2Asexual ReproductionBacteria can reproduce as often as every 12 minutes – and may go through 120 generations in one dayThus capable of producing 6 x 1035 offspring per dayBacteria often produce 1 mutation per 1000 replications of DNASo for fast-growing species, mutation is a good way to respond to a changing environment
6Nonsister chromatids held together during synapsis Prophase I of meiosisNonsister chromatids held together during synapsisPair of homologsChiasmaCentromereTEMAnaphase IFigure The results of crossing over during meiosis.Anaphase IIDaughter cellsRecombinant chromosomes
7The random nature of fertilization adds to the genetic variation arising from meiosis. Any sperm can fuse with any egg.A zygote produced by a mating of a woman and man has a unique genetic identity.An ovum is one of approximately 8,388,608 possible chromosome combinations (223).The successful sperm represents one of 8,388,608 different possibilities (223).The resulting zygote is composed of 1 in 70 trillion (223 x 223) possible combinations of chromosomes.Crossing over adds even more variation to this.
9Two possible types of inheritance One possible explanation of heredity is a “blending” hypothesisThe idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make greenAn alternative to the blending model is the “particulate” hypothesis of inheritance: the gene ideaParents pass on discrete heritable units, later known as genes
10Mendel’s time TodayMendel’s garden at Brunn (Brno) Monastery
11Some genetic vocabulary Character: a heritable feature, such as flower colorTrait: a variant of a character, such as purple or white flowersGarden Pea
13Parental generation (P) TECHNIQUE12Parental generation (P)Stamens3Carpel4Figure 14.2 RESEARCH METHOD: Crossing Pea PlantsRESULTS5First filial generation offspring (F1)
14In Mendel’s Experiments: Mendel chose to trackOnly those characters that varied in an “either-or” mannerMendel also made sure thatHe started his experiments with varieties that were “true-breeding”In a typical breeding experimentMendel mated two contrasting, true-breeding varieties, a process called hybridization
15Breeding Terminology The true-breeding parents Are called the P (parental) generationThe hybrid offspring of the P generationAre called the F1 (filial) generationWhen F1 individuals self-pollinateThe F2 generation is produced
16(true-breeding parents) EXPERIMENTP Generation(true-breeding parents)Purple flowersWhite flowersFigure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
17(true-breeding parents) F1 Generation (hybrids) EXPERIMENTP Generation(true-breeding parents)Purple flowersWhite flowersF1 Generation (hybrids)All plants had purple flowersSelf- or cross-pollinationFigure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?
18(true-breeding parents) Purple flowers White flowers EXPERIMENTP Generation(true-breeding parents)Purple flowersWhite flowersF1 Generation (hybrids)All plants had purple flowersSelf- or cross-pollinationFigure 14.3 INQUIRY: When F1 hybrid pea plants self- or cross-pollinate, which traits appear in the F2 generation?F2 Generation705 purple- flowered plants224 white flowered plants
19Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
20Mendel developed a hypothesis to explain his results that consisted of four ideas Alternative versions of genes (different alleles) account for variations in inherited charactersFor each character, an organism inherits two alleles, one from each parentIf two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance. The other, recessive allele has no effect on a hybrid organism’s appearanceThe two alleles for each character segregate (separate) during gamete formation
22Law of Segregation P Generation Appearance: Purple flowers White flowersGenetic makeup:PPppGametes:PpFigure 14.5 Mendel’s law of segregation.
23Law of Segregation P Generation Appearance: Purple flowers White flowersGenetic makeup:PPppGametes:PpF1 GenerationAppearance:Purple flowersGenetic makeup:PpGametes:1/2P1/2pFigure 14.5 Mendel’s law of segregation.
24Law of Segregation P Generation Appearance: Purple flowers White flowersGenetic makeup:PPppGametes:PpF1 GenerationAppearance:Purple flowersGenetic makeup:PpGametes:1/2P1/2pSperm from F1 (Pp) plantF2 GenerationPpFigure 14.5 Mendel’s law of segregation.PEggs from F1 (Pp) plantPPPppPppp3: 1
26Test cross TECHNIQUE Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: ppPredictionsIf purple-flowered parent is PPorIf purple-flowered parent is PpSpermSpermppppPPPpPpPpPpEggsEggsFigure 14.7 RESEARCH METHOD: The TestcrossPpPpPpppppRESULTSorAll offspring purple1/2 offspring purple and 1/2 offspring white
28Hypothesis of dependent assortment EXPERIMENTYYRRP GenerationyyrrGametesYRyrF1 GenerationYyRrPredictionsHypothesis of dependent assortmentHypothesis of independent assortmentSpermPredicted offspring of F2 generationor1/4YR1/4Yr1/4yR1/4yrSperm1/2YR1/2yr1/4YRYYRRYYRrYyRRYyRr1/2YRYYRRYyRr1/4YrEggsYYRrYYrrYyRrYyrr1/2EggsFigure 14.8 INQUIRY: Do the alleles for one character assort into gametes dependently or independently of the alleles for a different character?yrYyRryyrr1/4yRYyRRYyRryyRRyyRr3/41/41/4yrPhenotypic ratio 3:1YyRrYyrryyRryyrr9/163/163/161/16Phenotypic ratio 9:3:3:1RESULTS31510810132Phenotypic ratio approximately 9:3:3:1
29Segregation of alleles into eggs Segregation of alleles into sperm RrRrSegregation of alleles into eggsSegregation of alleles into spermSperm1/2R1/2rRR1/2RRrFigure 14.9 Segregation of alleles and fertilization as chance events.1/41/4EggsrrRr1/2r1/41/4
30Probability of YYRR 1/4 (probability of YY) 1/4 (RR) 1/16 1/8Figure 14.UN01
31Probability of YYRR 1/4 (probability of YY) 1/4 (RR) 1/16 1/8Figure 14.UN01Probability of yyrr = ?A. 1/8 B. 1/16 C. 1/32
32Probability of YYRR 1/4 (probability of YY) 1/4 (RR) 1/16 1/8Figure 14.UN01Probability of YYrr = ?A. ¼ B. 1/8 C. 1/16
33Probability of YYRR 1/4 (probability of YY) 1/4 (RR) 1/16 1/8Figure 14.UN01Probability of YxRr = ?(x can be Y or y)A. ½ B. 3/4 C. 3/8 D. 1/16
341/4 (probability of pp) 1/2 (yy) 1/2 (Rr) 1/16 ppYyrr 1/4 1/2 1/2 1/16Ppyyrr1/2 1/2 1/2 2/16PPyyrr1/4 1/2 1/2 1/16ppyyrr1/4 1/2 1/2 1/16Chance of at least two recessive traitsFigure 14.UN02 6/16 or 3/8