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Summary:(U4) -genetic terms Homework: -read p. -do p. GENETICS Genetics is the study of hereditary information with respect to its coding and method of transmission from one generation to the next Gene: a unit of hereditary information -a gene is now known as pieces of DNA responsible for production of one protein -the letter chosen to represent the gene is best if capital and small case letters are easily distinguished Allele: alternate form of the same gene e.g. the gene for hair colour has brown and blonde alleles Dominant: when two different alleles are present the one that is expressed is dominant e.g. brown is dominant to blonde, indicated with capital letter (B) -dominant alleles are not always the most common trait Recessive: when two different alleles are present the one that is not expressed is recessive e.g. blonde is recessive to brown, indicated with a lower case letter (b) Homozygous: when an organism has two identical alleles for one gene e.g. BB (dominant) or bb (recessive) Heterozygous: when an organism has two different alleles for one gene e.g. Bb (the dominant trait is expressed) Genotype: the symbolic representation of the alleles for the trait e.g. BB, Bb, bb Phenotype: the physical result of the genotype e.g. Brown, Blonde Gametes: cells resulting from meiosis and are haploid (one set of chromosomes) e.g. sperm and egg Somatic cells: regular body cells and are diploid (two sets of chromosomes) Zygote: fertilized egg, diploid because it is formed by the fusion of two haploid cells Progeny: another term for offspring Diploid Number: a double set of chromosomes (normal number found in somatic cells) e.g. humans 2n# = 46, chimps 2n# = 48, fruit fly 2n# = 8 Haploid Number: a single set of chromosomes (normal number found in gametes) e.g. humans 1n# = 23, chimps 1n# = 24, fruit fly 1n#=4 Monohybrid Cross: a mating looking at one gene and two alleles e.g. BB X bb uses the gene for hair colour, alleles are brown and blonde Dihybrid Cross: a mating looking at two genes and four alleles e.g. BBRR X bbrr uses the genes for hair colour and eye colour, alleles are brown/blonde hair, brown/blue eyes Parental (P) Cross: a mating of any two parents First Filial (F1)Generation: offspring of P cross F1 cross: mating of first filial generation (not done in humans too often...generally frowned upon because the danger of two rare deleterious recessives combining is high in siblings) Second Filial (F2) Generation: progeny of F1 cross Summary:(U1) -describe Mendel’s work - monohybrid crosses Homework: -read p. GREGOR MENDEL Gregor Mendel was the first to study genetics scientifically -he was a monk who worked with peas in the mid 1800’s Why work with peas? -can be self pollinated, easy to control parental crosses (p. 155, fig. 6.4) -grow quickly -produce many seeds, improving statistics -have many obvious, contrasting traits (p. 156, fig. 6.5) Mendel’s experiments with peas led him to the following conclusions: 1. inheritance of traits was determined by genes...these genes are found in pairs (diploid) 2. one gene of each pair is in a gamete (haploid) 3. gametes unite randomly Mendel’s Laws: Law of Dominance: -if two different alleles are present for one gene (heterozygous), one allele will be expressed (dominant) and the other hidden (recessive) Law of Segregation: -gametes contain one gene of each pair, which segregate randomly eg. Bb will form gametes with B and b in a 1:1 ratio MONOHYBRID CROSS When genetics problems arise a certain form is used to predict offspring eg. A heterozygous (hybrid) purple flowered male pea is mated to a white flowered pea What offspring will be produced? This is a monohybrid cross, which involves one gene with two alleles determine what trait is dominant: -in a heterozygous organism, only the dominant trait is expressed -purple must be dominant give name of organism and gene studied: PEAS, flower colour write a legend showing dominant and recessive genes: Q = purple (dominant) q = white (recessive) write the phenotype of the parents: Purple male X White female write the genotype of the parents: Qq male X qq female write the gametes produced by each parent: Q q q q Place gametes around a Punnett square, find offspring: male gametes down side, female gametes along top gametes q q Q Qq Qq q qq qq Genotype ratio of F1: 1 Qq : 1 qq Phenotype ratio of F1: 1 purple : 1 white Summary:(U3,U7,D2) -describe dihybrid crosses -describe independent assortment Homework: -read p. -do DIHYBRID CROSSES Dihybrid crosses: a genetic cross studying two genes and four alleles eg. A heterozygous tall, green pea is mated with a short, heterozygous yellow female pea organism/genes: Pea: height, colour legend: B = tall (dominant) b = short (recessive) E = yellow (dominant) e = green (recessive) P phenotypes: hetero. tall, green male X P genotypes: Bbee X short, hetero. yellow female bbEe gametes formed: Be Be be be bE be bE be Punnett square: gametes bE be bE be Be BbEe Bbee BbEe Bbee Be BbEe Bbee BbEe Bbee be bbEe bbee bbEe bbee be bbEe bbee bbEe bbee g ratio of F1: 4 BbEe: 4 bbEe: 4 Bbee: 4 bbee or 1 BbEe: 1 bbEe: 1 Bbee: 1 bbee p ratio of F1: 1 Tall, Yellow: 1 Short, Yellow: 1 Tall, Green: 1 Short, Green Mendel’s law of Independent Assortment: -one gene behaves independently of another gene during gamete formation -this works if genes are on separate chromosomes chromosome (different chromosome pairs separate independently during meiosis) -this also works if the genes are far apart on the same chromosome (genes far apart have a large number of crossovers between them during prophase I of meisosis) -Mendel knew none of these reasons eg. gametes formed for BbEe are BE, Be, bE, be Cross BbEe X BbEe as practice: p ratio of F1 should be 9 Tall, Yellow: 3 Tall, Green: 3 Short, Yellow: 1 Short, Green Summary:(U7,D2) -describe hazards of inbreeding Homework: -review p. -do INBREEDING Inbreeding: -most families have deleterious (dangerous) recessive alleles hidden in their genes by dominant genes -the chance of an unrelated person having this same recessive is slim -if a person mates with a direct relative the chance of the same two deleterious recessive genes coming together (being homozygous) in their offspring is higher than with random mating -these recessive genes are expressed only when homozygous -this holds true for most species eg. dog breeding is monitored in order to prevent inbreeding (kennel clubs) Summary:(U6) -describe incomplete dominance/co-dominance Homework: -read p. -do pg. INCOMPLETE/PARTIAL DOMINANCE -when heterozygous individuals are present for certain traits, the resulting phenotype is a blend of the two alleles -neither allele is dominant over the other -two different letters are used for the same gene in this case eg. a red and a white flower are crossed to make pink flowers R = red flower A = white flower RA = pink flower Red flower RR R R gametes X X A White flower AA A A A R RA RA R RA RA g ratio: all RA flowers p ratio: all pink flowers CO-DOMINANCE -two traits are sometimes both FULLY expressed, not blended. eg. in blood there are two dominant alleles and one recessive allele I = dominant, with two alleles, IA and IB i = recessive Phenotype Genotype (blood type) A IAIA, IAi B IBIB, IBi AB IAIB O ii An AB type parent mates with an O parent AB X O IAIB X ii IA IB i i gametes i i IA IAi IAi IB IBi IBi g ratio: 1 IAi: 1 IBi p ratio: 1 A: 1 B -while blood type can disprove paternity, it cannot prove paternity -any other person with the same blood type may be responsible