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Chapter 11 • Genetics – the study of heredity • Patterns of Inheritance Copyright © 2006 Pearson Prentice Hall, Inc. 11.1 What Is the Physical Basis of Inheritance? • 11.1.1 Genes Are Sequences of Nucleotides at Specific Locations on Chromosomes • 11.1.2 An Organism’s Two Alleles May Be the Same or Different – Figure 11.1 The relationships among genes, alleles, and chromosomes (p. 168) Copyright © 2006 Pearson Prentice Hall, Inc. chromosome 1 from tomato pair of homologous chromosomes Copyright © 2006 Pearson Prentice Hall, Inc. 11.2 How Were the Principles of Inheritance Discovered? • Figure 11.2 Gregor Mendel (p. 168) • 1860’s • Studied pea plants – parents pass to offspring the genetically heritable traits Copyright © 2006 Pearson Prentice Hall, Inc. Copyright © 2006 Pearson Prentice Hall, Inc. 11.2 How Were the Principles of Inheritance Discovered? • 11.2.1 Doing It Right: The Secrets of Mendel’s Success – Figure 11.3 Flowers of the edible pea (p. 169) Copyright © 2006 Pearson Prentice Hall, Inc. intact pea flower Copyright © 2006 Pearson Prentice Hall, Inc. flower dissected to show reproductive structures Mendels Principles • Alternative forms of genes exist (more than 1 color option etc.) • 2 genes, 1 from each parent, determines…thus each parent contributes 1 for a (new) combination of 2 (principle of segregation) • Dominant shows up first, what you see/expressed (recessive, unseen but there, i.e. masked) Copyright © 2006 Pearson Prentice Hall, Inc. Genetics “terms” • • • • Homozygous – same allele, “pure” Heterozygous – diff. allele Allele – alternatives forms of genes Phenotype – physical characteristic (seen/expressed) • Wild Type – physical characteristic (phenotype) seen most commonly in nature • Genotype – genetic (chromosomal) make up Copyright © 2006 Pearson Prentice Hall, Inc. 11.3 How Are Single Traits Inherited? • 11_UN01 Mendel's Peas: F1 Generation (p. 169) • 11_UN02 Mendel's Peas: F2 Generation (p. 170) • In a mono-hybrid (X1) cross (only 1 characteristic differs at a time when crossed) Copyright © 2006 Pearson Prentice Hall, Inc. pollen Parental generation (P) pollen cross-fertilize true-breeding, purple-flowered plant true-breeding, white-flowered plant First-generation offspring (F1) all purple-flowered plants Copyright © 2006 Pearson Prentice Hall, Inc. First generation offspring (F1) self-fertilize Second generation offspring (F2) 3/4 purple Copyright © 2006 Pearson Prentice Hall, Inc. 1/4 white 11.3 How Are Single Traits Inherited? • 11.3.1 The Pattern of Inheritance of Single Traits Can Be Explained by the Inheritance of Alleles of a Single Gene – 11_UN03 Mendel's Peas: Gametes from a homozygous parent (p. 170) – 11_UN04 Mendel's Peas: Gametes from a heterozygous parent (p. 171) – 11_UN05 Mendel's Peas: Allele production (p. 171) – 11_UN06 Mendel's Peas: Heterozygote offspring from dominant and recessive parents (p. 171) – 11_UN07 Mendel's Peas: F1 alleles to F2 generation (p. 171) Copyright © 2006 Pearson Prentice Hall, Inc. More terms • Hybrid cross – offspring of 2 diff. varieties crossed. 1 = mono, 2= di • P1 generation= parents • F1 generation = offspring of P1 generation; next = F2 Copyright © 2006 Pearson Prentice Hall, Inc. homozygous parent A A Copyright © 2006 Pearson Prentice Hall, Inc. gametes A A heterozygous parent A a Copyright © 2006 Pearson Prentice Hall, Inc. gametes A a purple parent P PP P all P sperm and eggs white parent pp p p all p sperm and eggs Copyright © 2006 Pearson Prentice Hall, Inc. F1 offspring sperm eggs P p Pp P Pp or p Copyright © 2006 Pearson Prentice Hall, Inc. gametes from F1 plants F2 offspring sperm eggs P P PP P p Pp p P Pp p p pp Copyright © 2006 Pearson Prentice Hall, Inc. 11.3 How Are Single Traits Inherited? • 11.3.2 Simple “Genetic Bookkeeping” Can Predict Genotypes and Phenotypes of Offspring – Figure 11.4 The Punnett square method (p. 172) Copyright © 2006 Pearson Prentice Hall, Inc. Pp self-fertilize p 1 — 2 1 — eggs 1 — p 2 P 2 1 — PP 4 1 — 1 — Pp 4 p 2 1 — 4 pP Copyright © 2006 Pearson Prentice Hall, Inc. 1 — 4 pp 2 results w/ a monohybrid cross • 3:1 ratio phenotype • 1:2:1 ratio genotype • Look the