South 고등학교 2학년 Genetics of Organisms
Chapters: 3
1. Genes and genetic material
Inheritance of traits · Studying human inheritance · Polygenic inheritance · Chromosome and gene abnormalities · DNA structure and its discovery · Gene structure in prokaryotes and eukaryotes · Semi-conservative replication
- 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.
- Chromosomes, Genes, Alleles and Polygenic Inheritance – Each cell nucleus holds chromosomes made of DNA. All the DNA of an organism is its genome. A gene is a stretch of DNA at a fixed place on a chromosome; its different forms are alleles. Chromosomes come in pairs, one from each parent. Meiosis puts one chromosome of each pair into each gamete, and fertilisation restores the pairs. Some traits, like height, depend on many genes together (polygenic) and so show a smooth range. All living things use the same four-letter DNA code.
- 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.
- Gene Structure: What Is Inside a Gene? – A gene is a stretch of DNA that carries the instructions to make a functional product, usually a protein (sometimes an RNA). A typical gene has a promoter (where RNA polymerase binds and transcription starts), a coding region (the message) and a terminator (where transcription stops). The template strand is read; the coding strand has the same sequence as the mRNA (with T instead of U). In prokaryotes, genes are continuous (no introns) and related genes are often grouped in an operon under one promoter, making one polycistronic mRNA. In eukaryotes, genes are split: coding exons are separated by non-coding introns. The whole gene is copied into pre-mRNA; then introns are removed and exons joined (splicing), a cap and a poly-A tail are added, and the mature mRNA leaves the nucleus. Alternative splicing lets one gene make several proteins. The genome is all the DNA of an organism; in humans only about 1–2% codes for protein.
2. Gene expression
Transcription and translation · Genetic code · Regulation of gene expression · Cell differentiation in development · Development and gene control
- 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.
- Gene Regulation: How Cells Switch Genes On and Off – Every cell carries the same DNA but uses only some genes. Cells control mostly at transcription. In bacteria, the lac operon is a set of genes under one promoter and one operator: a repressor blocks it when there is no lactose; lactose removes the repressor and the genes are read (an inducible operon). In eukaryotes, transcription factors, enhancers and silencers control each gene, and epigenetic marks (DNA methylation, histone packing) can keep genes off without changing the DNA code. Different on/off patterns make different cell types (differentiation).
- Development: From One Cell to a Whole Body – Development (ontogenesis) is the life story of one organism. The zygote divides by cleavage into a ball of cells, the blastula. In gastrulation cells move inwards and make three germ layers: ectoderm, mesoderm and endoderm. Cells then differentiate: every cell has the same genes, but each type switches on a different set. Signals between cells (induction) and master genes such as Hox genes decide where each part forms. After birth or hatching the organism grows, develops directly or by metamorphosis, ages and can sometimes regenerate.
3. Biotechnology
History of biotechnology · Antibodies, stem cells, gene editing · Fields related to biotechnology · Living modified organisms · Ethical issues
- Biotechnology and its Applications – The tools of genetic engineering are used in medicine, farming and research. Bacteria make human insulin; yeast makes safe vaccine proteins. Stem cells can become many cell types. Gene therapy puts a correct gene into a patient's cells. GM crops like Bt cotton carry a gene for a protein that kills pests. Transgenic animals carry foreign genes to help study disease or make medicines. Because these are powerful, India controls them through GEAC, and laws guard against biopiracy and unfair patents.
- Bioethics: Deciding What Is Right in Biology and Medicine – Bioethics asks whether we should do what biology and medicine now let us do. It uses four principles: autonomy (respect choice), beneficence (do good), non-maleficence (do no harm) and justice (fairness). Human dignity means a person is never only a means to an end, so informed consent is needed. Therapeutic cloning may be allowed under strict rules; reproductive human cloning is banned in most countries. Start-of-life and end-of-life questions are weighed as benefits against risks and values.