Chapter 24 1-Pager

Jason Bao, Sappington, AP Biology – Period 3, 3 March 2021
Chapter 24 in One Page

Speciation – the origin of new species and represents the focal point of evolutionary theory
Two types of evolution: Biological Species
Microevolution – changes in allele frequency (small) in a
population over time, usually hones in on a singular event or species
Concept
Biological Species – a population or group of
Macroevolution – broad patterns of evolutionary change above
the species level, cumulative effect of many speciation and populations whose members have the
extinction events potential to interbreed and produce viable,
fertile offspring but cannot do so with
Patterns of Speciation: Types of Speciation:
members of other species
Anagenesis (phyletic evolution) – transformation of an Allopatric speciation – gene flow is *Species = largest unit of population for gene flow*
lineage of organisms to a different state – LINEAR interrupted or reduced when a population is
divided into geographically isolated Limitations:
Cladogenesis (branching evolution) – budding or 1+ subpopulations - Cannot be applied to fossils or
species from parent species that continues to exist –
BRANCHED Separate populations evolve asexual organisms (prokaryotes)
independently through mutation, natural
- Gene flow can occur between
Reproductive isolation – existence of biological barriers selection, and genetic drift.
that impede two species from producing viable, fertile distinct species
offspring Regions with many geographic barriers
Hybrids – offspring of crosses between different species

typically have more species than regions
with fewer barriers.
Alternative Definitions to Species
(often times not fertile) Morphological species concept – species by
This genetic divergence can lead to structural features
Types of Reproductive Isolation: reproductive isolation (increases as distance
between populations increases). Recognition species concept – characteristics
Prezygotic (Block fertilization) – habitat, temporal, for successful mating
behavioral, mechanical, and gametic isolation Cohesion species concept – mechanisms for
Poszygotic (Prevents zygote development) – reduced discrete phenotypic entities
hybrid viability and fertibility, hybrid breakdown Ecological species concept – where species
live and what they do
Sympatric speciation – speciation occurs in Phylogenetic species concept – species =
geographically overlapping populations smallest group on phylogenetic tree
Polyploidy – multiple sets of chromosomes Miscellaneous Terms

(plants)
Punctuated Equilibria – periods of apparent
Autopolyploid – individual with more than statis punctuated by sudden change, contrasts
two chromosome sets, from one species
with model of gradualism/gradual change
Allopolyploid – species with multiple sets of
chromosomes derived from different species
Ex: Oats, Cotton, Potatoes, Tobacco, Wheat

Result of Isolation:
If contact is restored between two populations that have *Sympatric speciation can be driven by sexual
been isolated for too long, interbreeding is prevented as selection and result from the appearance of new
they are two separate species. ecological niches.*
Speciation rate – can be slow or rapid, range
Hybrid Zones from 4,000 years to 40 million years with an

average of 6.5 million years
Hybrid Zone – a region in which members of different
species mate and produce hybrids Point of speciation – it is usually determined
Hybrids are the result of mating between species with Reinforcement – hybrids are less fit than parent by a general consensus of scientists, but
species & rate of hybridization decreases
incomplete reproductive barriers factors like not being able to produce viable
Fusion – hybrids are as fit as parents, which
Hybrids often have reduced fitness compared with creates substantial gene flow that can lead to a offspring, living in completely different
parent species. fusion into a single species environments with no gene flow, a math
Stability – extensive gene flow from outside
3 possible outcomes: To the right  hybrid zone can overwhelm the selection for equation, and certain allele changes help
increased reproduction isolation convince scientists.

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Jason Bao, Sappington, AP Biology – Period 3, 3 March 2021

Chapter 24 in One Page

Hybrids – offspring of crosses between different species

Polyploidy – multiple sets of chromosomes Miscellaneous Terms

Ex: Oats, Cotton, Potatoes, Tobacco, Wheat

Hybrid Zones from 4,000 years to 40 million years with an

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