Importantvocabulary • TRAIT: carácter • GENE: gen • ALLELE: alelo • HOMOLOGOUS PAIRS: cromosomas homólogos • LOCUS: locus (lugar) • HOMOZYGOUS: homocigoto • HETEROZYGOUS: heterocigoto • HYBRID: híbrido • PURE-BREEDING: raza pura • DOMINANT: dominante • RECESSIVE: recesivo • GENOTYPE: genotipo • PHENOTYPE: fenotipo
Genes and genotype • A GENEis a piece of DNA thatcarries a treat and transmitsgeneticinformation. • A Genotypeisthe set of genes thatan individual has. Itisthe set of observable traits. • A gene can havedifferentvariants. Eachvariantiscalledanallele.Individualshavetwoallelesforeachtrait. • Ifbothalleles are identical: homozygous • Ifbothalleles are different: heterozygous
BEFORE SOVING A PROBLEM • Youneedtostablishthelettersyouwill use: • Upper case forDOMINANT ALLELES • Low case forRECESSIVE ALLELES • TWO LETTERS PER TRAIT (onecomingfromthemother and theotherfromthefather) • Twoidenticalletters: homozygous • Twodifferentletters: heterozygous
DOMINANCE AND CO-DOMINANCE • THE DOMINAT ALLELE isstrongerthantherecessive, that’swhyitisgoingtobepresent and togivethephenotypewhenitispresent. • Ex: • Nn and NN are goingtohavethesamephenotypewhen N isdominant. • THE CO-DOMINANT ALLELES are presenttogether. Thephenotype can beintermediate. Bothalleles are equallystrong. • Ex: NN onephenot, Nnintermediate and nnisthesecondphenotype.
Mendel • GregorMendel (1822-1884) wasthefirstonetostudythetransmission of biologicaltraits. • He used pea plantswhich are easytomanipulate, self- pollinate, thevarieties show puretraits and are easytoidentify. • He statisticallyanalysedthe data. • http://anthro.palomar.edu/mendel/mendel_1.htm
Mendel’swork • Mendelcarriedoutesperimentsusing a method: • He selectedindividuals of purebreedswhichdiffered in onlyoneortwotraits: Parentgenerationor P. • He crossedthedifferentvarieties of P toobtainthe F1 generation (Filial generation), which he calledhybrid. • Then he crossedindividualsfrom F1 byself-fertilisation and studiedthedescendants, F2 generation.
Mendel’sfirstlaw • Firstlawortheuniformity of thefirst filial generation: • Whentwopurebreedswhichdiffer in onetrait are crossed, allthehybridsformed in thefirstgeneration (F1) are identicaltoeachother and tothedominant progenitor.
Mendel`ssecondlaw • OrtheSegregation of traits in thesecond filial generation: • Thetraitsthat are together in heterozygousindividuals, segregate (separate) whenthegametes are formed and are passedindependentlytothesecondgeneration (F2).
Thepunnetsquare • A tablewhichgenetists use to show thecombinations of alleles of thegametes and theproportion of thedescendents.
Mendel’sthirdlaw • OrIndependentassortment of traits: Differenttraits are transmittedindependently of eachother, so allthepossiblecombinations can appear in thedescendants.
Variations in mendelianinheritance • Whenthe 1st lawdoesnotapply: intermediateinheritance and co-dominance. • (colors and blood-groups) • Whenthe 3rd lawdoesnotapply: • Geneticlinkage: genes that are in thesamechromosome. • Geneticrecombination: aftercrossing-over • T.H. Morgandiscoveredtherecombination in thefirstdecade of 20th century-
Thegenetics of sex • Chromosomaldetermination: XX, XY (Mammals, equinoderms and molluscs XY ismale; in birdsthemaleis XX, butterflies: themaleis XX and femaleis X.) • Environmentaldetermination: temp, humidity, pH, etc: amphibians and reptiles. • Geneticdetermination: dueto a gene withseveralalleles. • Karyotypedetermination: insects (bees): diploidisfemale and haploidismale (droids)
Sex-linkedinheritance • Thehuman sex chromosomes: X and Y havemorphologicaldifferences: Y issmaller and theyhavedifferentgeneticcontents. • Homologoussegment: wherethe genes thatgovernthesametraits are found • Differentialsegment: genes that are onlyfound in onechromosome • Female can be a carrier (portadora) of a recessivetraitwhensheisheterozygousforthetrait.
Ssex-linkedinheritance • Colourblindness and haemophilia (inability to distinguish red and green, and non coagulation of blood) are producedbyrecessive genes in X chromosome.
FamiliytreEs (pedigrees) • Familytrees are graphsthatcontainallthemembers of thefamily of manygenerations and it shows one, or more treats. • They can be used to study and followthepresence of certaintreats in thefamily. • Symbols: • Female: • Male: • Affectedpeople: