GENETICS Definitions Underlined are credit only

WordDefinition SpeciesGroup of interbreeding organisms whose offspring are fertile VariationDifferences that occur within a species ContinuousDifferences in species showing a range of values between two extremes e.g. human height or stem length of plants DiscontinuousDifferences in species which show distinct groups e.g. blood group, flower colour Inherited characteristic Determined by genetic information inherited from both parents e.g. fur colour or shape of seeds

WordDefinition UniformDescribes the phenotypes of offspring in a true breeding cross e.g. Roller (RR) x non roller (rr) = Rollers (Rr) Monohybrid crosses Cross between true breeding parents with different phenotypes of the same characteristic e.g. Black (BB) x brown (bb) PSymbol for parental generation F1 Symbol for first offspring F2 Symbol for second offspring 3:1 (¾ : ¼ )Ratio of phenotypes in F2 Why ratios don’t work Fertilisation is a random process

WordDefinition phenotypethe appearance of an individual e.g. red hair dominantphenotype or gene which always shows e.g. tall (TT) x dwarf (tt) = tall (Tt) recessivephenotype or gene that can be hidden e.g. grey (GG) x white (gg) = grey (Gg) true breedingproduces only one type of gametes e.g. GG, gg,TT,tt. GameteA sex cell which carries one of the two forms of a gene Doublethe number of sets of chromosomes in a body cell Singlethe number of sets of chromosomes in a gamete (sex cell)

WordDefinition Gamete formation When the reduction of the number of chromosomes occurs Fertilisationwhen chromosome numbers double – sperm and egg fuse GenePart of a chromosome – two forms of a gene control an inherited characteristic genotypethe genes an organism contains (genetic make up) e.g. Rr, TT, gg, Ff, Hh Parentthis individual contributes one of the two forms of a gene to their offspring alleles The name for the two forms of a gene

WordDefinition X and Y chromosomes that determine sex XYmale XXfemale X or YCan be found in male gamete (sperm) XAlways found in female gamete (egg)

WordDefinition Selective breedingWhen humans choose organisms to breed Selective breeding examples Increased yield / increased growth MutationChange in a chromosome e.g. Down’s syndrome ( 47) Mutation rate increased by radiation Advantage of a mutation Crop plants with extra chromosomes AmniocentesisUsed to detect chromosome characteristics before birth

Quiz Variation – differences in species Species – interbreeding organisms, can produce fertile offspring Fertile offspring- can breed Sterile offspring can not breed

Discontinuous variation – shows distinct (clear cut) groups Example – blood group, sex, tongue rolling Continuous variation – shows a range of values from one extreme to another Example shoe size, height, pulse rate, weight

Number of sets of chromosomes in a body cell two ( double) Number of sets in a sex cell One ( single) When chromosome numbers are reduced gamete formation When chromosome numbers are doubled fertilisation Gamete sex cell

Inherited characteristic - determined by genetic information inherited from both parents Example – sex, tongue rolling, blood group Phenotype – appearance of an inherited characteristic Example male/female, roller/non roller, A,B,O,AB

Dominant phenotype – always shows Example black X white black Recessive phenotype can be hidden

genotype– all the genes of an organism gene part of a chromosome alleles two forms of a gene e.g. T or t