Bio 51 Exam 1

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Speciation

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Focal point of evolutionary theory

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microevolution

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adaptations that evolve within a population, confined to one gene pool

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macroevolution

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evolutionary change above the species level

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What do biologist look at when grouping organism

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they compare morphology, physiology, biochemistry, and DNA sequences.

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Species

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A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.

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Reproductive Isolation

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barriers that impede two species form producing viable fertile offspring

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Hybrids

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offspring of crosses between different species

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Reproductive isolation can be classified by______________________________________.

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Whether the factors act before or after fertilization

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Prezygoticbarriers

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blocks fertilization from occuring

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How do prezygoticbarriers work

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It impedes different species from attempting to mate, prevents the successful completion of mating, and hinders fertilization if mating is successful

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Prezygoticebarriers impedes species from mating how?

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Habitat isolation (within same area), Temporal isolation, Behavioral Isolation.

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Habitat Isolation

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Two species that occupy different habitats within the same area may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers such as mountain ranges.

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Temporal Isolation

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Species that breed during different times of day, different seasons or different years cannot mix their gametes

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Behavioral Isolation

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Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. Such behavioral rituals enable mate recognition--a way to identify potential mates of the same species

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Mechanical Isolation

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Mating is attempted but morphological differences prevent its successful completion.

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Gametic Isolation

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Sperm of one species may not be able to fertilize the eggs of another species.

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How does the post-zygotic prevent hybrid zygote from developing into a viable, fertile adult.

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Reduces hybrid viability and fertility and the hybrid breaks down.

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Reduced Hybrid Viability

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Genes of the different parent species may interact and impair the hybrids development

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Reduced hybrid fertility

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Even if hybrids are vigorous, they may be sterile

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Hyrbid breakdown

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Some first generation hybrids are fertile, but when they mate with another species or with either species, offspring of the next generation are feeble or sterile

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Biological Species Concept cannot be applied to

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fossils or asexual oganisms

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Biological Species Concept

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Emphasizes reproductive isolation; relies on absence of gene flow. However, some species exchange alleles, but remain distinct.

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Alternative Species Concepts

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Apply to asexual and Sexual organisms, but can be subjective

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Autopolyploid

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Individual with more than two chromosome sets, derived from one species

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Allopolyploid

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Multiple sets of chromosomes derived from different species. More common in plants than in animals

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When closely related species meet in a hybrid zone, there are three possible outcomes

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Strengthening of reproductive barriers (reinforcement). Weakening of reproductive barriers (fusion). Continued formation of hybrid individual (stability)

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Strengthening reproductive barriers

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The reinforcement of barriers occurs when hybrids are less fit than the parent species. Over time, the rate of hybridization decreases. Whereas reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species.

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Weakening reproductive barriers

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If hybrids are fit as parents, there can be substantial gene flow between species. If gene flow is great enough, the parent species can fuse into a single species. This is a concern where introduced species meet rare natives

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Continued formation of hybrids

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Extensive gene flow outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone. In cases where hybrids have increased fitness, local extinction of parent species within the hybrid zone can prevent the breakdown of reproductive barriers.

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How long does speciation take?

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Intervals between speciation event can range from 4000 years to 40000000 years, with an average of 6500000 years. Depending on the species, speciation might require he change of only 1 allele or many alleles.

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What does the Hardy Weinberg equilibrium describe

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The constant frequency of alleles in such a gene pool

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What does the Hardy weinberg principle describe

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Describes a population that is not evolving. If a population does not meet the criteria. it can be concluded that the population is evolving

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What are the conditions for Hardy Weinberg

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No mutation, Random Mating, No natural selection, Extremely large population size, No gene flow.

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Factors that alter allele frequencies (causes of evolutionary change)

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Natural Selection, Genetic Drift, Gene Flow

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Natural Selection

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Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions

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Genetic Drift

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The smaller a sample, the greater the chance of deviation from a predicted results

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Genetic Drift describes what

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How allele frequencies fluctuate unpredictable from on one generation to the next

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Special cases of Genetic Drift

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Founder Effect, Bottleneck Effect

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Bottleneck effect

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Sometimes caused by natural disasters, sometimes caused by humans. When a natural disaster disrupts the allele frequency and drastically reducing the populations size.

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Summarize genetic drift

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Significant in small populations causes allele frequencies to change at random, can lead to loss of genetic variation within populations, Can cause harmful alleles to become fixed.

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Gene flow

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Consist of the movement of alleles among populations. Alleles can be transferred through the movement of fertile individuals or gametes.

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Loci

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A specific place along the length of a chromosome where a given gene is located.

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Relative Fitness

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The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.

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Diploid Cell

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A cell containing two sets of chromosomes (2n), one set inherited from each parent.

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Disruptive Selection

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Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.

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Balancing Selection

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Natural selection that maintains two or more phenotypic forms in a population.

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Heterzygous

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Having two different alleles for a given gene.

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Heterozygote Advantadge

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Greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool.

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Homology

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Similarity in characteristics resulting from a shared ancestry.

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Homologous Chromosomes

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A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism’s father, the other from the mother. Also called homologs, or a homologous pair.

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Haploid Cell

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A cell containing only one set of chromosomes (n).

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Sexual Dimporphism

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Marked differences between the secondary sex characteristics of males and females.

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Sister Taxa

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Groups of organisms that share an immediate common ancestor and hence are each other’s closest relatives.

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Sister Chromatid

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Either of two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, two sister chromatids make up one chromosome; chromatids are eventually separated during mitosis or meiosis II.

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S Phase

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The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

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Stabilizing Selection

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Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.

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Vestigial Structure

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A structure of marginal, if any, importance to an organism. Vestigial structures are historical remnants of structures that had important functions in ancestors.

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Centriole

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A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome has a pair of centrioles.

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Class

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In classification, the taxonomic category above the level of order.

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Community

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All the organisms that inhabit a particular area; an assemblage of populations of different species living close enough together for potential interaction.

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Convergent Evolution

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The evolution of similar features in independent evolutionary lineages.