BIOSC 0160 Study Guide - Midterm Guide: Ploidy, Satellite Dna, Helicobacter Pylori
Bio Study Guide Exam #4
1. How are species defined according to the following concepts: Species in each of these can
overlap, not exact science.
● morphological species concept: Carolus Linnaeus: classify by appearance (binomial
nomenclature), if look alike=same species, if look different=different species. Similar
appearance often does imply similar genetic code.
○ Limitations: not all species have sig characteristics to differentiate. male/female
dimorphism, and cryptic species that look alike but genetically/behaviorally
different and don’t interbreed. Immature organisms don’t look like adultes
(tadpoles/frogs) Microorganisms grouped by effect, function, behavior.
● ecological species concept: species=pop of organisms sharing same envt and exploiting
same resources. Geographically isolated populations that don’t interbreed could be
considered same species because share same resources.
○ Limitations:might use same food source but be unrelated, geographically isolated
pops that don’t shares resources could still be same species.
● biological species concept: Ernst Mayr: species=groups that actually or can potentially
interbreed and produce fertile offspring but isolated from other such groups.
○ This definition limited to one point in time and does not include asexual
organisms. Fossils can’t be classified and we don’t know if they produce fertile
offspring.
● lineage species concept: species are reproductively isolated branches on the tree of life,
includes asexually reproducing species. Allow biologists to consider species over
evolutionary time. Ancestor-descendant series of populations over time. Each species
starts with speciation event (node split), ends at extinction end or at new node.
○ Limitation: sometimes hard to tell whether a species will split or rejoin in future.
Clades are hypothetical/arbitrarily drawn.
○ Phylogenetic species concept: species=tip of clade (extinct or alive).
3. What are the isolating mechanisms that lead to speciation?
● Lineage can change without separating species. Speciation requires interruption of gene
flow within species that previously exchanged genes.
● Incompatibilities between genes/increasing genetic divergence.
● Physical barriers
● Selective pressures
● Lack of gene flow
● Mutations
● Mating preferences even if isolated groups overlap again.
● Reproductive barriers
● Speciation rates are highly variable, influential ecological and behavioral factors: diet
specialization, pollination, sexual selection, dispersal ability.
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○ Adaptive radiation/evolutionary radiation: species arrives to new envt, no
competition, rapid evolution of many new species from ancestral population
radiates to fill dif ecological niches. Evolutionary: large number of descendants.
Adaptive: different types of descendants from same ancestor.
4. Understand the different kinds of prezygotic and postzygotic isolating mechanisms.
● Prezygotic: prevent sperm and egg from meeting and forming zygote.
○ Temporal isolation: reproductive cycles of organisms at different times.
○ Habitat isolation: dif envt selects dif alleles→ dif species.
○ Behavioral isolation: dif courtship displays, females don’t select dif males.
○ Gametic isolation: even if two species come together to reproduce, games don’t
function with reproductive tract of other species, not right chem signals.
○ Mechanical isolate: mismatch size/shape reproductive organs.
● Postzygotic: zygote forms but dies or not viable/fit/reproductive later). Selects against
hybridization.
○ Zygote mortality: embryo forms but does not develop
○ Hybrid inviability: embryo forms but viability of organism is reduced.
○ Hybrid sterility: mules. Reduced fitness→ Infertile F2 gen. Dif number of
chromosomes don’t line up.
■ Hybrid vigor: hybrid initially stronger but doesn’t live long enough to
reproduce so infertile, doesn’t succeed.
5. How is zygote mortality different from hybrid sterility?
● Zygote mortality causes embryo to die
● Hybrid sterility: embryo survives but can’t reproduce.
6. What is the difference between allopatric and sympatric speciation?
● Allopatric: ancestral population becomes geographically isolated. Different homeland.
○ Dispersal: small group moves or is carried away to new place, becomes distinct
over time.
