GENETICS
Chromosomes: tiny thread-like structures in nucleus carrying hereditary materials, made of DNA w/ RNA and protein, 23 pairs in humans, 1 pairs- sex chromosomes
Gene: unit of hereditary material located on a chromosome in a linear manner, determines characteristic
Alleles or allolomorphics: alternative form of a gene occupying the same location (loci) on homologous chromosome (for height: alleles = tall / dwarf)
Homozygous: identical alleles for a particular trait, TT / tt
Heterozygous: different alleles for a particular trait, Tt
Recessive gene: an allele only expressed in the phenotype when in homologous conditions
Dominant gene: an allele, occurs in hetero and homozygous conditions: in heterozygous conditions it suppresses the recessive allele at the same locus
Phenotype: external appearance of an org, determined by genotype which is affected by environment
Genotype: genetic makeup in an individual, TT,tt or Tt
Hybrid: heterozygous individual, formed from a cross bet 2 homozygous (pureline variety) individuals, which have better traits than parents
Monohybrid inheritance: one pair of contrasting characters
Mendel's 1st law of segregation: of a pair of alleles controlling a particular characteristic, only one allele enters a gamete of an organism
Test / Back cross: finding genotype of a dominant phenotype by crossing it w/ a homozygous recessive individual of same species
Complete dominance: in heterozygous conditions dominant allele suppresses recessive allele from expressing itself
Incomplete dominance: neither allele is dominant over the other, both alleles express themselves in heterozygous condition (hybrid has a phenotype intermediate between that for the 2 homozygous conditions)
Co-dominant: multiple alleles that are all equally dominant (blood group alleles, A, B, O=recessive)

Mutation: sudden, significant, heritable change in structure of a DNA molecule (change in gene or chromosome #), causes change in phenotype > change in genotype
-spontaneous: naturally & artificial (induced): causes by mutagens (agents which cause/ speed up mutations, eg chemical: carcinogens, Formaldehyde, colchicine, mustard gas physical: radiation, heat, shock treatment, )
-gene & chromosomal

Gene mutation; small segment of a DNA molecule, gene, has changed in structure > diff phenotype > & genotype
Sickle-cell anemia: haemoglobin (Hb): iron-protein compound made from 4 polypeptide chains w/ a sequence of amino acids, mutations causes diff sequence > defective Hb which causes RBC to become sickle-shaped when O₂ shortage > reduce SA > severe anemia > physical weakness, heart & kidney failure, sickle RBC can block blood vessels > heart attack, due to recessive allele, homozygous recessive individuals (HbS HbS) die early, heterozygous (HbN HbS) appear normal, only mild anemia (40% abnormal Hb)
Advantage: can't suffer malaria, plasmodium can't invade RBC & reproduce

Chromosomal mutation; change in total # of chromosomes
Down's syndrome (Trisomy 21): during meiosis of gametes, due to non-disjunction abnormal gametes formed (n = 24 & 22, chromosomes fail to separate), n=22 fertilised > abortive- miscarriage, n=24 fertilised > Down's syndrome child (47 chromosomes), shown in autosomes = body chromosomes, 21st pair > 3 chromosomes (sex chromosomes = allosomes), believe to be due to abnormal ova, more probable in older women > 37 years old,
Characteristic facial features, short stout bodies, broad face, broad nose, wrinkles at corner of eyes, superficially resemble Mongolians, poor physical and mental growth, poor learning abilities, low IQ, susceptible to common infections, low resistance to diseases, heart diseases common

Variations: different characteristics shown in individuals of same species

Continuous	Discontinuous
controlled by a # of genes- polygenes	controlled by presence or absence of a single gene
characteristics show gradations from 1 extreme to another	haracteristics have no gradations, only distinct forms, no intermediates,
affected by external environmental factors	not usually affected by environmental factors
height, weight, skin colour	sex, blood group

Selection
-process of choosing more preferred phenotypes from a population which are physically, physiologically & behaviourlly better adapted to environment in order to survive & reproduce (org not adapted > die), depends on variations

Natural selection/ Survival of the fittest (Charles Darwin's theory- 'origin of species by natural selection')
-new species w/ variations (> better adapted) arise from pre-existing ones > new species reproduce > more variations, on going process

Artificial selection (by Man)
-plants and animals selected by selective breeding programs, producing desirable qualities for Man's needs
characteristics selected:
plants- good yield, size of fruits, edible, resistance (drought, pesticides, disease)
animals- viable, meat prod, disease resistant, silk prod(worms), milk prod(cows), egg prod(chicken)

Improving plant varieties by hybridization: after bud stage flowers are made into male or female ones (remove stamens- emasculation) > pollen grains dusted on to stigma > covered by plastic bag (prevents pollination by other pg) > best offspring collected and allowed to germinate > most preferred phenotypes chosen > crossing by hybridization... until new variety created that has phenotypes of original parent plants (sugar cane, rice, wheat, barley,...)

Improving animal varieties by artificial insemination (AI): outbreeding programs by artificial insemination between two animals w/ 2 different desired qualities > obtain better individuals > outbreeding repeated until preferred varieties obtained (inbreeding- crossing closely related individuals, outbreeding- crossing distantly related individuals)


Cell Strcuture and Organisation
Enzymes
Animal and Plant Nutrition
Transport in Plants and Transpiration
Support, Movement and Locomotion
Transport in Man
Respiration
Excretion
Homeostasis
The Eye
Nervous System
Chemical Control of Plant Growth
The Use and Abuse of Drugs
Diversity of Organisms
Nutrient cycles and Ecology
Parasitism
The Human Impact on the Environment
Reproduction in plants
Reproduction in animals

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