In depth summary notes for grade 12 biology / life sciences. These notes closely follow the IEB SAGS, and contain definitions, detailed explanations and relevant diagrams to help with understanding and learning for your grade 12 tests and exams.
- Gene: a short segment of DNA that codes for a particular protein
- Nucleotide: monomers of DNA
- DNA Replication: transmitting identical DNA to each new cell
- Base Triplets: three consecutive nitrogenous bases on the DNA strand
- Protein: a polymer with amino acids as monomers
- Protein Synthesis: process whereby proteins are manufactured in living cells
- Codon: three nitrogenous bases that code for a particular amino acid
- Anticodon: three exposed nitrogenous bases on tRNA molecule
- Stop Codons: three codons that do not code for amino acids
- Antibiotic: a medicine that inhibits the growth of or destroys microorganisms
- Auto-Immune Disease: a disease whereby the body attacks its own cells
- Mutation: a sudden, unexpected change in the genetic make up of an organism
- DNA Profiling: a scientific method of analysing samples of DNA to create a unique
profile for an individual
- Gel Electrophoresis: method using an electrical charge to separate large DNA
molecules
- Karyotype: diploid chromosomes arranged according to their size, shape and number in
homologous pairs within a somatic cell
- Autosomes: non-sex chromosomes
- Gonosomes: sex chromosomes (they determine the sex of the offspring)
- Homologous Chromosomes: chromosome pairs (one from each parent) that are similar
in length, gene position, and centromere location
- Bivalents: a pair of homologous chromosomes
- Chiasmata: the points at which chromatids cross over and breakages occur (meiosis)
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- Karyokinesis: division of nucleus of a cell
- Cytokinesis: division of cytoplasm in a cell
- Non-disjunction: the failure of one or more pairs of homologous chromosomes to
separate normally during meiosis, usually resulting in an abnormal distribution of
chromosomes in daughter cells
- Aneuploidy: one extra/less chromosome
- Trisomy 21: most common form of Down Syndrome, caused by an extra copy of
chromosome number 21
- Genetics: the study of hereditary and variation in living organisms
- Genome: the complete set of genes for a particular organism
- Locus: each gene has a specific position on a chromosome
- Alleles: alternate forms of the same gene
- Sex-linked alleles: alleles that are carried on the non-homologous part of an
X chromosome
- Homozygous: when two alleles (for a particular characteristic) on a homologous
chromosome are the same (i.e. ‘AA’ or ‘aa’)
- Heterozygous: when the two alleles on a homologous chromosome differ from each
other (i.e. ‘Aa’)
- Complete Dominance: when a characteristic is fully expressed in the heterozygous
phenotype of an organism
- Polygenic Inheritance: more than one pair of alleles coding for a specific trait
- Continuous Variation: form of polygenic inheritance whereby more alleles involved
offers greater variation
- Single Nucleotide Polymorphisms: genetic variations in a DNA sequence that occur
when a single nucleotide is substituted for another nucleotide
- Human Genome Project: this determines the DNA sequence of the entire human
genome – it uses information from DNA to develop new ways to treat, cure, or even
prevent the thousands of diseases that affect humans
- Environmental Watchdogs: non-governmental organisations (NGOs) making the
government and the public aware of problems relating to genetically modified organisms
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- Genetic Engineering: the altering of genes in an organism aimed at obtaining or
retaining a desired trait
- Selective Breeding / Artificial Selection: selectively choosing certain animals or plants
to sexually reproduce in order to develop specific phenotypic traits
- Transgenic Organisms: organisms that have altered genomes
- Gene Therapy: the transplantation of normal genes into cells in place of missing or
defective ones in order to correct genetic disorders
- Recombinant DNA: DNA that has been formed artificially by receiving components from
different organisms
- Vectors: carriers of genetic material
- Antigen: a toxin or foreign substance
- Hybrid Vigour: crossbred individuals that have better qualities than their parents
- Biotechnology: the field of study aimed at using living organisms to develop technology
and products that improve the quality of human life
- Cloning: a genetically identical organism is formed from the original
- Stem Cells: cells in the body that can differentiate into any specialised cells
- Sexual Reproduction: the production of new living organisms by combining genetic
information from two individuals of different sexes
- Asexual Reproduction: type of reproduction by which offspring arise from a single
parent, and inherit genes of that parent only; it does not involve the fusion of gametes,
and almost never changes the number of chromosomes
- Angiosperm: flowering plant
- Pollination: the transfer of ripe pollen from the male anther to the female stigma with the
help of biotic vectors
- Fertilisation (in plants): the fusion of the male and female gametes in the ovule of the
ovary to form a zygote
- Reproductive Strategies: structural, behavioural and functional (developmental)
adaptations that organisms display to increase the chances of fertilisation and survival of
the offspring
- Pheromone: chemical substances produced and released by some animals to aid in
courting a mate
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- Puberty: the process of physical and physiological changes
- Adolescence: the period of physical, physiological and phycological change
- Gonadotropin: hormones that stimulate the gonads
- Gonads: organs that produce gametes
- Gametogenesis: the process in which cells undergo meiosis to form gametes
- Spermatogenesis: formation of sperm cells in testes
- Oogenesis: formation of egg cells in the ovaries
- Spermatozoa: sperm
- Spermatogonium: a cell produced at an early stage in the formation of spermatozoa
- Spermatocyte: a cell produced at the second stage in the formation of spermatozoa,
formed from a spermatogonium and dividing by meiosis into spermatids
- Spermatid: an immature male sex cell formed from a spermatocyte
- Oogonium: an immature female reproductive cell that gives rise to primary oocytes by
mitosis
- Oocyte: a cell in an ovary that undergoes meiotic division to form an ovum
- Endocrinology: the study of ductless glands which produce hormones
- Hormone: a chemical / organic substance secreted by a ductless endocrine gland
aimed at changing or regulating components of the organism’s internal environment to
maintain homeostasis
- Negative Feedback System: a reaction that causes a decrease in function – it occurs in
response to some kind of stimulus – often it causes the output of a system to be
lessened; so, the feedback tends to stabilise the system
- Homeostasis: the ability to maintain a constant internal environment in response to
environmental changes
- Hyperactivity: over-secretion of a hormone
- Hypo-activity: under-secretion of a hormone
- Hyperglycaemia: high blood sugar levels
- Hypoglycaemia: low blood sugar levels
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