Chapter 9 Patterns of Inheritance Power Point Lectures

Chapter 9 Patterns of Inheritance Power. Point® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc.

Biology And Society: A Matter of Breeding • Genetics is the scientific study of heredity. – Genetics explains why the offspring of purebred dogs are like their parents. – Inbreeding of dogs makes some genetic disorders common. • A dog’s behavior is determined by its – Genes – Environment © 2010 Pearson Education, Inc.

Figure 9. 00

HERITABLE VARIATION AND PATTERNS OF INHERITANCE • Heredity is the transmission of traits from one generation to the next. • Gregor Mendel – Worked in the 1860 s – Was the first person to analyze patterns of inheritance – Deduced the fundamental principles of genetics © 2010 Pearson Education, Inc.

Figure 9. 1

In an Abbey Garden • Mendel studied garden peas because they – Are easy to grow – Come in many readily distinguishable varieties – Are easily manipulated – Can self-fertilize © 2010 Pearson Education, Inc.

Petal Stamen (makes spermproducing pollen) Carpel (produces eggs) Figure 9. 2

• A character is a heritable feature that varies among individuals. • A trait is a variant of a character. • Each of the characters Mendel studied occurred in two distinct forms. © 2010 Pearson Education, Inc.

• Mendel – Created true-breeding varieties of plants – Crossed two different true-breeding varieties • Hybrids are the offspring of two different true-breeding varieties. – The parental plants are the P generation. – Their hybrid offspring are the F 1 generation. – A cross of the F 1 plants forms the F 2 generation. © 2010 Pearson Education, Inc.

Removed stamens from purple flower. White Stamens Parents (P) Carpel Purple Transferred pollen from stamens of white flower to carpel of purple flower. Figure 9. 3 -1

White Removed stamens from purple flower. Stamens Parents (P) Carpel Purple Transferred pollen from stamens of white flower to carpel of purple flower. Pollinated carpel matured into pod. Figure 9. 3 -2

White Removed stamens from purple flower. Stamens Parents (P) Carpel Purple Transferred pollen from stamens of white flower to carpel of purple flower. Pollinated carpel matured into pod. Planted seeds from pod. Offspring (F 1) Figure 9. 3 -3

Mendel’s Law of Segregation • Mendel performed many experiments. • He tracked the inheritance of characters that occur as two alternative traits. © 2010 Pearson Education, Inc.

Dominant Recessive Flower color Dominant Recessive Pod shape Purple White Flower position Inflated Constricted Pod color Green Yellow Tall Dwarf Stem length Axial Terminal Yellow Green Round Wrinkled Seed color Seed shape Figure 9. 4

Figure 9. 4

Monohybrid Crosses • A monohybrid cross is a cross between parent plants that differ in only one character. Blast Animation: Single-Trait Crosses © 2010 Pearson Education, Inc.

P Generation (true-breading parents) Purple flowers White flowers Figure 9. 5 -1

P Generation (true-breading parents) Purple flowers F 1 Generation White flowers All plants have purple flowers Figure 9. 5 -2

P Generation (true-breading parents) Purple flowers F 1 Generation White flowers All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 Generation 3 of plants 4 have purple flowers 1 of plants 4 have white flowers Figure 9. 5 -3

Figure 9. 5

• Mendel developed four hypotheses from the monohybrid cross: 1. There alternative versions of genes, called alleles. 2. For each character, an organism inherits two alleles, one from each parent. – An organism is homozygous for that gene if both alleles are identical. – An organism is heterozygous for that gene if the alleles are different. © 2010 Pearson Education, Inc.

3. If two alleles of an inherited pair differ – The allele that determines the organism’s appearance is the dominant allele – The other allele, which has no noticeable effect on the appearance, is the recessive allele © 2010 Pearson Education, Inc.

4. Gametes carry only one allele for each inherited character. – The two members of an allele pair segregate (separate) from each other during the production of gametes. – This statement is the law of segregation. © 2010 Pearson Education, Inc.

• Do Mendel’s hypotheses account for the 3: 1 ratio he observed in the F 2 generation? • A Punnett square highlights the four possible combinations of gametes and offspring that result from each cross. Blast Animation: Genetic Variation: Fusion of Gametes © 2010 Pearson Education, Inc.

