Zygote diploid 2n cells from the single celled zygote

zygote: diploid 2n cells)
 from the single celled zygote stage onward, cells undergo mitosis
to increase the number of cells in the maturing individual
(multicellular individuals; diploid 2n cells)
o The life cycle of fungi (bread mold); representing simple life cycle for multicellular
sexually reproducing haploid organism
 Carrying one copy of genome, multiple rounds of asexual reproduction
possible, all cell divisions occur by mitosis (haploid 1n cells of hyphae)
 Brief intergenerational zygote stage: fusion of compatible hyphae
(plasmogamy and karyogamy) to form a zygote-like structure (diploid 2n
zygote)
 Zygotic meiosis  haploid 1n spore
 Multiple rounds of asexual reproduction possible, all cell divisions occur
by mitosis (haploid 1n cells of hyphae)
o The life cycle of plants (dioecious flower); representing a complex life cycle for
multicellular, sexually-reproducing, organism with alternation of generations
 Multicellular sporophyte (diploid 2n cells) undergo meiosis to produce
spores
 Unicellular spores undergo mitosis to increase the number of cells in the
maturing gametophyte (multicellular gametophyte, haploid 1n cells)
 Mature gametophyte produces gametes by mitosis (unicellular gametes)
 Gametes fuse during fertilization to become a zygote (unicellular zygote)
 multicellular sporophyte (diploid 2n cells)
 Specialized cells undergo meiosis to produce spores (unicellular spores of
gametophyte (haploid 1n cells)
 Allocation Trade-offs, costs & benefits, constraints
o Whether or not a particular life-history trait is favored by natural selection
depends on the benefit/cost ratio
o “there is no free lunch” meaning no organism can invest unlimited amounts of
energy in growth and reproduction… “a jack of all trades is a master of none”
o trade-offs occur when organisms allocate their limited energy or other resources
to one structure or function at the expense of another
o Trade-off between size and number of offspring (offspring or propagule size-
number tradeoff)