Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Designer baby wikipedia , lookup
Genetic engineering wikipedia , lookup
Genome evolution wikipedia , lookup
Genome (book) wikipedia , lookup
DNA barcoding wikipedia , lookup
Human genetic variation wikipedia , lookup
History of genetic engineering wikipedia , lookup
Genetic drift wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Population genetics wikipedia , lookup
Processes of Evolution Chapter 18.6 and 19 Sexual Selection With sexual selection, some version of a trait gives an individual an advantage over others in attracting mates Distinct male and female phenotypes (sexual dimorphism) is one outcome of sexual selection Balanced Polymorphism Balanced polymorphism Example: Sickle cell anemia and malaria ◦ A state in which natural selection maintains two or more alleles at relatively high frequencies ◦ Occurs when environmental conditions favor heterozygotes ◦ HbA/HbS heterozygotes survive malaria more often than people who make only normal hemoglobin 18.7 Genetic Drift— The Chance Changes Genetic drift ◦ A random change in allele frequencies over time ◦ Can lead to a loss of genetic diversity, especially in small populations Genetic Drift and Population Size Bottlenecks Bottleneck ◦ A drastic reduction in population size brought about by severe pressure ◦ After a bottleneck, genetic drift is pronounced when a few individuals rebuild a population ◦ Example: Northern elephant seals – once a population of 20 – now 17,000 The Founder Effect Founder effect ◦ Genetic drift is pronounced when a few individuals start a new population Inbreeding ◦ Breeding or mating between close relatives who share a large number of alleles ◦ Example: Old Order Amish in Lancaster County, Pennsylvania (Ellis-van Creveld syndrome) 18.8 Gene Flow Gene flow ◦ Physical movement of alleles caused by individuals moving into and away from populations ◦ Tends to counter the evolutionary effects of mutation, natural selection, and genetic drift on a population 19.2 Comparing Body Form and Function Comparisons of body form and structures yields clues about evolutionary relationships Morphological divergence ◦ A body part from a common ancestor becomes modified differently in different lines of descent Homologous structures ◦ Similar body parts that reflect shared ancestry ◦ The same genes direct their development Morphological Divergence Morphological Convergence Morphological convergence ◦ Evolution of similar body parts in different lineages, not in a common ancestor Analogous structures ◦ Body parts that evolved independently in separate lineages in response to the same environmental pressure 19.3 Comparing Patterns of Development Similar patterns of embryonic development are the result of master genes that have been conserved over evolutionary time Evidence of evolutionary relationships PBS embryology clip Which Embryo? Evidence for Evolution Vestigial structures are inherited from ancestors, but have lost much or all of their original function due to different selection pressures acting on the descendant. ◦ Ex. hipbones of bottlenose dolphins In ancestors, hipbones played a role in terrestrial locomotion. As the dolphin lineage adapted to life at sea, this function was lost ◦ Why would an organism possess structures with little or no function? The presence of a vestigial structure does not affect an organism’s fitness. Natural selection would not eliminate it. Forever Young Some differences between closely related species resulted from changes in rate of development Example: Chimpanzee and human skulls ◦ Early stages are similar ◦ Human skulls undergo less differential growth; juvenile traits persist Evidence for Evolution Genetics & Molecular Biology At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent. ◦ DNA and RNA carry information from generation to generation and to direct protein synthesis ◦ Similar genes and proteins are found in many organisms Hox genes – determine the headto-tail axis in embryonic development 19.4 Comparing DNA and Proteins ◦ Cytochrome b – conserved between species – mitochondrial protein in electron transfer chain Molecular Clocks The accumulation of neutral mutations in the DNA of a lineage are like ticks of a molecular clock that increase over time DNA sequences of closely related species are more similar than those of distantly related ones DNA Sequence Comparison 18.9 Reproductive Isolation Speciation ◦ Evolutionary process by which new species form ◦ Reproductive isolating mechanisms are always part of the process Reproductive isolation ◦ The end of gene exchange between populations ◦ Beginning of speciation Reproductive Isolating Mechanisms Postzygotic Isolation Mechanisms Reduced hybrid viability Reduced hybrid fertility ◦ ligers – male lion, female tiger ◦ tigons ◦ Extra or missing genes ◦ Mules(63 chromosomes) -male donkey (62 chromosomes) female horse (64 chromosomes) ◦ Robust but sterile offspring Hybrid breakdown ◦ Lower fitness with successive generations Allopatric Speciation Allopatric speciation ◦ A physical barrier arises and ends gene flow between populations ◦ Genetic divergence results in speciation ◦ Example: llamas, vicunas, and camels Allopatric Speciation on an Isolated Archipelago Sympatric Speciation In sympatric speciation, new species form within a home range of an existing species, in the absence of a physical barrier ◦ A change in chromosome number (polyploidy) can cause instant speciation ◦ Plams – difference in soil pH, etc. Parapatric Speciation In parapatric speciation, populations in contact along a common border evolve into distinct species Hybrids in the contact zone are less fit than individuals on either side Different Speciation Models Coevolution Two species in close ecological contact act as agents of selection on each other (coevolution) ◦ Predator and prey ◦ Host and parasite ◦ Pollinator and flower Over time, the two species may come to depend on each other 19.1 Taxonomy and Cladistics Taxonomy ◦ The science of naming and classifying species We group species based on what we know about their evolutionary relationships Linnaean Classification Carolus Linneaus ranked organisms into ever more inclusive categories (taxa) ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ Species Genus Family Order Class Phylum Kingdom Domain In the Linnaean system, each species is given a unique, two-part scientific name ◦ Example: the dog rose, Rosa canina ◦ The first part is the genus name The second part is the species name Linnaean Classification Ranking Versus Grouping Rankings do not necessarily reflect evolutionary relationships (phylogeny) Cladistics determines evolutionary relationships by grouping species on the basis of shared, quantifiable features (characters) A clade is a group of species that share a set of characters Cladograms If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population would you predict would be heterozygotes? Q2 = 98/200 = .49 q = square root .49 = .7 p = .3 (p + q = 1 so p + .7 = 1) 2pq = 2 x .7 x .3 = .42 = 42%