P Generation Genetic makeup (alleles) Purple flowers Alleles carried PP White flowers pp by parents Gametes All P All p Figure 9. 6 -1

P Generation Genetic makeup (alleles) Purple flowers Alleles carried PP White flowers pp by parents Gametes All P All p F 1 Generation (hybrids) Purple flowers All Pp Alleles segregate Gametes 1 P 2 1 p 2 Figure 9. 6 -2

P Generation Genetic makeup (alleles) Purple flowers Alleles carried PP White flowers pp by parents Gametes All p All P F 1 Generation (hybrids) Purple flowers All Pp Alleles segregate Gametes 1 P 2 F 2 Generation (hybrids) Eggs from F 1 plant 1 p 2 Sperm from F 1 plant p P P p PP Pp Pp pp Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Figure 9. 6 -3

• Geneticists distinguish between an organism’s physical traits and its genetic makeup. – An organism’s physical traits are its phenotype. – An organism’s genetic makeup is its genotype. © 2010 Pearson Education, Inc.

Genetic Alleles and Homologous Chromosomes • Homologous chromosomes have – Genes at specific loci – Alleles of a gene at the same locus © 2010 Pearson Education, Inc.

Gene loci Homologous chromosomes Dominant allele P a B P a b Recessive allele Genotype: PP Homozygous for the dominant allele aa Homozygous for the recessive allele Bb Heterozygous Figure 9. 7

Mendel’s Law of Independent Assortment • A dihybrid cross is the crossing of parental varieties differing in two characters. • What would result from a dihybrid cross? Two hypotheses are possible: 1. Dependent assortment 2. Independent assortment Blast Animation: Two-Trait Crosses © 2010 Pearson Education, Inc.

(a) Hypothesis: Dependent assortment P Generation RRYY (b) Hypothesis: Independent assortment RRYY rryy Gametes RY ry F 1 Generation rryy Gametes RY Rr. Yy ry Rr. Yy Sperm F 2 Generation 1 1 r. Y RY 4 4 Sperm 1 2 RY 1 ry 2 1 2 RY Eggs 1 ry 2 Predicted results (not actually seen) 1 Ry 1 ry 4 4 1 RY 4 RRYY Rr. YY RRYy Rr. Yy 1 r. Y 4 Rr. YY rr. YY Rr. Yy rr. Yy 9 16 1 Ry 4 RRYy Rr. Yy RRyy Rryy 3 16 1 ry 4 3 16 1 16 Eggs Rr. Yy rr. Yy Rryy rryy Actual results (support hypothesis) Yellow round Green round Yellow wrinkled Green wrinkled Figure 9. 8

Figure 9. 8

• Mendel’s dihybrid cross supported the hypothesis that each pair of alleles segregates independently of the other pairs during gamete formation. • Thus, the inheritance of one character has no effect on the inheritance of another. • This is the law of independent assortment. • Independent assortment is also seen in two hereditary characters in Labrador retrievers. © 2010 Pearson Education, Inc.

Blind dog Phenotypes Black coat, blind (PRA) normal vision B_N_ Genotypes B_nn (a) Possible phenotypes of Labrador retrievers Blind dog Chocolate coat, normal vision bb. N_ Chocolate coat, blind (PRA) bbnn Mating of double heterozygotes (black coat, normal vision) Bb. Nn Phenotypic ratio of offspring 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA) (b) A Labrador dihybrid cross Figure 9. 9

Blind dog Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Blind dog Chocolate coat, normal vision bb. N_ Chocolate coat, blind (PRA) bbnn (a) Possible phenotypes of Labrador retrievers Figure 9. 9 a

Mating of double heterozygotes (black coat, normal vision) Bb. Nn Phenotypic ratio of offspring 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, 1 chocolate coat, blind (PRA) normal vision (b) A Labrador dihybrid cross Figure 9. 9 b

Using a Testcross to Determine an Unknown Genotype • A testcross is a mating between – An individual of dominant phenotype (but unknown genotype) – A homozygous recessive individual © 2010 Pearson Education, Inc.

