamete

-disruptive selection favours gametes...

    -capable of finding and fetilizing other gametes

    -capable of producing healthy zygotes

-female becomes larger and non-motile

-fewer female gametes produced

-some with nourishment in for embryo

-evolved independently in several protists, in all plants, and in all animals

-fitness advantage with offspring survival

-in species where females accept multiple mates

-selection on sperm morphology and function

-increase chances of male fertilization success when in competition with other males

-diploidy was a DNA replication error or fusion of two haploid cells

-meiosis protects against further errors (homologous chromosomes line up and "crossover safely")

-sex accumulates beneficial mutations faster-especially in large populations

-sex eliminates harmful mutations faster (in asexual-offspring have as many of more mutations than parent; in sexual-offspring can have more or less mutations than parent)

-97% of eukaryotic species use sex

-"sexual selection" for "attractive" traits=fitness can be high for some

-sex increases genetic variation (crossover, recombination...)

-sex promotes heterozygosity (protection from harmful alleles)

-known in all eukaryotic groups (and pro.)

-often in constant/predictable environments

-higher fitness to make clones

-form of asexual reproduction

-can result form hybridization, polyploidy, or embryo from unreduced egg or other cell

-can have diploid (homozygous) offspring without