Life Cycles
and Reproduction
Housekeeping!
Binary Fission – a from of asexual
reproduction that produces identical
daughter cells
• Bacteria undergoing Binary Fission
• Another view of bacteria reproducing
• An explanation with Ameoba
Conjugation – a form of sexual
reproduction
• Bacteria conjugating & paramecium conjugating
(results in an exchange of genetic material)
With Eukaryotes and especially
multicelluar organisms things get more
complicated
• Sexual reproduction involves specific sex cells
(egg and sperm cells) called gametes
• Gametes are haploid (n) – contain only 1 set
of chromosomes
• When an egg & sperm cell fuse they form a
zygote, which becomes diploid
• Diploid cells (2n) contain 2 sets of
chromosomes – one set inherited from each
parent cell
How are haploid and diploid cells
formed
• Diploid cells
created through
mitosis
• (e.g. Body or
somatic cells)
• Haploid cells
created through
meiosis
• (e.g. Egg &
sperm)
Mitosis
Meiosis
Sexual Life Cycles
• There are 3 different types of sexual life cycles
– Gametic
– Zygotic
– Sporic
• All cycles alternate between meiosis, which
makes sperm and eggs, and fertilization,
which merges sperm and egg to create a
zygote.
Sporic life cycle
Sporic life cycle
• Ex. of an alteration of generations
= a life cycle in which diploid
individuals (sporophytes) produce
spores that create haploid
individuals called gametophyes
• Haploid individuals reproduce
sexually, producing sporophytes
• Spore = a haploid reproductive
structure, usually a single cell,
capable of growing into a new cell
• E.g. Brown algae, all vascular
plants
Zygotic Life Cycle
Zygotic Life Cycle
• Zygotes is the only diploid
cell ever
• Meiosis occurs in the zygote
to produce spores
• Spores germinate to
produce vegetative phases
that are haploid
• Organisms with this type of
lifecycle are algae and fungi
• E.g. Life cycle of a
basidiomycete (i.e.
Mushrooms)
Gametic Life Cycle
Asexual Life Cycle