Reproduction and Life Cycles

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Reproduction and Life Cycles

• Applying ecology and youll be pleased to know
  that some sex is involved.

2
Figure 15.8 Some chromosomal systems of sex
determination
male heterogametic, female homogametic
male lacks sex chromosomes, female homogametic
male homogametic, female heterogametic
no sex chromosomes - male haploid, female diploid
Campbell Reece, 6th ed.
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Figure 12-13
The twofold disadvantage of sex, in general.
Asexual reproduction
Sexual reproduction
Generation 1
Generation 2
Generation 3
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Figure 12-13
The twofold disadvantage of sex, in general.
Asexual reproduction
Sexual reproduction
Generation 1
Generation 2
Generation 3
Is it more advantageous to produce daughters, or
sons? Why? ECOLOGY CONTEXT population
regulation issues? EVOLUTIONARY CONTEXT
fitness issues?
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Figure 12-14a-hypothesis
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Figure 12-14b-setup
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Figure 12-14c-results
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Take a step back and consider simple
reproduction mitotic division

• also called fission
• is a sexual, nonsexual process?
• results in change, no change in chromosome
  number?
• results in change, no change in ploidy?
• produces daughter-cells, spores, gametes,
  offspring ?
• Try these!

9
Take a step back and consider simple
reproduction mitotic division

• also called fission
• is a sexual, nonsexual process?
• results in change, no change in chromosome
  number?
• results in change, no change in ploidy?
• produces daughter-cells, spores, gametes,
  offspring ? (sometimes, it depends)
• Maybe not so simple after all!

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Figure 12-5-1
MITOSIS
Diploid parent cell
How many pairs of chromosomes does this organism
have?
Chromosome replication
What is the difference between a chromosome and a
chromatid?
Prophase
Nuclear envelope breaks downchromosomes
condense.
Metaphase
Individual chromosomesalign at the metaphase
plate.
Anaphase and Telophase
Sister chromatids separatenuclear envelope
re-forms.
Two diploid daughter cells of mitosis
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Figure 12-5-2
MEIOSIS
Diploid parent cell
What is homology in reference to chromosomes?
Chromosome replication
Prophase I
Tetrads form by thesynapsis of
homologouschromosomes.Crossing over occurs.
How many pairs of chromosomes does this organism
have?
Metaphase I
Homologous pairsalign at the metaphase plate.
Anaphase I and Telophase I
Homologous chromosomesseparate two haploid
cells result.
Meiosis II
Sister chromatidsseparate.
Four haploid daughter cells of meiosis
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Figure 12-7
A CLOSER LOOK AT THREE KEY EVENTS IN MEIOSIS
Centromere
1. Replication,
during
interphase.Sister chromatids are held together
byproteins along the chromosome armsand at
the centromere. Shown earlyprophase of meiosis
I, when chromosomeshave condensed.
Sister chromatids
Chromosomes
One homolog
2. Synapsis,
during prophase
I.Homologous chromosome are held together by
proteins in the synaptonemalcomplex.
Synaptonemal complex
Second homolog
3. Crossing over,
during
prophase I.Complex of proteins forms where
crossing over will occur. Chromosomesegments
are swapped betweennon-sister chromatids.
Non-sister chromatids
Protein complex
L
Crossing over usually occurs at least once in
each non-sister chromatid, but is only shown on
1 pair here
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Figure 12-5
MITOSIS
MEIOSIS
Diploid parent cell
Diploid parent cell
Chromosome replication
Chromosome replication
Prophase I
Prophase
Tetrads form by thesynapsis of
homologouschromosomes.Crossing over occurs.
Nuclear envelope breaks down chromosomes
condense.
Metaphase I
Metaphase
Homologous pairsalign at the metaphase plate.
Individual chromosomesalign at the metaphase
plate.
Anaphase and Telophase
Sister chromatids separate nuclear envelope
re-forms.
Anaphase I and Telophase I
Homologous chromosomesseparate two haploid
cells result.
Meiosis II
Two diploid daughter cells of mitosis
Sister chromatidsseparate.
Four haploid daughter cells of meiosis
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Figure 12-9
Example individual who is heterozygous at two
genes
Maternal chromosome
Paternal chromosome
Maternal chromosome
Paternal chromosome
Allele that contributes to black hair
Allele that contributes to red hair
Allele that contributes to brown eyes
Allele that contributes to green eyes
Hair color gene
How many pairs of chromosomes does this organism
have?
Eye color gene
During meiosis I, tetrads can line up two
different ways before the homologs separate.
OR
Brown eyes Black hair
Green eyes Black hair
Green eyes Red hair
Brown eyes Red hair
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Figure 12-9
Example individual who is heterozygous at two
genes
Maternal chromosome
Paternal chromosome
Maternal chromosome
Paternal chromosome
Allele that contributes to black hair
Allele that contributes to red hair
Allele that contributes to brown eyes
Allele that contributes to green eyes
Hair color gene
Thus you could say that meiosis is an engine
for variability it tends to throw lots of forms
into the environment in every breeding cycle...
Though it DOES NOT MAKE the variations!
Eye color gene
During meiosis I, tetrads can line up two
different ways before the homologs separate.
OR
Brown eyes Black hair
Green eyes Black hair
Green eyes Red hair
Brown eyes Red hair
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So how do mitosis and meiosis fit in?

