Phylogeny Flashcards
Forces that drive allele frequency change
Migration and gene flow
genetic drift
non-random mating
Migration and gene flow
-Movement of genes as a result of movement of populations to different regions
-Genetic differences reduced and genetic variation is increased due to interbreeding
-over time, it substantially aleter gene freqeuncy
E.Migration
B allele of ABO blood group present in a low gradient from east to west due to migration of Mongols over Europe
Genetic Drift
-Chance alone can vause fluctuations in allele frequency
-Includes Founder effect and genetic bottleneck
-Surviving alleles are random and not due to genetic advantage
Founder effect
-Small migration of people with a specific allele that populate an area to create a large population all containing same allele
-Genes carried by all memebers of pop derived fro same founders
Genetic Bottleneck
Large population undergoes drastic but temporary reduction in numbers
-Genetic diversity reduced even after pop recovers
-Usually a catastrophic event occurs
Non-random mating
Alters genotype freqeuncy (hetero vs homo) but not allele frequency
-Selection for or against certain traits has the potential to affect overall allele frequencies but does not itself directly change allele frequencies
Positive assortative mating
Similar genotypes more likely to mate than dissimilar ones
-part of non-random mating
Negative assortative mating
Dissimilar genotypes more likely to mate
Inbreeding
Mating between closely-related individuals, such as relatives
-Selects for homozygous phenotype
species
A group of actually or potentially interbreeding organisms that is reproductively isolated in nature from all other such groups
-Members are able to interbreed and produce viable offspring
Speciation
Transforms the parental species into another species or divides a single species into two or more seperate species
Speciation event requirements
Changes in morphology, physiology and adaptions to ecological niches may occur but are not neccessary for itto occur
genetic divergence
Different allele frequencies or alleles in gene pools reflective of forces such as natural selection, mutation and genetic drift
-When gene flow is absent/reduced- population can diverge to the point that members of one population are no longer able to successfully interbreed with members of the other.
Reproductive Isolating mechanisms
Prezygotic mechanisms
Postzygotic mechanisms
Prezygotic mechanisms
-Prevents fertilisation and zygote formation
-Geographic or ecological
-Seasonal or temporal
-Behavioural
-Mechanical
-Physiological
Geographic or ecological
The pop lives in the same regions but occupy different habitats
Seasonal or temporal
Pop live in the same regions but are sexually mature at different times
Behavioural
Only in Animals
The pop are isolated by different and incompatible behaviour before mating
Mechanical
Cross-fertilization is prevented or restricted by differences in reproductive structures ( genitalia in animals, flowers in plants)
Physiological
Gametes fail to survive in alien reproductive tracts
sperm cant survive in female
Postzygotic isolating mechanisms
Fertilisation takes place and hybrid zygotes are formed but these are nonviable or give rise to weak or sterile hybrids
-Hybrid nonviability or weakness
-Developmental hybrid sterility
-Segregational hybrid sterility
Developmental hybrid sterility
Hybrids are sterile because gonads develop abnormally or meiosis breaks down before completion
Segregational hybrid sterility
Hybrids are sterile because of abnormal segregation into gametes of whole chromosomes, chromosome segments, or combinations of genes
Rate of macroevolution
Average time is 100 000 to 10 000 000 years
-Rapid selection in shorter time spans observed in fish in East African laeks like marine salmon and palm trees in isolated islands
Phylogeny
-Genetic differences or similarities among present-day species used to reconstruct evolutionary histories
-Branches represent relationships among lineages over time
length if branch represents length of time between speciation events
-Branch nodes: when a species split into two or more species
-Node: common ancestor of species diverging from node
-Tips of branches: Species alive today or those that ended in extinction
Monophyletic group
Ancestral species and all of its descendants
Sources of phylogeny tree creation
Differences in the morphology of living organisms
fossils
molecular sequences of DNA
protein
RNA
NB: only one source can create on tree
Constructing of phylogeny trees from DNA
1.DNA sequences representing either a gene or genome of a large number of different species must be acquired
2.Sequences are aligned with each other so relative parts of sequence can be compared to see if they are the same or different. Software can be used to maximise the number of aligned base pairs by inserting gaps as needed. Closely related species will have fewer differences and more distantly related species would have acquired more DNA differences due to longer time elapsed.
3.DNA differences used to construct a phylogenetic tree, beginning with most closely related species and working back to those less closely related
Molecular clock
Measure rate of evolutionary change
Use rate of change of amino acid or nucleotide sequences to estimate divergence from common ancestor
can only be used if they are linear over certain time scales
Time and dates added to clock using independent evidence such as the fossil record
Origins of Human Genome
Homo sapiens arose 300 000 years ago from earlier species of Homo
sapiens migrated out of Africa between 50 000 and 70 000 years ago
Other homo species occupied parts of Europe and Asia
Genomes from Neanderthals and humans are 99.7% identical
Interbreeding of human populations
neanderthals disappeared 40 000 years ago and coexisted with humans for 30 000 years
2% of all human DNA is made of Neanderthal DNA
Almost 20% of Nenderthal genome present in non-African population
Neanderthal are not direct ancestors as we interbrd with them
Since different populations have different amounts of N DNA, it gives additional evidence that we did not evolve from them
Denisovans are another type of homo that are more closely related to sapiens than N and were found in Siberia, 44-54 thousand years ago it entered our DNA
Denisovan DNA mainly found in high quanitities in island nations like Fuji and Australians
% of Denisovan DNA
Modern humans have 5-6% DNA from Melanesian islanders, derived from Denisovans