Testcross Genotypes B_ bb Two possible genotypes for the black dog: BB Gametes B Offspring b Bb All black or Bb B b b Bb bb 1 black : 1 chocolate Figure 9. 10

The Rules of Probability • Mendel’s strong background in mathematics helped him understand patterns of inheritance. • The rule of multiplication states that the probability of a compound event is the product of the separate probabilities of the independent events. © 2010 Pearson Education, Inc.

F 1 Genotypes Bb female Bb male Formation of sperm Formation of eggs F 2 Genotypes Male gametes Female gametes 1 2 1 2 B B b B 1 1 4 1 ( 2 2 ) B b 1 4 b b 1 4 Figure 9. 11

Family Pedigrees • Mendel’s principles apply to the inheritance of many human traits. © 2010 Pearson Education, Inc.

DOMINANT TRAITS Widow’s peak Free earlobe No freckles Straight hairline Attached earlobe RECESSIVE TRAITS Freckles Figure 9. 12

Freckles No freckles Figure 9. 12 a

Widow’s peak Straight hairline Figure 9. 12 b

Free earlobe Attached earlobe Figure 9. 12 c

• Dominant traits are not necessarily – Normal or – More common • Wild-type traits are – Those seen most often in nature – Not necessarily specified by dominant alleles © 2010 Pearson Education, Inc.

• A family pedigree – Shows the history of a trait in a family – Allows geneticists to analyze human traits © 2010 Pearson Education, Inc.

First generation (grandparents) Second generation (parents, aunts, and uncles) Third generation (brother and sister) Female Male Attached Free Ff FF or Ff ff ff Ff Ff Ff ff ff FF or Ff Ff ff Figure 9. 13

Figure 9. 13 a

Figure 9. 13 b

Figure 9. 13 c

Human Disorders Controlled by a Single Gene • Many human traits – Show simple inheritance patterns – Are controlled by single genes on autosomes © 2010 Pearson Education, Inc.

Table 9. 1

Recessive Disorders • Most human genetic disorders are recessive. • Individuals who have the recessive allele but appear normal are carriers of the disorder. © 2010 Pearson Education, Inc.

Parents Hearing Dd Offspring D D Sperm d DD Hearing Dd Hearing (carrier) dd Deaf Eggs d Figure 9. 14

• Cystic fibrosis – Is the most common lethal genetic disease in the United States – Is caused by a recessive allele carried by about one in 25 people of European ancestry • Prolonged geographic isolation of certain populations can lead to inbreeding, the mating of close relatives. – Inbreeding increases the chance of offspring that are homozygous for a harmful recessive trait. © 2010 Pearson Education, Inc.

Dominant Disorders • Some human genetic disorders are dominant. – Huntington’s disease, which leads to degeneration of the nervous system, does not begin until middle age. – Achondroplasia is a form of dwarfism. – The homozygous dominant genotype causes death of the embryo. – Thus, only heterozygotes have this disorder. © 2010 Pearson Education, Inc.

Figure 9. 15

Parents Dwarf Normal (achondroplasia) (no achondroplasia) Dd dd d D Sperm d Dd Dwarf dd Normal Eggs d Molly Jo Matt Amy Zachary Jake Jeremy Figure 9. 16

Parents Normal (no achondroplasia) dd d D Dwarf (achondroplasia) Dd Sperm d Dd Dwarf dd Normal Eggs d Figure 9. 16 a

Molly Jo Matt Amy Zachary Jake Jeremy Figure 9. 16 b

The Process of Science: What Is the Genetic Basis of Hairless Dogs? • Observation: Dogs come in a wide variety of physical types. • Question: What is the genetic basis for the hairless phenotype? • Hypothesis: A comparison of genes of coated and hairless dogs would identify the gene or genes responsible. © 2010 Pearson Education, Inc.

• Prediction: A mutation in a single gene accounts for the hairless appearance. • Experiment: Compared DNA sequences of 140 hairless dogs from 3 breeds with 87 coated dogs from 22 breeds. • Results: Every hairless dog, but no coated dogs, had a single change in a single gene. © 2010 Pearson Education, Inc.

Figure 9. 17

Genetic Testing • Today many tests can detect the presence of disease-causing alleles. • Most genetic testing is performed during pregnancy. – Amniocentesis collects cells from amniotic fluid. – Chorionic villus sampling removes cells from placental tissue. • Genetic counseling helps patients understand the results and implications of genetic testing. © 2010 Pearson Education, Inc.

