BIOL 1200 Study Guide: Exam 2 Chap. 21 Define balancing selection. What are the two forms of balancing selection we discussed in class? Give an example of each. ∙ Heterozygote Advantage- Cases where no single allele is strongly favored, rather a balance is achieved among several alleles. If individuals who are heterozygous at a If you want to learn more check out umd mud
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certain locus have greater fitness than do both kind of homozygotes, they exhibit heterozygote advantage. o Ex: An example of heterozygote advantage occurs at the locus in humans that codes for the B polypeptide subunit of hemoglobin, the oxygen-carrying protein of red blood cells. ∙ Frequency Dependent Selection- the fitness of a phenotype depends on how common it is in the population. o Ex: African scale eating fish. Their mouth opens on one side and they will swim by a fish and quickly eat a scale and swim off. There are right-mouthed fish and left-mouthed fish. One phenotype is in favor at a time (such as right or left mouthed) and when it becomes more common it becomes less out of favor and then the other phenotype becomes more common and they switch back and forth therefore balancing the selection. Review Fig. 21.15—Make Connections in your text. ∙ Due to a point mutation, the sickle-cell allele differs from the wild-type allele by a single nucleotide. What is sexual selection? Who first recognized/proposed it? ∙ Sexual selection is the favoring of traits that increase an individual’s ability to obtain or preferentially choose mates. Charles Darwin was the first to recognize/propose it. List the fundamental asymmetries of sex. ∙ Females- Invert substantially in egg production, Produce fewer gametes over lifetime than males, ∙ Males- produce for more gametes over lifetime than females, potentially produce many more offspring than females Define intrasexual selection; intersexual selection. ∙ Intrasexual Selection- Selection within the same sex, individuals of one sex compete directly for mates of the opposite sex. Males usually compete for sexual selection; the females typically choose the mates. For example, a single male may patrol a group of females and prevent other males from mating with them. Intrasexual selection also occurs among females in a variety of species, including broad-nosed pipefish and ring-tailed lemurs. ∙ Intersexual Selection- also known as mate choice, individuals of one sex (usually the females) are choosy in selecting their mates from the other sex. In many cases the females choices depends on the showiness of the males appearance or behavior. What is female choice? Does it represent intra- or intersexual selection? ∙ The hypothesis for female choice is called the good genes hypothesis and it is that females prefer male traits that are correlated with “good genes”. If the trait preferred by females in indicative of a male’s overall genetic quality, both the male trait and the female preference in it will increase in quality. It represents intersexual selection. Why are males often brightly colored?∙ Because females prefer the brightly colored males and even though it may lead to higher predation it has a higher reproduction rate because more females choose to mate Is there empirical evidence for the good genes hypothesis? ∙ Yes, scientists looked at tadpole performance for the long-calling tadpoles which females preferred and short-calling tadpoles. The long-calling tadpoles had a higher growth rate, a quicker time to metamorphis, a larger mass at metamorphis, more tadpole survival, and higher froglet growth. The test proved that the long-calling males have better genes and are healthier. What is male-male competition? Does it represent intra- or intersexual selection? ∙ Male-male competition is when two males compete for female choice in order to control a female or even a group of females and who they can and cannot mate with. Such as the elephant seals, they fight to see who will become “beach master” or will have the beach front quality and will provide all of the reproduction for all of the female seals. This is an example of intrasexual selection. What are the consequences of sexual selection? ∙ It can cause sexual dimorphism Define sexual dimorphism. Is their connection between sexual selection and sexual dimorphism? ∙ It occurs when physical variations are found between male and female members of the same species. Yes, most of the time it is the result of sexual selection. Chap. 22 What happens when populations become genetically isolated from one another ∙ When population become genetically isolated, they evolve independently of one another which leads to speciation. Define speciation. ∙ The process by which one species split into two or more species. Species concepts definitions for: 1) Biological Species Concept (BSC) ∙ Actual interbreeding populations and potentially interbreeding populations that are reproductively isolated from other such groups. Inability of individuals from such two groups to either mate, or, reproduce with one another. It is based on the ability to reproduce, not similarity in appearance. What is a species under the BSC? ∙ The Eastern Meadowlark (Sturnella Magna) and the Western Meadowlark (Sturnella Neglecta) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild. Distinguish between prezygotic vs. postzygotic barriers that enforce reproductive isolation, starting with a definition of the word zygote. ∙ Zygote When one of the father’s sperm cells are able to penetrate the egg cell of the mother, a zygote is formed. A zygote is a diploid cell containing half of the mother’s genetic information and half of the father’s genetic information, they combine their genetic information, giving the new single cell zygote a complete set of chromosomes.