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 Figure: 11_01 Title: The relationships among genes, alleles, and chromosomes Caption: Homologues carry the same gene loci but may have the same or different alleles at corresponding loci. 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. Figure: 11_02 Title: Gregor Mendel Caption: 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.

flower dissected to show reproductive structures intact pea flower flower dissected to show reproductive structures Figure: 11_03 Title: Flowers of the edible pea Caption: In the intact pea flower (left), the lower petals form a container enclosing the reproductive structures. Pollen normally cannot enter the flower from outside, so peas usually self-fertilize. If the flower is opened (right), it can be cross-pollinated by hand. Copyright © 2006 Pearson Prentice Hall, Inc.

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) Figure: 11_UN01 Title: Mendel's Peas: F1 Generation Caption: all purple-flowered plants Copyright © 2006 Pearson Prentice Hall, Inc.

self-fertilize 3/4 purple 1/4 white First generation offspring (F1) Second generation offspring (F2) Figure: 11_UN02 Title: Mendel's Peas: F2 Generation Caption: 3/4 purple 1/4 white Copyright © 2006 Pearson Prentice Hall, Inc.

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 gametes A A A A Figure: 11_UN03 Title: Mendel's Peas: Gametes from a homozygous parent Caption: Copyright © 2006 Pearson Prentice Hall, Inc.

heterozygous parent gametes A a A a Figure: 11_UN04 Title: Mendel's Peas: Gametes from a heterozygous parent Caption: Copyright © 2006 Pearson Prentice Hall, Inc.

purple parent PP P P all P sperm and eggs white parent pp p p Figure: 11_UN05 Title: Mendel's Peas: Allele production Caption: pp p p all p sperm and eggs Copyright © 2006 Pearson Prentice Hall, Inc.

F1 offspring sperm eggs P p Pp or p P Pp Figure: 11_UN06 Title: Mendel's Peas: Heterozygote offspring from dominant and recessive parents Caption: p P Pp Copyright © 2006 Pearson Prentice Hall, Inc.

Copyright © 2006 Pearson Prentice Hall, Inc. gametes from F1 plants F2 offspring sperm eggs PP P P p Pp P Figure: 11_UN07 Title: Mendel's Peas: F1 alleles to F2 generation Caption: 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.

Copyright © 2006 Pearson Prentice Hall, Inc. Pp self-fertilize 1 — 2 1 — 2 p eggs p 1 — 2 P Figure: 11_04 Title: The Punnett square method Caption: The Punnett square method allows you to predict both genotypes and phenotypes of specific crosses. Here we use it for a cross between plants that are heterozygous for a single trait, flower color. (1) Assign letters to the different alleles. Use uppercase for dominant and lowercase for recessive. (2) Determine all the types of genetically different gametes that can be produced by the male and female parents. (3) Draw the Punnett square, with the columns labeled with the egg genotypes and the rows labeled with the sperm genotypes. (We have included the fractions of these genotypes with each label.) (4) Fill in the genotype of the offspring in each box by combining the genotype of sperm in its row with the genotype of the egg in its column. (We have placed the fractions in each box.) (5) Count the number of offspring with each genotype. (Note that Pp is the same as pP.) (6) Convert the number of offspring of each genotype to a fraction of the total number of offspring. In this example, out of four fertilizations, only one is predicted to produce the pp genotype, so 1/4 of the total number of offspring produced by this cross is predicted to be white. To determine phenotypic fractions, add the fractions of genotypes that would produce a given phenotype. For example, purple flowers are produced by ¼ PP + ¼ Pp + ¼ pP, for a total of 3/4 of the offspring. 1 — 4 1 — 4 PP Pp sperm 1 — 2 p 1 — 4 1 — 4 pP pp Copyright © 2006 Pearson Prentice Hall, Inc.

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.

Copyright © 2006 Pearson Prentice Hall, Inc. Seed shape smooth wrinkled Seed color yellow green Pod shape inflated constricted Pod color green yellow Flower color purple white Figure: 11_05 Title: Traits of pea plants that Mendel studied Caption: Flower location at leaf junctions at tips of branches Plant size tall (1.8 to 2 meters) dwarf (0.2 to 0.4 meters) 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 1 — 4 1 — 4 SY Sy sY sy 1 — 4 SY 1 — 16 1 — 16 1 — 16 1 — 16 SSYY SSYy SsYY SsYy 1 — 4 Figure: 11_06 Title: Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traits Caption: In pea seeds, yellow color (Y) is dominant to green (y) and smooth shape (S) is dominant to wrinkled (s). In this cross, both parents are heterozygous for each trait (or a single individual heterozygous for both traits self-fertilizes). There are now 16 boxes in the Punnett square. In addition to predicting all the genotypic combinations and the 9:3:3:1 overall phenotypic ratio, the Punnett square predicts 3/4 yellow seeds, 1/4 green seeds, 3/4 smooth seeds, and 1/4 wrinkled seeds, just as we would expect from crosses made of each trait separately. Sy 1 — 16 1 — 16 1 — 16 1 — 16 SSyY SSyy SsyY Ssyy sperm 1 — 4 sY 1 — 16 1 — 16 1 — 16 1 — 16 sSYY sSYy ssYY ssYy 1 — 4 sy 1 — 16 1 — 16 1 — 16 1 — 16 sSyY sSyy ssyY ssyy Copyright © 2006 Pearson Prentice Hall, Inc.

Copyright © 2006 Pearson Prentice Hall, Inc. 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 Figure: 11_07 Title: Independent assortment of alleles Caption: Chromosome movements during meiosis produce independent assortment of alleles, as shown here for two genes. Each possible combination is equally likely, producing gametes in the proportions ¼ SY, ¼ sy, and ¼ Sy. meiosis II SY sy Sy sY independent assortment produces four equally likely allele combinations during meiosis Copyright © 2006 Pearson Prentice Hall, Inc.

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 Figure: 11_UN08 Title: Pair of homologous chromosomes Caption: 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.

Copyright © 2006 Pearson Prentice Hall, Inc. Figure: 11_08 Title: Photomicrograph of human sex chromosomes Caption: Notice the small size of the Y chromosome, which carries relatively few genes. Y chromosome X chromosome Copyright © 2006 Pearson Prentice Hall, Inc.

Copyright © 2006 Pearson Prentice Hall, Inc. female parent eggs Figure: 11_09 Title: Sex determination in mammals Caption: Male offspring receive their Y chromosome from the father. Female offspring receive the father’s X chromosome (labeled Xm). Both male and female offspring receive an X chromosome (either X1 or X2) from the mother. male parent female offspring sperm 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.

Incomplete dominance = Pink flowers, a combo of Red and white. Thus heterozygous alleles are both dominant and effect equally. Phenotype + Genotype = 1:2:1 RR R´R´ F1: RR´ RR´ F2: 1 — 2 1 — 2 R eggs R´ Figure: 11_10 Title: Incomplete dominance Caption: The inheritance of flower color in snapdragons is an example of incomplete dominance. (In such cases, we use capital letters for both alleles, here R and R’) Heterozygotes (RR’) have pink flowers, whereas the homozygotes are red (RR) or white (R’R’). 1 — 2 R 1 — 4 1 — 4 RR RR´ sperm 1 — 2 R´ 1 — 4 1 — 4 RR´ R´R´ Copyright © 2006 Pearson Prentice Hall, Inc.

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 Figure: 11_T01 Title: Human Blood Group Characteristics Caption: 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.