• consider the biodiversity of life-cycles
• some are entirely sexual, some entirely asexual,
  some are both, and some even have something
  extra
• BUT
• in most cases, they arent capricious the forms
  and transitions observed make a lot of sense in
  the ecological context of the organism
• so how?

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Figure 29-20a
Protists introducing alternation of
generations
A life cycle dominated by haploid cells (species
shown here is the dinoflagellate Gynodinium
fuscum)
(n)
(n)
ASEXUAL REPRODUCTION (offspring produced by
mitosis)
SEXUAL REPRODUCTION (offspring produced by
meiosis)
FERTILIZATION
Mature cell (n)
MITOSIS
MEIOSIS
Zygote (2n)
Haploid
?
Diploid
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Figure 29-20b
Protists introducing alternation of
generations
A life cycle dominated by diploid cells (species
shown here is the diatom Cyclotella meneghiniana)
?
Gametes (n)
MEIOSIS
(2n)
ASEXUAL REPRODUCTION (offspring produced by
mitosis)
SEXUAL REPRODUCTION (offspring produced by
meiosis)
MITOSIS
FERTILIZATION
Mature cell (2n)
MITOSIS
Zygote (2n)
GROWTH
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Figure 29-21b
Protists introducing alternation of
generations
Alternation of generations in which multicellular
haploid and diploid forms look different (here,
Laminaria solidungula)
Spores (n)
?
MITOSIS
MEIOSIS
MITOSIS
Gametophytes (n)
Sperm
Sporophyte (2n)
Zygote (2n)
MITOSIS
Egg
FERTILIZATION
MITOSIS
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Figure 29-9
Protists slime molds the blob attacks!
Cells (n) aggregate when food is scarce
Amoebae (n) germinate from zygote
Spores (n)
Amoebae (n) germinate from spores
MITOSIS
ASEXUAL REPRODUCTION
SEXUAL REPRODUCTION
Fruiting body
?
MEIOSIS
Stalk
Migrating individual (slug) (n)
Giant cell (2n)
CELL FUSION
Two cells (n) in aggregation fuse, then consume
other cells
Be grossed out in detail by reading Box 29.2 in
Freeman.
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Figure 30-17a
Plants n/2n alternation and the challenges of
life on land
Mosses Gametophyte is large and long lived
sporophyte depends on gametophyte for nutrition.
Archegonium
Haploid (n)
Diploid (2n)
FERTILIZATION
MITOSIS
Egg (n)
Zygote (2n)
Eggs form in archegonia
Developing sporophyte (2n)
Sperm swim to egg
Mature sporophyte     (2n)
Developing sporophyte (2n)
Sperm form in antheridia
Spores (n) are produced in sporangia by meiosis,
dispersed by wind
Mature gametophyte (n)
Mature gametophyte (n)
Developing gametophyte
MITOSIS
MEIOSIS
?
Spore (n)
Moss is one end of a continuum, not very
land-adapted
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Figure 30-22
Plants n/2n alternation and the challenges of
life on land
?
MITOSIS
MEIOSIS
Microspore (n) forms pollen grain
Pollen grain (male gametophyte)
POLLINATION
Anther
Stamen
Carpel
Flower
Ovule
MITOSIS
MEIOSIS
Ovary
Egg
Female gametophyte (n retained in ovary)
Megaspore (n retained in ovary)
Megasporangium
FERTILIZATION
Mature sporophyte flower (2n)
Endosperm (3n) forms nutritive tissue in seed
Nutritive tissue
Embryo (2n)
Haploid (n)
Zygote (2n)
MITOSIS
Developing sporophyte
Diploid (2n)
Seed (disperses via wind or animals)
and flowering plants are the ultimate in
land-adaptation.
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Figure 31-13d
Fungi just a bit weird, but it still works.
Basidiomycota have reproductive structures with
many spore-producing basidia.
?
KARYOGAMY
2n
MEIOSIS
Spores (n) germinate to form hyphae
Spores (n)
Basidium
Mature spore- producing body (n n)
Hyphae of different mating types fuse
Heterokaryotic mycelium begins to grow
MITOSIS
PLASMOGAMY
This is one of many variants, but all have the
nn stage.
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Figure 12-3
Animals not all like this, but close enough.
?
MEIOSIS
In animals, meiosis occurs priorto production of
eggs and sperm
Haploid gametes (n)
Diploid adult (2n)
Egg
Sperm
MITOSIS
FERTILIZATION
Cell divisionsresponsible for growth(addition
of somatic cells)
Zygote (2n)
Much as plants have done, animals have solved
life on land by dramatically reducing the
exposure of weak parts.