AP Biology Units 5-8 Comprehensive Review Flashcards

Meiosis and Genetics (Unit 5)

Comparison of Meiosis and Mitosis * Mitosis occurs in somatic cells and results in two genetically identical diploid ( $2n$ ) daughter cells. It involves a single round of DNA replication followed by a single nuclear division. Its primary functions are growth, tissue repair, and asexual reproduction. * Meiosis occurs in germ cells to produce gametes (sperm and eggs). It results in four genetically unique haploid ( $n$ ) daughter cells. It involves one round of DNA replication followed by two successive nuclear divisions: Meiosis I and Meiosis II. * Key Differences: Meiosis involves the pairing of homologous chromosomes (synapsis) and crossing over during Prophase I, whereas Mitosis does not. In Meiosis I, homologous pairs separate; in Mitosis and Meiosis II, sister chromatids separate.
Reduction of Chromosome Number * Meiosis reduces the chromosome count from diploid ( $2n$ ) to haploid ( $n$ ) by separating homologous chromosomes into different cells during Meiosis I. * Diagrammatic Representation: * Parent cell: Diploid ( $2n = 46$ in humans). * After Meiosis I: Two Haploid cells ( $n = 23$ ), each with duplicated chromosomes. * After Meiosis II: Four Haploid daughter cells ( $n = 23$ ), each with single-stranded chromosomes.
Homologous Chromosomes and Distribution * Homologous Chromosomes: Pairs of chromosomes (one from each parent) that carry the same genes at the same loci, though they may have different alleles. * Distribution: During Metaphase I, homologous pairs align at the metaphase plate and are distributed into separate nuclei during Anaphase I. This ensure each gamete receives one representative of every chromosome pair.
Mechanisms of Genetic Variation * Crossing Over: Occurs during Prophase I where non-sister chromatids of homologous chromosomes exchange segments of DNA. This produces recombinant chromosomes with new combinations of maternal and paternal alleles. * Independent Assortment: During Metaphase I, the orientation of homologous pairs relative to the poles is random. The number of possible combinations is $2^n$ , where $n$ is the haploid number. * Random Fertilization: Any sperm can fuse with any egg. For humans, the potential variation is $(2^{23}) \times (2^{23})$ combinations, excluding the effects of crossing over.
Nondisjunction and Chromosomal Mutations * Nondisjunction: The failure of chromosomes to separate properly during Meiosis I or II, resulting in gametes with an abnormal number of chromosomes (aneuploidy). * Disorder Examples: 1. Down Syndrome (Trisomy 21): Three copies of chromosome 21. 2. Turner Syndrome: Monosomy X ( $XO$ ), where a female has only one X chromosome. 3. Klinefelter Syndrome: $XXY$ genotype, where a male has an extra X chromosome. * Structural Mutations: Deletion (loss of segment), Duplication (repeat of segment), Inversion (reverse orientation), and Translocation (segment moves to a non-homologous chromosome).
Mendel’s Laws * Law of Segregation: Two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. * Law of Independent Assortment: Two or more genes assort independently—that is, each pair of alleles segregates independently of any other pair of alleles—during gamete formation. This applies only to genes located on different chromosomes or very far apart on the same chromosome.
Probability Laws in Genetics * Rule of Multiplication: The probability that two or more independent events will occur together is the product of their individual probabilities. $P(A \text{ and } B) = P(A) \times P(B)$ . * Rule of Addition: The probability that any one of two or more mutually exclusive events will occur is calculated by adding their individual probabilities. $P(A \text{ or } B) = P(A) + P(B)$ .
Non-Mendelian Inheritance Patterns * Incomplete Dominance: The phenotype of $F_1$ hybrids is somewhere between the phenotypes of the two parental varieties (e.g., red and white flowers producing pink). * Codominance: Two dominant alleles affect the phenotype in separate, distinguishable ways (e.g., MN blood group or tortoiseshell cats). * Multiple Alleles: Genes exist in more than two allelic forms (e.g., ABO blood groups: $I^A, I^B, i$ ). * X-Linked Inheritance: Genes located on the X chromosome. Males ( $XY$ ) are hemizygous and express recessive X-linked traits more frequently than females ( $XX$ ). * Multi-gene (Polygenic) Traits: Phenotypes are determined by the additive effect of two or more genes (e.g., skin color, height, forming a bell curve distribution). * Non-nuclear Inheritance: Traits determined by DNA in mitochondria or chloroplasts. These are typically inherited maternally because the zygote's cytoplasm comes from the egg.
Gene Linkage and Mapping * Gene Linkage: When genes are located on the same chromosome and tend to be inherited together. * Recombination Frequency: Calculated as $\frac{\text{Number of Recombinants}}{\text{Total Offspring}} \times 100$ . * Map Distance: Measured in centimorgans (cM); 1\text{ cM} = 1\text{% recombination frequency}.
Chi-Square ( $\chi^2$ ) Analysis * Formula: $\chi^2 = \sum \frac{(O - E)^2}{E}$ , where $O$ is the observed frequency and $E$ is the expected frequency. * Null Hypothesis ( $H_0$ ): There is no significant difference between observed and expected data; any difference is due to chance. * Alternative Hypothesis ( $H_A$ ): There is a significant difference; the observed data does not fit the expected Mendelian ratio. * Critical Value: If $\chi^2$ is greater than the critical value (based on degrees of freedom $df = n - 1$ at $p = 0.05$ ), the null hypothesis is rejected.
Phenotypic Plasticity * Definition: The ability of one genotype to produce more than one phenotype when exposed to different environments. * Example: Hydrangea flower color changes based on soil pH (acidic soil yields blue, alkaline yields pink).

DNA, Gene Expression, and Biotechnology (Unit 6)

DNA as Hereditary Material * DNA provides a stable, double-helical structure where information is stored in the sequence of nitrogenous bases ( $A, T, C, G$ ). Its ability to be accurately replicated (base pairing) and its universality allow it to serve as the blueprint for life.
Chromosome Structure and Plasmids * Prokaryotic Chromosomes: Typically single, circular DNA molecules located in the nucleoid region; lack histones. * Eukaryotic Chromosomes: Multiple, linear molecules associated with histone proteins, located in a membrane-bound nucleus. * Plasmids: Small, extra-chromosomal circular DNA molecules found in prokaryotes (and some eukaryotes like yeast) that can carry genes for antibiotic resistance.
DNA Replication * Model: Semiconservative replication, where each daughter DNA molecule consists of one old (template) strand and one new strand. * Directionality: DNA is synthesized in the $5' \rightarrow 3'$ direction. * Enzymes: * Helicase: Unwinds the double helix at replication forks. * Topoisomerase: Relieves overwinding strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands. * DNA Polymerase: Adds nucleotides to the $3'$ end of a growing DNA strand. * Ligase: Joins the Okazaki fragments of the lagging strand together. * Strands: The Leading Strand is synthesized continuously toward the replication fork, while the Lagging Strand is synthesized discontinuously as Okazaki Fragments away from the fork.
The Central Dogma * Biological information flows from DNA (information storage) to RNA (information carrier) to Protein (functional molecule).
RNA Types * mRNA: Carries the genetic message from DNA to the ribosome. * tRNA: Transports specific amino acids to the ribosome; contains an anticodon complementary to the mRNA codon. * rRNA: Forms the structural and catalytic components of ribosomes.
Transcription * Process: RNA Polymerase binds to the Promoter, unwinds the DNA, and builds an RNA transcript by reading the Template Strand (antisense/noncoding) in the $3' \rightarrow 5'$ direction, synthesizing the RNA in the $5' \rightarrow 3'$ direction. * Location: Occurs in the nucleus in eukaryotes and the cytoplasm in prokaryotes.
mRNA Processing (Eukaryotes) * 5' GTP Cap: Modified guanine nucleotide added to the $5'$ end to prevent degradation and assist ribosome binding. * 3' Poly-A Tail: A sequence of adenine nucleotides added to the $3'$ end to help export from the nucleus and stabilize the transcript. * RNA Splicing: Introns (noncoding regions) are removed, and Exons (coding regions) are joined together. * Alternative Splicing: Different exons from the same gene are joined, allowing one gene to code for multiple proteins.
Translation * Location: Ribosomes in the cytoplasm or on the rough ER. * Stages: 1. Initiation: Small ribosomal unit binds to mRNA and the start codon ( $AUG$ ). 2. Elongation: tRNAs bring amino acids; peptide bonds form between amino acids, growing the polypeptide chain. 3. Termination: Occurs when a stop codon reaches the A site of the ribosome, releasing the polypeptide.
Prokaryotic vs. Eukaryotic Expression * In prokaryotes, transcription and translation can occur simultaneously (coupled) in the cytoplasm. In eukaryotes, they are separated by the nuclear envelope (transcription in nucleus, translation in cytoplasm).
Retroviruses * Genetic information flows from RNA to DNA. They use Reverse Transcriptase to copy their RNA genome into DNA, which is then integrated into the host genome.
Regulation of Gene Expression * Prokaryotes: Use Operons (e.g., Lac and Trp operons). A single promoter controls multiple genes on a polycistronic mRNA. * Eukaryotes: Use Enhancers and specific Transcription Factors for fine-tuned control. mRNA is monocistronic (one gene per mRNA). * Epigenetics: Reversible modifications like DNA Methylation (turns genes off) and Histone Acetylation (opens chromatin/turns genes on).
Genetic Engineering Techniques * Gel Electrophoresis: Separates DNA fragments by size using an electric field; DNA moves toward the positive pole because it is negatively charged. * Polymerase Chain Reaction (PCR): Rapidly amplifies specific DNA sequences. * DNA Sequencing: Determines the exact order of nucleotides in a DNA molecule.

Evolution (Unit 7)

The Theory of Evolution * Evolution is the change in the genetic composition of a population over time. The Population is the smallest unit that can evolve; individuals do not evolve.
Mechanisms of Evolution * Natural Selection: Differential survival and reproduction based on phenotypic variation. Individuals with favorable traits (higher Evolutionary Fitness) leave more offspring. * Artificial Selection: Human-directed breeding for specific traits (e.g., dog breeds, crops). * Genetic Drift: Random fluctuations in allele frequencies. * Bottleneck Effect: A sudden reduction in population size due to environmental change. * Founder Effect: A few individuals become isolated from a larger population and establish a new one. * Gene Flow: The movement of alleles between populations through migration.
Convergent Evolution * Evolution of similar (analogous) features in distantly related groups when they adapt to similar environments (e.g., wings in birds vs. bats).
Hardy-Weinberg Equilibrium * A model describing a non-evolving population where frequencies remain constant. * 5 Conditions: No mutation, Random mating, No natural selection, Extremely large population size, No gene flow. * Equations: * Allele frequencies: $p + q = 1$ * Genotype frequencies: $p^2 + 2pq + q^2 = 1$ * Where $p$ is frequency of dominant allele, $q$ is recessive; $p^2$ is homozygous dominant, $2pq$ is heterozygous, $q^2$ is homozygous recessive.
Evidence of Evolution * Homologies: Structural similarities resulting from common ancestry (e.g., vertebrate forelimbs). * Vestigial Structures: Remnants of features that served a function in ancestors (e.g., pelvic bone in whales). * Biochemical: Shared DNA sequences and universal genetic code. * Molecular Data: Usually more reliable than morphology because it quantifies exact nucleotide/amino acid changes, avoiding confusion with analogous traits.
Speciation * Allopatric Speciation: Gene flow is interrupted by a geographic barrier. * Sympatric Speciation: Occurs in populations that live in the same geographic area (often via polyploidy, sexual selection, or habitat differentiation). * Reproductive Isolation: * Prezygotic: Barriers that prevent fertilization (temporal, behavioral, mechanical, gametic isolation). * Postzygotic: Barriers that prevent the hybrid zygote from developing into a fertile adult (reduced hybrid viability/fertility).
Origin of Life * Primitive Earth: Provided inorganic precursors ( $H_2, CH_4, NH_3$ ) that synthesized organic molecules (Miller-Urey experiment). * RNA World Hypothesis: Proposes that RNA was the first genetic material because it can both store information and catalyze reactions (ribozymes).

Ecology (Unit 8)

Behavioral and Physiological Mechanisms * Taxis: Automatic, oriented movement toward or away from a stimulus. * Kinesis: A change in activity or turning rate in response to a stimulus. * Photoperiodism: Physiological response to the relative lengths of night and day (e.g., flowering in plants). * Cooperative Behavior: Behaviors like pack hunting or kin selection (aiding relatives) increase the survival of shared genes, thus increasing inclusive fitness.
Energy and Metabolism * Endotherms: Use thermal energy generated by metabolism to maintain a homeostatic body temperature (e.g., mammals). * Ectotherms: Rely on external environmental sources for body heat (e.g., reptiles). * Metabolic Rate: Smaller organisms generally have a higher metabolic rate per unit body mass than larger organisms.
Energy Flow and Matter Cycling * Energy Flow: Unidirectional. Moves from autotrophs (producers) to heterotrophs (consumers). Only about $10\%$ of energy is transferred between trophic levels. * Matter Cycles: Biogeochemical cycles (Carbon, Nitrogen, Phosphorus, Hydrologic) recycle nutrients through the ecosystem.
Population Growth Dynamics * Exponential Growth: $\frac{dN}{dt} = r_{max} N$ . Occurs under ideal conditions with abundant resources. * Logistic Growth: $\frac{dN}{dt} = r_{max} N \left( \frac{K-N}{K} \right)$ . Incorporates Carrying Capacity ( $K$ ), the maximum population size an environment can support.
Life History Strategies * r-selected: High growth rate, many offspring, low parental care, unstable environments. * k-selected: Stable population near carrying capacity, few offspring, high parental care. * Survivorship Curves: * Type I: High survival in early/middle life; steep drop in old age (humans). * Type II: Constant death rate over lifespan (birds). * Type III: High death rate for young; flat for those that survive to old age (trees, fish).
Community Interactions * Symbiosis: Mutualism ( $+/+$ ), Commensalism ( $+/0$ ), Parasitism ( $+/-$ ). * Niche Partitioning: Competing species use different resources or the same resource in different ways/times to coexist. * Keystone Species: Have a disproportionately large effect on their environment relative to their abundance; their removal can cause a Trophic Cascade and ecosystem collapse.
Simpson’s Diversity Index * Formula: $D = 1 - \sum (\frac{n}{N})^2$ . Represents the probability that two individuals randomly selected from a sample will belong to different species. Higher index values indicate higher diversity and usually higher ecosystem resilience.