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What was the least common eukaryotic ancestor predominantly made by?
Mitosis
What was the relationship between Sex and Reproduction in the evolution of the LECA?
Sex =/= reproduction
What is saccharomyces cerevisiae?
Haploid single cell organism
What do haploid cells do in response to starvation?
2 haploid cells fuse to form a transient diploid cell
Clonal reproduction by mitotic cell divisions then occurs
The diploid then immediately enter meiosis and produces 4 haploid cells
What were the features of early eukaryotes?
Single Celled
Haploid
How did early eukaryotes reproduce?
Normally clonally by mitosis
Occasionally by sexual fusion of 2 haploid cells, creating a transient diploid, followed by meiosis producing 4 haploid cells
What are the features of modern higher eukaryotes
Modern higher eukaryotes (plants and animals) are multicellular, distinct soma and germline cells which are diploid,
How do modern higher eukaryotes reproduce?
Meiosis of germline stem cells creates haploid gametes, fusion of sperm and egg (or pollen and ovule) creates diploid zygote – clonal expansion of cells via mitosis creates the new organism
Is there sexual reproduction between every generation of multicellular organisms?
Yes
What must modern asexual organisms have evolved from at some point?
Earlier sexual species
What is sex based on?
Meiosis
What is the only type of cell to have sex?
Eukaryotes
What are the three main points about asexuality in eukaryotes?
Most higher eukaryotes use sexual reproduction and asexual reproduction is not common
Most higher eukaryotes that can reproduce asexually can also do so sexually
Obligate asexual reproduction is VERY uncommon
What is fission?
Division into 2 equally sized offspring
What is budding?
unequal division; smaller offspring
What is fragmentation?
Parent breaks into many small new individuals
What unique mechanism does Daphnia (water flea) undergo?
Switches from asexual to sexual in different seasons
What are dandelions obligate asexual by?
“Apoxmixis”
What is the process of dandelion asexual reproduction?
Diploid ovules develop into seeds → Seeds are wind disseminated
What is the process behind the Lesbian Whiptail Lizards
Pseudo-mating promotes ovulation.
On top: estradiol low & progesterone high; small ovary.
On bottom: estradiol high, ovary increase in size and ovulate.
What is phylogeny?
Evolutionary descent with reflected levels of genetic similarity
What is key about the members of one singular genus?
They all share a more closely related common ancestor than any member of another genus
Where is obligate asexual reproduction ONLY found within an otherwise sexual genus?
Level isolated species
What were the sexes originally?
Fusion between cells
What drives outbreeding in yeast?
Yeast has two mating types - one expressing ‘a’ proteins and the other expressing ‘alpha’ proteins
What is anisogomy?
Big gamete and small gamete
What does anisogamy prevent and promote?
Prevents ‘selfing’ and promotes outbreeding
What does the reproduction number determine?
How much a population will increase per generation
What does an R of 1 mean?
Population stays the same per generation
What does an R of 2 mean?
Population doubles per generation
What is a negative of sexual reproduction?
Biologically Costly (R number Wise)
→ Complex behavior required to find a mate
What does the single genome encode in sexual reproduction?
2 different gametes from 2 gonads
Other anatomical differences between sexes
What must the two sexes both do during evolution?
Co-evolve - compatible behaviours, anatomies etc
How does meiosis allow for genetic variation?
Independent assortment of chromosomes
crossing over between homologous chromosomes
What promotes genetic variation in a species genome?
Sexual reproduction coupled to diploidy
Why is giving up sex an evolutionary dead end?
Sex drove evolution - multicellularity, developmental complexity, mind
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