same! Copyright © 2006 Pearson Prentice Hall, Inc. 11.3 How Are Single Traits Inherited? • 11.3.3 Mendel’s Hypothesis Can Predict the Outcome of New Types of Single-Trait Crosses Copyright © 2006 Pearson Prentice Hall, Inc. Seed shape Seed color smooth wrinkled yellow green inflated constricted green yellow purple white at leaf junctions at tips of branches tall (1.8 to 2 meters) dwarf (0.2 to 0.4 meters) Pod shape Pod color Flower color Flower location Plant size Copyright © 2006 Pearson Prentice Hall, Inc. 11.4 How Are Multiple Traits Inherited? • 11.4.1 Mendel Concluded That Multiple Traits Are Inherited Independently – Figure 11.6 Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traits (p. 173) – Figure 11.7 Independent assortment of alleles (p. 174) Copyright © 2006 Pearson Prentice Hall, Inc. What if 2 characteristics are different? • Di-hybrid cross • 2 characteristics differ simultaneously… • You get independent assortment – separate out individually during gamete formation, do not effect each other • Result: 9:3:3:1 genotype Copyright © 2006 Pearson Prentice Hall, Inc. SsYy self-fertilize eggs 1 — 4 1 — 4 SY 1 — 4 Sy 1 — 4 sY 1 — 4 sy Copyright © 2006 SY 1 — 4 Sy 1 — 4 sY 1 — 4 sy 1 — 16 SSYY 1 — 16 SSYy 1 — 16 SsYY 1 — 16 SsYy 1 — 16 SSyY 1 — 16 SSyy 1 — 16 SsyY 1 — 16 Ssyy 1 — 16 sSYY 1 — 16 sSYy 1 — 16 ssYY 1 — 16 ssYy 1 — sSyy Hall,16 Inc. 1 — 16 ssyY 1 — 16 ssyy 1 — sSyY 16 Prentice Pearson pairs of alleles on homologous chromosomes in diploid cells chromosomes replicate replicate homologous pair during metaphase of meiosis I, orienting like this or like this meiosis I meiosis II SY sy Sy independent assortment produces four equally likely allele combinations during meiosis Copyright © 2006 Pearson Prentice Hall, Inc. sY 11.5 How Are Genes Located on the Same Chromosome Inherited? • 11.5.1 Genes on the Same Chromosome Tend to Be Inherited Together – 11_UN08 Pair of homologous chromosomes (p. 175) Copyright © 2006 Pearson Prentice Hall, Inc. flower color gene pollen shape gene purple allele, P long allele, L red allele, p round allele, I Copyright © 2006 Pearson Prentice Hall, Inc. 11.5 How Are Genes Located on the Same Chromosome Inherited? • 11.5.2 Crossing Over Can Create New Combinations of Linked Alleles Copyright © 2006 Pearson Prentice Hall, Inc. 11.6 How Is Sex Determined? • Figure 11.8 Photomicrograph of human sex chromosomes (p. 175) • Figure 11.9 Sex determination in mammals (p. 176) Copyright © 2006 Pearson Prentice Hall, Inc. Y chromosome X chromosome Copyright © 2006 Pearson Prentice Hall, Inc. female parent eggs male parent female offspring male offspring Copyright © 2006 Pearson Prentice Hall, Inc. 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits? • No! • Incomplete Dominance Produces Intermediate Phenotypes – Figure 11.10 Incomplete dominance (p. 177) Copyright © 2006 Pearson Prentice Hall, Inc. P: Incomplete dominance = Pink flowers, a combo of Red and white. F1: Thus heterozygous alleles are both dominant and effect equally. Phenotype + Genotype = F2: 1:2:1 1 — 2 1 — RR R´R´ RR´ RR´ R 2 1 R´ 2 RR 4 1 1 — R — — eggs 1 — RR´ 4 R´ 2 1 — 4 RR´ Copyright © 2006 Pearson Prentice Hall, Inc. 1 — 4 R´R´ 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits? • 11.8.2 A Single Gene May Have Multiple Alleles – Figure E11.1 Cystic fibrosis (p. 179) – Table 11.1 Human Blood Group Characteristics (p. 178) Copyright © 2006 Pearson Prentice Hall, Inc. 2 alleles effect 1 trait – codominance, both phenotypes expresseed In heterozygous cross Copyright © 2006 Pearson Prentice Hall, Inc. 11.8 Do the Mendelian Rules of Inheritance Apply to All Traits? • Other exceptions… • 11.8.5 The Environment Influences the Expression of Genes – Figure 11.11 Environmental influence on phenotype (p. 178) – NATURE vs. NURTURE debates Copyright © 2006 Pearson Prentice Hall, Inc. Others… • Pleiotropy – 1 gene effects lots of characteristics (sickle cell anemia) • Polygenic inheritance – additive effect of 2+ genes = continuum, skin color • Sex linked genes – (law of independent assortment is not ALWAYS the case) i.e. color blindness example (men) • What can we do – amniocentisis, pedigree charts… Copyright © 2006 Pearson Prentice Hall, Inc.