∙ Prezygotic barriers they are “before the zygote” and block fertilization from occurring. Such barriers typically act in one of three ways: by impending mebers of different species from attempting to mate, by preventing an attempted mating from being completed successfully, or by hindering fertilization if mating is completed successfully. ∙ Postzygotic barriers If a sperm cell of one species overcomes prezygotic barriers and fertilizes an ovum from another species a variety of postzygotic barriers (“after the zygote”) may contribute to reproductive isolation after the hybrid zygote is formed. For example, developmental errors ay reduce survival among hybrid embryos. Or problems after birth may cause hybrids to be infertile or decrease their chance of surviving long enough to reproduce. An example of this is a mule, the hybrid offspring of a male donkey and a female horse, it is robust but sterile, meaning it cannot reproduce. Know and be able to recognize all of the prezygotic & postzygotic barriers ∙ Prezygotic Barriers o Habitat Isolation- 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. ∙ Ex: Rhagoletis fly- they occur in the same geographic areas, but the apple maggot fly (Rhagoletis Pomonella) feeds and mates on hawthorns and apples while its close relative, the blueberry maggot fly (Rhagoletis Mendax), mates and lays its eggs only on blueberries. Or the Carolina Jessamine (uplands) and the swamp Jessamine (wetlands) o Temporal Isolation- Species that breed during different times of the day, different seasons, or different years cannot mix their gametes. ∙ Ex: The orange daylily (7am to 6pm) and the citron daylily (6pm to 6am) o Behavioral Isolation- 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. ∙ Ex: The Green Anole the male with the extended dewlap. Each species has its own colored dewlap. Each female is attracted to its own species dewlap color, which keeps them from interbreeding. Another example is the bluefooted boobies, they are inhabitants of the Galapagos, mate only after a courtship display unique to their species. Part of the script calls the male to high step, a behavior that calls the female’s attention to his bright colored blue feet. o Mechanical Isolation- Mating is attempted, but morphological differences prevent its successful completion. ∙ Ex: Spiders don’t have penises; they have pedipalps which are specialized arms to transfer their sperm. It is a lock and key concept so only certain pedipalps fit in certain female spiders. o Gametic Isolation- Sperm of one species may not be able to fertilize the eggs of another species. For instance, sperm may not be able to survive in the reproductive tract of females of the other species, or biochemical mechanisms may prevent the sperm from penetrating the membrane surrounding the other species’ eggs. ∙ Ex: Sea Urchins release their sperm and eggs into the surrounding water, where they fuse and form zygotes. It is difficult for gametes of different species, such as the red and purple urchins shown here, to fuse because proteins on the surfaces of the eggs and sperm bind very poorly to each other. ∙ Post Zygotic Barriers o Reduced Hybrid Viability- the genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment. Zygote does not develop, embryos abort, hybrids often die before sexual maturity. ∙ Ex: Some salamander subspecies of the genus Ensatina live in the same regions and habitats, where they may occasionally hrybridize. But most of the hybrids do not complete development, and those that do are frail. o Reduced Hybrid Fertility- Even if hybrids are vigorous, they may be sterile. If the chromosomes of two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since the infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species. ∙ Ex: The mule, the hybrid offspring of a male donkey and a female horse, it is robust but sterile, meaning it cannot reproduce. o Hybrid Breakdown- Some first generation hybrids are viable and fertile, but when they mate with one another or with other parent species, offspring of the next generation are feeble or sterile. ∙ Ex: Strains of cultivated rice have accumulated different mutant recessive alleles at two loci in the course of their divergence from a common ancestor. Hybrids between them are vigorous and fertile, but plants in the next generation that carry too many of these recessive alleles are small and sterile. Although these rice strains are not yet considered different species, they have begun to be separated by post-zygotic barriers. Is it possible for a postmating event to qualify as a prezygotic barrier? ∙ The mule provides an example of Reduced Hybrid Fertility. What are some of the problems with the BSC ∙ There is no way to evaluate the reproductive isolation of fossils ∙ It does not apply to organisms that reproduce asexually all or most of the time, such as prokaryotes. ∙ Hybridization, such as the “Grolar Bears” 2) Morphospecies Concept ∙ Distinguishes a species by body shape and other structural features such as size. What are its advantages? Disadvantages? (Morphospecies Concept)∙ Advantages- It can be applied to asexual and sexual organisms, and it can be useful, and it can even be useful without information on the extent of gene flow. ∙ Disadvantages It relies on subjective criteria; researchers may disagree on which structural features distinguish a species. 3)Phylogenetic Species Concept (PSC) o Answer questions for Concept Check 21.1 Define cryptic species. Which species concept are they consistent with? Inconsistent with? Which species concept(s) ‘work’ with respect to fossils? Compare allopatry vs. sympatry. READ the experiment reported in Fig. 22.7: Inquiry. Are you ready to be tested on it? What do dispersal and vicariance have in common? How do they differ? Distinguish between allopatric speciation vs. sympatric speciation. Provide examples of both. Which is more rare and why? Which of the two likely involves a ‘host shift’? I really like the example of Panamanian snapping shrimp. Do you really understand it? If not, read the book!!! READ the experiment reported in Fig. 22.12: Inquiry. Are you ready to be tested on it? What is polyploidy? How does autopolyploidy differ from allopolyploidy? Consider pentaploid (5n) vs. octoploid (8n) spermatocytes undergoing meiosis. Which is more likely to produce a viable zygote? Why? Name a major taxonomic group in which polyploidy has played a significant role in speciation. Define reinforcement. What was the significance of size differences between the two Jamaican millipede species in areas of sympatry? Chap. 20 Define phylogeny, taxonomy, systematics ∙ What is a binomial species name? How is it written? Know the difference between genus name and specific epithet. Can you name the major components of a phylogenetic tree? (e.g., root, node, branch, sister group, outgroup, etc.) How are phylogenetic trees constructed? Who was the biologist who gave us the phylogenetic approach known as cladistics? Distinguish between characters and character states. What is an ancestral character state? A derived character state? How do you determine character polarity, i.e., determine whether a character state is ancestral or derived? What is a synapomorphy? Why are they important? Define the terms monophyletic, paraphyletic, polyphyletic, parsimony. How does the principle of parsimony help you to select among possible trees? READ the parsimony application in Fig. 20.15: Research Method. Are you ready to be tested on it? What are molecular clocks and why are the useful in phylogenetics? What are the three domains of life?