History II Flashcards
Alleles
A version of a gene, controls a particular feature of an organism
Geographic Variation
separation between populations can lead to differences in the phenotypic variation
Restricted gene flow, on the other hand, can lead to abrupt differences, even speciation.
cline, can be seen as populations of a given species vary gradually across an ecological gradient
Types of natural selection
- stabilizing
middle ground - directional
extreme - diversifying
two extreme
sexual dimorphism
Differences in physical appearance between males and females
Frequency-Dependent Selection
survival of a trait depends on how common or rare it is in the population.
Traits that are less common have a higher survival advantage.
Phylogenetic Trees
rooted tree attempts to identify when various species diverged from a common ancestor while the (b) unrooted tree does no
Cladistics
sorts organisms into clades: groups of organisms that descended from a single ancestor
Maximum parsimony
The simplest explanation is usually correct when constructing evolutionary trees.
Horizontal gene transfer (HGT
Transfer of genes between unrelated species.
HGT in Prokaryotes
1.Transformation: naked DNA is taken up by a bacteria
2.Transduction: genes are transferred using a virus
3.Conjugation: the use a hollow tube called a pilus to transfer genes between organisms
4.Small, virus-like particles called gene transfer agents (GTAs) transfer random genomic segments from one species of prokaryote to another
Genome Fusion and Endosymbiont Theory
Ultimate: two species merge their DNA into one. ( genome fusion)
The Endosymbiont Theory suggests that mitochondria and chloroplasts in eukaryotic cells originated from prokaryotes
Ring of life theory
phylogenetic model, the three domains of life evolved from a pool of primitive prokaryotes
Molecular systematics works best when used ________.
in conjunction with morphologic information
The ________ system uses a hierarchical model for classification.
Linnaean
The first eukaryotic cells may have evolved due to ________.
GENOME FUSION of different prokaryotes to generate an endosymbiotic organism.
Prokaryotic HGT Mechanisms:
Prokaryotic HGT Mechanisms:
Transformation: Bacteria pick up DNA from their environment (e.g., from dead cells).
Transduction: A virus (bacteriophage) transfers genes from one bacterium to another.
Conjugation: Bacteria use a pilus (tube-like structure) to directly transfer genes to each other.
Gene Transfer Agents (GTAs): Small virus-like particles that transfer random pieces of DNA between prokaryotes.
Eukaryotic HGT Mechanisms:
Genes don’t just pass from parent to child—they can jump between different species through food, viruses, or even natural DNA movement
HGT in Prokaryotes
Prokaryotes (like bacteria) can exchange genes in several ways:
Transformation: Bacteria pick up free DNA from their environment.
Transduction: A virus carries genetic material from one bacterium to another.
Conjugation: A tube-like structure (pilus) connects two bacteria to transfer DNA directly.
Gene Transfer Agents (GTAs): Special particles in bacteria transfer random pieces of DNA to other bacteria.
Two Proposals for Endosymbiosis:
The eukaryotic nucleus could have formed from the fusion of archaeal and bacterial genomes.
Gram-negative bacteria (which have two membranes) may have resulted from the fusion of Archaea and Gram-positive bacteria.
Monophyletic vs. Polyphyletic vs. Paraphyletic:
Monophyletic: A group with a common ancestor and all its descendants.
Polyphyletic: A group of organisms without a common ancestor.
Paraphyletic: A group that includes an ancestor but not all of its descendants.
A “Fluid” Taxonomic System:
A classification system that changes as new discoveries are made.