VARIATIONS ON MENDEL’S LAWS • Some patterns of genetic inheritance are not explained by Mendel’s laws. © 2010 Pearson Education, Inc.

Incomplete Dominance in Plants and People • In incomplete dominance, F 1 hybrids have an appearance in between the phenotypes of the two parents. © 2010 Pearson Education, Inc.

P Generation White rr Red RR Gametes R r Figure 9. 18 -1

P Generation White rr Red RR Gametes R r F 1 Generation Pink Rr Gametes 1 1 R 2 r 2 Figure 9. 18 -2

P Generation White rr Red RR Gametes R r F 1 Generation Pink Rr Gametes F 2 Generation 1 2 R Eggs 1 r 2 1 1 R 2 r 2 Sperm 1 1 R 2 r 2 RR Rr Rr rr Figure 9. 18 -3

• Hypercholesterolemia – Is characterized by dangerously high levels of cholesterol in the blood. – Is a human trait that is incompletely dominant. – Heterozygotes have blood cholesterol levels about twice normal. – Homozygotes have blood cholesterol levels about five times normal. © 2010 Pearson Education, Inc.

GENOTYPE PHENOTYPE HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors Mild disease Severe disease LDL receptor Cell Normal Figure 9. 19

ABO Blood Groups: An Example of Multiple Alleles and Codominance • The ABO blood groups in humans are an example of multiple alleles. © 2010 Pearson Education, Inc.

Blood Antibodies Reactions When Blood from Groups Below Is Group Genotypes Red Blood Cells Present in Mixed with Antibodies from Groups at Left (Phenotype) Blood A B AB O Carbohydrate A IAIA Anti-B A or IAi Carbohydrate B IBIB B Anti-A or IBi AB IAIB — O ii Anti-A Anti-B Figure 9. 20

Blood Group Genotypes (Phenotype) A IAIA or IAi B IBIB or IBi AB IAIB O ii Red Blood Cells Carbohydrate A Carbohydrate B Figure 9. 20 a

Antibodies Present in Blood Reactions When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O B AB A Anti-B Anti-A — Anti-A Anti-B Figure 9. 20 b

Figure 9. 20

• The immune system produces blood proteins called antibodies that can bind specifically to blood cell carbohydrates. • Blood cells may clump together if blood cells of a different type enter the body. • The clumping reaction is the basis of a blood-typing lab test. © 2010 Pearson Education, Inc.

Individual homozygous, for sickle-cell allele Sickle-cell (abnormal) hemoglobin Colorized SEM Abnormal hemoglobin crystallizes into long flexible chains, causing red blood cells to become sickle-shaped. Sickled cells can lead to a cascade of symptoms, such as weakness, pain, organ damage, and paralysis. Figure 9. 21

Figure 9. 21

• The human blood type alleles IA and IB exhibit codominance: Both alleles are expressed in the phenotype. © 2010 Pearson Education, Inc.

Pleiotropy and Sickle-Cell Disease • Pleiotropy is the impact of a single gene on more than one character. • Sickle-cell disease – Exhibits pleiotropy – Results in abnormal hemoglobin production – Causes disk-shaped red blood cells to deform into a sickle shape with jagged edges © 2010 Pearson Education, Inc.

P Generation aabbcc (very light) AABBCC (very dark) Aa. Bb. Cc F 1 Generation F 2 Generation 1 8 1 8 Sperm 1 1 8 8 1 8 1 8 Fraction of population 1 8 1 8 1 Eggs 8 1 8 1 8 1 64 6 64 15 64 20 64 15 64 6 64 1 64 Skin pigmentation Figure 9. 22

P Generation aabbcc (very light) AABBCC (very dark) Aa. Bb. Cc F 1 Generation F 2 Generation 1 8 1 64 6 64 1 8 Sperm 1 1 8 8 1 8 1 Eggs 8 1 8 1 8 15 64 20 64 15 64 6 64 1 64 Figure 9. 22 a

Fraction of population 20 64 15 64 6 64 1 64 Skin pigmentation Figure 9. 22 b

Polygenic Inheritance • Polygenic inheritance is the additive effects of two or more genes on a single phenotype. © 2010 Pearson Education, Inc.

Figure 9. 23

The Role of Environment • Many human characters result from a combination of heredity and environment. • Only genetic influences are inherited. © 2010 Pearson Education, Inc.

P Generation Round-yellow seeds (RRYY) r y Y Y Wrinkled-green seeds (rryy) R R y MEIOSIS r FERTILIZATION Gametes y R Y F 1 Generation R r y r All round-yellow seeds (Rr. Yy) Figure 9. 24 -1

P Generation Round-yellow seeds (RRYY) r y Y Y Wrinkled-green seeds (rryy) R R y MEIOSIS r FERTILIZATION Gametes y R Y F 1 Generation R r Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. R Y y r All round-yellow seeds (Rr. Yy) Law of Independent Assortment: Follow both the long and the short chromosomes. Y MEIOSIS r y Metaphase I (alternative arrangements) r Y R y They are arranged in either of two equally likely ways at metaphase I. Figure 9. 24 -2

P Generation Round-yellow seeds (RRYY) r y Y R R Y Wrinkled-green seeds (rryy) y MEIOSIS r FERTILIZATION Gametes y R Y F 1 Generation R r Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. R The R and r alleles segregate in anaphase I of meiosis. Only one long chromosome ends up in each gamete. Gametes Y y 1 RY 4 Law of Independent Assortment: Follow both the long and the short chromosomes. Metaphase I (alternative arrangements) r r R y MEIOSIS y Y R All round-yellow seeds (Rr. Yy) Y R Y r Metaphase II r 1 ry 4 Y R They are arranged in either of two equally likely ways at metaphase I. y r R Y y r r Y r r 1 r. Y 4 They sort independently, giving four gamete types. y y R R 1 Ry 4 Figure 9. 24 -3

P Generation Round-yellow seeds (RRYY) r y Y R R Y Wrinkled-green seeds (rryy) y MEIOSIS r FERTILIZATION Gametes y R Y F 1 Generation R r Law of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. R The R and r alleles segregate in anaphase I of meiosis. Only one long chromosome ends up in each gamete. Gametes y Law of Independent Assortment: Follow both the long and the short chromosomes. MEIOSIS Metaphase I (alternative arrangements) r y r Y y y Y R All round-yellow seeds (Rr. Yy) Y R Y Fertilization recombines the r and R alleles at random. F 2 Generation Y r R Y 1 ry 4 y Y r 1 r. Y 4 FERTILIZATION AMONG THE F 1 PLANTS 9 : 3 They are arranged in either of two equally likely ways at metaphase I. R r r R r Y y r 1 RY 4 Metaphase II r : 1 They sort independently, giving four gamete types. y y R R 1 Ry 4 Fertilization results in the 9: 3: 3: 1 phenotypic ratio in the F 2 generation. Figure 9. 24 -4

THE CHROMOSOMAL BASIS OF INHERITANCE • The chromosome theory of inheritance states that – Genes are located at specific positions on chromosomes – The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns • It is chromosomes that undergo segregation and independent assortment during meiosis and thus account for Mendel’s laws. © 2010 Pearson Education, Inc.

Dihybrid testcross Gray body, long wings (wild-type) Black body, short wings (mutant) Gg. Ll ggll Female Male Figure 9. 25 -1

Dihybrid testcross Gray body, long wings (wild-type) Black body, short wings (mutant) Gg. Ll ggll Female Male Results Offspring Gray-long Gg. Ll 965 Black-short ggll 944 Parental phenotypes 83% Gray-short Ggll 206 Black-long gg. Ll 185 Recombinant phenotypes 17% Figure 9. 25 -2

Linked Genes • Linked genes – Are located close together on a chromosome – May be inherited together • Using the fruit fly Drosophila melanogaster, Thomas Hunt Morgan determined that some genes were linked based on the inheritance patterns of their traits. © 2010 Pearson Education, Inc.

A B b a A B Parental gametes a b Pair of homologous chromosomes Crossing over A b a B Recombinant gametes Figure 9. 26

Genetic Recombination: Crossing Over • Crossing over can – Separate linked alleles – Produce gametes with recombinant chromosomes – Produce offspring with recombinant phenotypes © 2010 Pearson Education, Inc.

Gg. Ll (female) GL gl gl gl ggll (male) Crossing over GL Gl gl g. L gl Sperm Parental gametes Recombinant gametes Eggs FERTILIZATION Offspring GL gl Gl g. L gl gl Parental Recombinant Figure 9. 27

Gg. Ll (female) G L g l g l ggll (male) Crossing over G L gl Gl g L gl Sperm Parental gametes Recombinant gametes Eggs Figure 9. 27 a

GL Gl gl g. L gl Sperm Parental gametes Recombinant gametes Eggs FERTILIZATION Offspring G L gl Gl g L gl gl Parental Recombinant Figure 9. 27 b

• The percentage of recombinant offspring among the total is called the recombination frequency. © 2010 Pearson Education, Inc.

Chromosome g c l 17% 9% 9. 5% Recombination frequencies Figure 9. 28

Linkage Maps • Early studies of crossing over were performed using the fruit fly Drosophila melanogaster. • Alfred H. Sturtevant, a student of Morgan, developed a method for mapping gene loci, which resulted in the creation of linkage maps. – A diagram of relative gene locations on a chromosome is a linkage map. © 2010 Pearson Education, Inc.

Male Female 44 XY Somatic cells 22 Y 22 X Sperm 44 XX Offspring Female 44 XX 22 X Egg 44 XY Male Figure 9. 29

X Colorized SEM Y Figure 9. 29

SEX CHROMOSOMES AND SEX-LINKED GENES • Sex chromosomes influence the inheritance of certain traits. © 2010 Pearson Education, Inc.

Sex Determination in Humans • Nearly all mammals have a pair of sex chromosomes designated X and Y. – Males have an X and Y. – Females have XX. © 2010 Pearson Education, Inc.

Sex-Linked Genes • Any gene located on a sex chromosome is called a sex-linked gene. – Most sex-linked genes are found on the X chromosome. – Red-green color blindness is a common human sex-linked disorder. © 2010 Pearson Education, Inc.

Figure 9. 30

XNXN XNXn Xn Y XNY Sperm Xn XNXn Sperm XN Y Sperm Xn Y Eggs XN XNXn XNY Eggs XN XN XNXn XNY Xn XNXn Xn. Y Xn (a) Normal female colorblind male Key Unaffected individual Xn Y (b) Carrier female normal male Carrier Y XNXn XNY Xn Xn Xn Y (c) Carrier female colorblind male Colorblind individual Figure 9. 31

• Hemophilia – Is a sex-linked recessive blood-clotting trait that may result in excessive bleeding and death after relatively minor cuts and bruises – Has plagued royal families of Europe © 2010 Pearson Education, Inc.

Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9. 32

Evolution Connection: Barking Up the Evolutionary Tree • About 15, 000 years ago in East Asia, humans began to cohabit with ancestral canines that were predecessors of modern wolves and dogs. • As people settled into geographically distinct populations, different canines became separated and inbred. © 2010 Pearson Education, Inc.

• In 2005 researchers sequenced the complete genome of a dog. • An evolutionary tree of dog breeds was created. © 2010 Pearson Education, Inc.

Wolf Chinese shar-pei Ancestral canine Akita Basenji Siberian husky Alaskan malamute Afghan hound Saluki Rottweiler Sheepdog Retriever Figure 9. 33

Fertilization Alleles Meiosis Diploid cell (contains paired alleles, alternate forms of a gene) Gamete from other parent Diploid zygote (contains paired alleles) Haploid gametes (allele pairs separate) Figure 9. UN 1

Phenotype Genotype or Phenotype All dominant Conclusion Recessive pp Dominant P? Unknown parent is PP 1 dominant : 1 recessive Unknown parent is Pp Figure 9. UN 2

Dominant phenotype (RR) Recessive phenotype (rr) Intermediate phenotype (incomplete dominance) (Rr) Figure 9. UN 3

Single gene Pleiotropy Multiple traits (e. g. , sickle-cell disease) Figure 9. UN 4

Polygenic inheritance Single trait (e. g. , skin color) Multiple genes Figure 9. UN 5

Male 44 XY Female Somatic cells 44 XX Figure 9. UN 6

Figure 9. UN 7

Figure 9. UN 8