Romania Clasa a XII-a Biology (genetics and human ecology)
Chapters: 2
1. Genetics
Molecular genetics · Human genetics
- Molecular Basis of Inheritance – DNA is the genetic material in most living things (some viruses use RNA). It is a double helix: two antiparallel strands of nucleotides, A pairs with T by 2 hydrogen bonds and G with C by 3. Long DNA is packed on histones into nucleosomes and then chromatin. DNA copies itself semi-conservatively (Meselson–Stahl). The central dogma says DNA → RNA → protein. Transcription makes RNA from one strand; in eukaryotes the hnRNA is capped, tailed and spliced. The genetic code is a triplet, has 64 codons (61 for amino acids, 3 stops), starts with AUG, is nearly universal and degenerate. Ribosomes translate mRNA into protein with tRNA adaptors. Genes are switched on and off; the lac operon is the classic example. The Human and Rice Genome Projects read whole genomes, and DNA fingerprinting uses repeat DNA (VNTRs) to identify people.
- Principles of Inheritance and Variation – Genes come in pairs (alleles). Each parent passes one allele of each pair to the child. Mendel showed dominance (3 : 1), segregation and independent assortment (9 : 3 : 3 : 1). Real life has twists: incomplete dominance (1 : 2 : 1), co-dominance (AB blood), multiple alleles, pleiotropy (one gene, many effects) and polygenic traits (many genes, one trait). Genes sit on chromosomes, so genes on the same chromosome are linked and are separated only by crossing over. Sex chromosomes decide sex (XX-XY in humans, ZW in birds, haplo-diploid in honeybees) and carry sex-linked genes (haemophilia, colour blindness). Mistakes in genes cause Mendelian disorders (thalassemia, sickle-cell) and mistakes in chromosome number cause Down, Turner and Klinefelter syndromes.
2. Human ecology
Human-modified ecosystems · *Human populations · Human impact and conservation
- Ecosystem: Structure, Productivity, Energy Flow and Pyramids – An ecosystem is a working unit of nature where living things (biotic) and non-living things (abiotic) interact. Plants make food at a rate called productivity: gross (GPP) minus respiration gives net (NPP = GPP − R). Dead matter is broken down in five steps: fragmentation, leaching, catabolism, humification and mineralisation. Energy enters as sunlight, flows one way through trophic levels and only about 10% passes on each time. Ecological pyramids of number, biomass and energy show this; number and biomass pyramids can be inverted, but the energy pyramid is always upright.
- Organisms and Populations: Growth and Interactions – A population is a group of the same species living in one area at one time. It has features that a single organism does not have: density, birth rate, death rate, sex ratio and age structure. N grows by births and immigration and shrinks by deaths and emigration. With unlimited food it grows fast (J-curve, dN/dt = rN); with limited food it slows and stops at the carrying capacity K (S-curve, dN/dt = rN(1 − N/K)). Different species affect each other: mutualism (+/+), competition (−/−), predation and parasitism (+/−), commensalism (+/0) and amensalism (−/0).
- Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).