Advanced Biology Semester 2 Review: Genetics, Evolution, and Biochemistry

Meiosis creates four haploid gametes from a diploid parent cell through two sequential rounds of division: meiosis I and meiosis II.
Crossing over occurs during meiosis I, where homologous alleles are transferred between chromosomes to increase genetic variation.
Fertilization is the fusion of two haploid gametes, restoring the diploid number and creating a genetically unique zygote.

DNA and RNA carry heritable information; prokaryotes have circular chromosomes, while eukaryotes have linear chromosomes.
Nucleotides consist of a five-carbon sugar, a phosphate group, and a nitrogenous base.
Purines ( $G$ and $A$ ) have a double ring structure; Pyrimidines ( $C$ , $T$ , and $U$ ) have a single ring structure.
Base pairing rules: DNA uses $A-T$ and $C-G$ ; RNA uses $A-U$ and $C-G$ .
Nucleic acids are synthesized by adding nucleotides to the $3'$ hydroxyl end, forming a chain from $5'$ to $3'$ .

Transcription: RNA polymerase uses a DNA template to form mRNA.
Translation: Ribosomes (formed by rRNA and proteins) read mRNA codons. tRNA anti-codons bind to codons to assemble amino acids into a polypeptide chain.
The process starts at the start codon $AUG$ ( $MET$ ) and ends at a stop codon.

Gregor Mendel studied heredity using pea plants, establishing the principle of dominance.
Genotypes: Homozygous dominant ( $AA$ ), Heterozygous ( $Aa$ ), and Homozygous recessive ( $aa$ ).
Phenotype is the physical expression of the genotype.
Sex-linked traits are located on the $X$ and $Y$ chromosomes, such as colorblindness.

Mutations are random errors in DNA replication, repair, or division (mitosis/meiosis) influenced by radiation or chemicals.
Changes in chromosome number lead to conditions like triploidy (Down’s syndrome) or Turner syndrome.

Natural Selection: Organisms with favorable phenotypes are more likely to survive, reach maturation, and reproduce.
Fitness: Defined by reproductive success and adaptation to the environment.
Artificial Selection: Human-driven selective breeding for specific traits.
Speciation: Occurs when populations are reproductively isolated; includes divergent evolution (phenotypic diversification) and convergent evolution (similar features in unrelated species).

Evidence includes fossils (relative and radiometric dating), morphological homologies (vestigial structures), comparative embryology, and DNA sequences.
Phylogenetic trees and cladograms show evolutionary relationships; molecular data is generally more accurate than morphological traits for construction.

Nucleus: Organizes DNA into chromosomes.
Ribosomes: Sites of protein synthesis.
Endoplasmic Reticulum (ER): Smooth ER synthesizes lipids and detoxifies; Rough ER has ribosomes for glycoprotein secretion.
Golgi Apparatus: Modifies, sorts, and packages macromolecules into transport vesicles.
Lysosomes: Contain hydrolytic enzymes for digesting macromolecules in acidic environments.
Mitochondria: Sites of cellular respiration and $ATP$ generation.
Chloroplasts: Sites of photosynthesis in plants and algae.

Enzymes are catalytic proteins that speed up reactions by lowering the activation energy ( $E_A$ ).
Substrates bind to the enzyme's active site, forming an enzyme-substrate complex based on shape specificity.
Environmental factors like optimal temperature and $pH$ determine the enzyme's activity level.

Elements: Carbon, Hydrogen, and Oxygen are essential; Sulfur is for proteins; Phosphorus is for nucleic acids and phospholipids; Nitrogen is for proteins and nucleic acids.
Synthesis: Monomers join via dehydration synthesis to form polymers; polymers break down through hydrolysis.
Carbohydrates: Monosaccharides (Glucose) serve as monomers.
Lipids: Nonpolar and hydrophobic; saturated fatty acids have single bonds, while unsaturated have at least one double bond.
Proteins: Linear chains of amino acids joined by peptide bonds between carboxyl ( $-COOH$ ) and amine ( $-NH_2$ ) groups; structure is determined by the specific sequence of $20$ different R groups.