○ Vicariance: physical barrier splits a widespread population into subgroups and
isolates overt time
● Sympatric: same homeland. Speciation without geographic barrier. Adapt to use different
elements/survive diff ways in same envt.
○ Disruptive selection: initially same group, some develop preferences for certain
foods, envts, mates, etc, then shared preference group mates amongst themselves.
○ Can arise through polyploidization: cross parents w different ploidy numbers,
hybrid either sterile or self-fertilizing. Most common in plants.
■ Autopolyploidy: polyploidy arises from chromosome duplication in a
single species. Different ploidies can mate with each other but hybrids
infertile. This species has doubled its own chromosome number. Happens
frequently. The doubled on is now its own species, dif characteristics.
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■ Allopolyploids: diff species with dif # chromosomes mate, form new
species.
8. What is PRDM9?
● A gene that codes for mRNA that codes for a protein that has zinc fingers that facilitate
crossover of hotspot sequences during meiosis. In humans chromosome 5.
● Human chromosome 5, (pr domain containing 9), controls activation of mammalian
recombination hotspots. Homologs found in most mammals and metazoans. Domain:
region of gene with a unique function. Prdm: 3 dif region, some have Zinc fingers,
carboxy terminal of gene has zinc fingers (motifs important in TFs), mediate TF binding
of 13 base pair repeats. In humans, two alleles with dif numbers of zinc fingers.
9. What are the three domains of this protein?
● N-terminus: promotes protein-protein interactions, involved in repression of transcription,
expressed during meiosis.
● Central domain: a histone methyltransferase
● C-terminus: contains zinc fingers that bind to hotspot repeats in the satellite DNA and
mediate crossover during meiosis.
10. How does this PRDM9 interact with DNA?
11. PRDM9 plays an important role in meiosis by binding to satellite DNA. Why is this
protein/DNA interaction important?
● Why important that zinc fingers recognize a particular hotspot sequence? Because it
needs to recognize to mediate the crossing over.
● When two sep species mate, can form a hybrid because the chromosomes can line up, but
then hybrid infertile because the hotspots on its two chromosomes don’t line up so can’t
get cross over so no viable F2 zygote.
12. Chimpanzees have 48 chromosomes. Humans have 46 chromosomes. How did scientists
determine that our common ancestor six million years ago had 48 chromosomes?
● All other primates have 48, so we know that’s where we came from, but in humans, 2
chromosomes combined (fusion events), sequence the whole strand look for two
centromeric regions, can see it used to be two but now formed together and mutated to
function as one.
What is a cryptic species?: two species that appear morphologically identical but are
genetically/behaviorally different.
13. What is a trophic cascade?
● Series of trophic interactions within food web where change at one level affect species
abundance or composition at another level.
14. Based on your knowledge of a trophic cascade, what changes would you predict to occur as
whale populations increase?
● Fish and krill overpopulation b/c lack predation
● No poo-namis to provide N and Fe, no water mixing.
● Less plankton, more C in atmosphere, worse climate.
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Document Summary
Bio study guide exam #4: how are species defined according to the following concepts: species in each of these can overlap, not exact science. Morphological species concept: carolus linnaeus: classify by appearance (binomial nomenclature), if look alike=same species, if look different=different species. Similar appearance often does imply similar genetic code. Limitations: not all species have sig characteristics to differentiate. male/female dimorphism, and cryptic species that look alike but genetically/behaviorally different and don"t interbreed. Immature organisms don"t look like adultes (tadpoles/frogs) microorganisms grouped by effect, function, behavior. Ecological species concept: species=pop of organisms sharing same envt and exploiting same resources. Geographically isolated populations that don"t interbreed could be considered same species because share same resources. Limitations:might use same food source but be unrelated, geographically isolated pops that don"t shares resources could still be same species. Biological species concept: ernst mayr: species=groups that actually or can potentially interbreed and produce fertile offspring but isolated from other such groups.
