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Fundamentals of Genetics Introduction to Genetics 1. GREGOR MENDEL - “Father of Genetics” • Austrian monk, teacher, scientist, gardener • Formulated basic laws of heredity in the early 1860s • Simplified problems; was meticulous with data collection; think quantitatively 2. Worked with garden peas because: • Easy to grow and had a short generation time • Could be self-pollinated 3. Chose true-breeding varieties for his experiments • Means no genetic variation for a trait • Studied 7 simple traits 4. Mendel cross-pollinated plants • • • P1 = parental generation F1 = first-generation (sons/daughters) F2 =second-generation 5. Principle of Dominance and Recessiveness • F1 plants resembled only one of the parents • F1 hybrids contained two factors for each trait • one dominant; (stronger, masks recessive); • one recessive; (seems to disappear) 6. Principle of Segregation • Organism contains two factors for each trait. • Factors segregate during formation of gametes. • Each gamete contains one factor for each trait. 7. Principle of Independent Assortment • Each trait is independent of another • Genes of one pair of traits assort independently • All combinations of genes occur in gametes STOP IN: P12 • Why did Mendel select pea plants to study? OUT: P 12 Pick any dominant and recessive trait. Complete and diagram the 3 types of . monohybrid crosses below. 1. Homozygous x Homozygous 2. Homozygous x Heterozygous . 3. Heterozygous x Heterozygous . . Chromosomes, Genes, and Genetic Crosses 1. Homologous Chromosomes contain genes (locations) for the same traits 2. Traits are controlled by alleles (alternative forms of a gene). 3. Genotype refers to the alleles an individual receives at fertilization 4. Phenotype refers to the physical appearance of the individual. 5. Homozygous dominant genotypes = two dominant alleles for a trait. (BB) 6. Homozygous recessive genotypes = possess two recessive alleles for a trait (bb) 7. Heterozygous genotypes = one of each allele for a particular trait (Bb) 8. Punnett Squares • Show probabilities of future offspring • Monohybrid crosses = crosses between individuals that involve one pair of contrasting traits. 9. Monohybrid Crosses (Examples) Ex 1: Pure Tall x Pure Short TT=Tall tt =short F1 T t t F2 T Tt Tt Tt Tt 100% Tall T t T TT Tt t Tt tt 25% pure tall 50% hybrid tall 25% pure short (Homozygous x Homozygous) (Heterozygous x Heterozygous) 10. Test Crosses • A cross of an individual of unknown genotype with an individual of known genotype • Tells if individual is heterozygous or homozygous • Very important to breeders STOP Dominance Has Degrees 1. Incomplete dominance • Offspring are intermediate between two parental phenotypes • Neither allele is completely dominant over the other • Both alleles influence phenotype • 3 phenotypes • Ex: Japanese Four o’clocks RR = red RR’ = pink R’R’ = white R R R’ RR’ R’ RR’ RR’ RR’ All Pink R R’ R RR RR’ R’ RR’ R’R’ 1 red : 2 pinks : 1 white 2. Codominance • Both alleles of a gene are expressed. • A person with AB blood has both A and B antigens on their red blood cells. • Neither allele is dominant or recessive RED WHITE ROAN • Ex: Red Coat - RR White Coat – WW White & Red Mixed – RW (“roan”) W W R R RW RW RW RW All Roan – both red and white hair R W R W RR RW RW WW 1 red : 2 roan : 1 white STOP IN: P 28 My Steps for Dihybrid Crosses • 1. Underline: What’s dominant, recessive, and the parents • 2. Genotype and phenotype possibilities • 3. Write genotypes of parents • 4. Diagram possible gametes X • 5. Do cross • 6. Answer question asked OUT: P 28 • • • • Prepare Data Table Count Kernels (C or D) PREDICT GENOTYPE of PARENTS purple and smooth are Dominant Purple Smooth Purple Wrinkled Yellow Smooth Yellow Wrinkled Dihybrid Cross Feather color = ORANGE or blue CREST or no crest A cross involving two pairs of contrasting traits • Example: Dominant Recessive Yy, YY = yellow yy = green Rr, RR = round rr = wrinkled Example cont. P1 RRYY x round, yellow (homozygous) rryy wrinkled, green (homozygous) RY RY ry RrYy RrYy ry RrYy RrYy Offspring are all heterozygous RrYy X RrYy • Law of Independent Assortment Genes for different traits are inherited independently R, r, Y, y go to sperm/egg independently of each other Can recombine in four ways: RY, Ry, rY, ry RY RY Ry rY ry Ry RRYY rY ry . 9 round,yellow : 3 round, green : 9:3:3:1 3 wrinkled, yellow : 1 wrinkled ,green RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy