Biology 1001A Exam Review: Inheritance, Evolution and Ecology

Terms in this set (30)

1. Genotype vs phenotypeGenotype is an organism's genetic makeup (its alleles); phenotype is its observable traits, which result from the genotype interacting with the environment.
2. State Mendel's law of segregation.Each organism carries two alleles for a gene, and these separate during gamete formation so each gamete receives only one allele.
3. State Mendel's law of independent assortment and when it applies.Alleles of different genes assort independently into gametes. It holds for genes on different chromosomes or far apart on the same chromosome.
4. Mini-problem: phenotypic ratio from a cross of Aa x Aa with complete dominance3 dominant : 1 recessive (genotypes 1 AA : 2 Aa : 1 aa).
5. Mini-problem: phenotypic ratio from a dihybrid cross AaBb x AaBb9 : 3 : 3 : 1, assuming complete dominance and independent assortment.
6. What is a test cross?Crossing an individual with a dominant phenotype to a homozygous recessive individual. If any offspring show the recessive phenotype, the tested individual is heterozygous.
7. Incomplete dominance vs codominanceIncomplete dominance: heterozygote shows an intermediate phenotype (red x white snapdragons give pink). Codominance: both alleles fully expressed (AB blood type).
8. Why are X-linked recessive disorders more common in males?Males have one X chromosome (hemizygous), so a single recessive allele produces the phenotype, while females need two copies.
9. How do crossing over and independent assortment create genetic variation in meiosis?Crossing over in prophase I exchanges segments between homologous chromosomes; independent assortment in metaphase I randomly orients homologous pairs, producing new allele combinations.
10. What does a recombination frequency tell you about two genes?How far apart they are on a chromosome: higher frequency means farther apart. 1% recombination = 1 map unit (centimorgan); the maximum observed is 50% (unlinked).
11. What is nondisjunction?Failure of homologous chromosomes or sister chromatids to separate properly in meiosis, producing gametes with an abnormal chromosome number (e.g. trisomy 21).
12. EpistasisWhen one gene's alleles mask or modify the expression of another gene, e.g. in Labrador coat colour, the E gene determines whether pigment from the B gene is deposited.
13. Four conditions Darwin identified for natural selectionIndividuals vary in traits, some variation is heritable, more offspring are produced than can survive, and individuals with certain traits survive and reproduce more.
14. What is evolutionary fitness?An individual's relative reproductive success: the number of offspring it contributes to the next generation compared with others in the population.
15. List the conditions for Hardy-Weinberg equilibrium.No mutation, no gene flow, very large population (no drift), random mating and no natural selection.
16. Mini-problem: 16% of a population shows a recessive phenotype. Find p and q.q^2 = 0.16, so q = 0.4 and p = 1 - 0.4 = 0.6. Heterozygote frequency 2pq = 0.48.
17. Genetic drift: bottleneck vs founder effectBoth are random changes in allele frequency in small populations. A bottleneck follows a drastic population reduction; the founder effect occurs when a few individuals start a new population.
18. Directional vs stabilizing vs disruptive selectionDirectional favours one extreme, stabilizing favours intermediate phenotypes, and disruptive favours both extremes over the middle.
19. What is sexual selection?Selection for traits that improve mating success, through competition within a sex (intrasexual) or choice by the other sex (intersexual), e.g. a peacock's tail.
20. Biological species concept and one limitationA species is a group of populations that can interbreed and produce fertile offspring in nature. It cannot be applied to asexual organisms or fossils.
21. Allopatric vs sympatric speciationAllopatric: a geographic barrier splits a population, which diverges. Sympatric: new species arise in the same area, e.g. by polyploidy in plants or habitat specialization.
22. Prezygotic vs postzygotic reproductive barriersPrezygotic barriers prevent fertilization (habitat, temporal, behavioural, mechanical, gametic isolation). Postzygotic barriers act after (hybrid inviability, sterility, breakdown).
23. Homologous vs analogous structuresHomologous structures share ancestry though function may differ (human arm, bat wing). Analogous structures have similar function from convergent evolution, not common ancestry (bird and insect wings).
24. Exponential vs logistic population growthExponential: dN/dt = rN, unlimited J-shaped growth. Logistic: dN/dt = rN(K - N)/K, growth slows as N approaches carrying capacity K, giving an S-shaped curve.
25. r-selected vs K-selected speciesr-selected: many small offspring, little parental care, rapid growth (insects, weeds). K-selected: few large offspring, high parental care, populations near carrying capacity (elephants).
26. Density-dependent vs density-independent factorsDensity-dependent factors (competition, disease, predation) have stronger effects as population density rises. Density-independent factors (weather, fire) act regardless of density.
27. Competitive exclusion principleTwo species competing for exactly the same limiting resources cannot coexist indefinitely; one will be excluded unless they partition resources (niche differentiation).
28. Mutualism vs commensalism vs parasitismMutualism: both benefit (+/+). Commensalism: one benefits, the other unaffected (+/0). Parasitism: one benefits at the other's expense (+/-).
29. What is a keystone species?A species with a disproportionately large effect on community structure relative to its abundance, e.g. sea otters controlling sea urchins and protecting kelp forests.
30. Why is only about 10% of energy transferred between trophic levels?Most energy is lost as heat from metabolism, or is not eaten or not digested, so food chains are usually limited to a few levels.