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Chapter 9 Patterns of Inheritance PowerPoint® 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. HERITABLE VARIATION AND PATTERNS OF INHERITANCE • Heredity is the transmission of traits from one generation to the next. • Gregor Mendel – Worked in the 1860s – Was the first person to analyze patterns of inheritance – Deduced the fundamental principles of genetics © 2010 Pearson Education, Inc. 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 • 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 F1 generation. – A cross of the F1 plants forms the F2 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. Planted seeds from pod. Offspring (F1) 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. • 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. 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 Seed color Seed shape Round Wrinkled Figure 9.4 P Generation (true-breading parents) Purple flowers White flowers Figure 9.5-1 P Generation (true-breading parents) Purple flowers F1 Generation White flowers All plants have purple flowers Figure 9.5-2 P Generation (true-breading parents) Purple flowers F1 Generation White flowers All plants have purple flowers Fertilization among F1 plants (F1 F1) F2 Generation 3 of plants 4 have purple flowers 1 of plants 4 have white flowers Figure 9.5-3 • Mendel developed four hypotheses from the monohybrid cross: 1. There are 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. 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 F1 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 F1 Generation (hybrids) Purple flowers All Pp Alleles segregate Gametes 1 P 2 F2 Generation (hybrids) Sperm from F1 plant p P P Eggs from F1 plant 1 p 2 PP Pp Pp pp p 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. 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 © 2010 Pearson Education, Inc. (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent assortment P Generation RRYY RRYY rryy Gametes RY ry F1 Generation rryy Gametes RY RrYy ry RrYy Sperm F2 Generation 1 1 rY 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 RrYY RRYy RrYy 1 rY 4 RrYY rrYY RrYy rrYy 9 16 1 Ry 4 RRYy RrYy RRyy Rryy 3 16 1 ry 4 3 16 1 16 Eggs RrYy rrYy Rryy rryy Actual results (support hypothesis) Yellow round Green round Yellow wrinkled Green wrinkled Figure 9.8 Blind dog Phenotypes Black coat, Black coat, blind (PRA) normal vision B_N_ Genotypes B_nn (a) Possible phenotypes of Labrador retrievers Blind dog Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn Mating of double heterozygotes (black coat, normal vision) BbNn BbNn 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 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. Phenotype Genotype Recessive pp Dominant P? or Phenotype All dominant Conclusion Unknown parent is PP 1 dominant : 1 recessive Unknown parent is Pp Figure 9.UN2 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 Family Pedigrees • Mendel’s principles apply to the inheritance of many human traits. © 2010 Pearson Education, Inc. • Dominant traits are not necessarily – Normal or – More common © 2010 Pearson Education, Inc. DOMINANT TRAITS Widow’s peak Free earlobe No freckles Straight hairline Attached earlobe RECESSIVE TRAITS Freckles Figure 9.12 • 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 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. Table 9.1 • 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. 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, F1 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 F1 Generation Pink Rr Gametes 1 1 R 2 r 2 Sperm 1 1 R 2 r 2 F2 Generation 1 2 R Eggs 1 r 2 RR Rr Rr rr Figure 9.18-3 Polygenic Inheritance • Polygenic inheritance is the additive effects of two or more genes on a single phenotype. Polygenic inheritance Single trait (e.g., skin color) Multiple genes © 2010 Pearson Education, Inc. P Generation aabbcc (very light) AABBCC (very dark) AaBbCc AaBbCc F1 Generation F2 Generation 1 8 1 8 1 8 Sperm 1 1 8 8 1 8 1 8 1 8 Fraction of population 1 8 1 8 1 8 1 Eggs 8 1 8 1 8 1 8 1 8 20 64 15 64 6 64 1 64 Skin pigmentation 1 64 6 64 15 64 20 64 15 64 6 64 1 64 Figure 9.22 The Role of Environment • Many human characters result from a combination of heredity and environment. • Only genetic influences are inherited. © 2010 Pearson Education, Inc. 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. A B a b A B Parental gametes a b A Pair of homologous chromosomes Crossing over b a B Recombinant gametes Figure 9.26 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. 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-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 XnY XNXn XNY Sperm Eggs XN XN X nY Sperm Sperm Y Y Xn Y XNXn XNY Eggs XN N XNXN X Y Eggs XN N XNXn X Y N XNXn X Y Xn n XNXn X Y Xn n XnXn X Y XN (a) Normal female colorblind male Key XNXn Unaffected individual Xn (b) Carrier female normal male Carrier (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 © 2010 Pearson Education, Inc. A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The F1 plants have yellow seeds. What is the expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross? A) 1:2:1 B) 2:1 C) 3:1 D) 9:3:3:1 E) 1:1 © 2010 Pearson Education, Inc. A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The F1 plants have yellow seeds. What is the expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross? A) 1:2:1 B) 2:1 C) 3:1 D) 9:3:3:1 E) 1:1 © 2010 Pearson Education, Inc. Alleles are described as ______. A) homologous chromosomes B) environmental factors that affect gene expression C) alternate versions of a gene D) Punnett squares E) alternate phenotypes © 2010 Pearson Education, Inc. Alleles are described as ______. A) homologous chromosomes B) environmental factors that affect gene expression C) alternate versions of a gene D) Punnett squares E) alternate phenotypes © 2010 Pearson Education, Inc. A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The seeds of all of the offspring are yellow. Why? A) The yellow allele is recessive to the green allele. B) All of the offspring are homozygous yellow. C) The yellow allele is dominant to the green allele. D) The alleles are codominant. E) Yellow is an easier color to produce. © 2010 Pearson Education, Inc. A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The seeds of all of the offspring are yellow. Why? A) The yellow allele is recessive to the green allele. B) All of the offspring are homozygous yellow. C) The yellow allele is dominant to the green allele. D) The alleles are codominant. E) Yellow is an easier color to produce. © 2010 Pearson Education, Inc. In humans, the presence or absence of dimples is a trait controlled by a single gene. What is the genotype of an individual who is heterozygous for dimples? A) dimples B) DD C) Dd D) dd E) DI © 2010 Pearson Education, Inc. In humans, the presence or absence of dimples is a trait controlled by a single gene. What is the genotype of an individual who is heterozygous for dimples? A) dimples B) DD C) Dd D) dd E) DI © 2010 Pearson Education, Inc. Which of these crosses will only produce heterozygous offspring? A) AA × aa B) AA × Aa C) Aa × Aa D) aa × aa E) Aa × aa © 2010 Pearson Education, Inc. Which of these crosses will only produce heterozygous offspring? A) AA × aa B) AA × Aa C) Aa × Aa D) aa × aa E) Aa × aa © 2010 Pearson Education, Inc. To determine the phenotype of an individual who expresses a dominant trait, you would cross that individual with an individual who ______. A) expresses the dominant trait B) is homozygous recessive for that trait C) has the genotype Aa D) is homozygous dominant for that trait E) is heterozygous for that trait © 2010 Pearson Education, Inc. To determine the phenotype of an individual who expresses a dominant trait, you would cross that individual with an individual who ______. A) expresses the dominant trait B) is homozygous recessive for that trait C) has the genotype Aa D) is homozygous dominant for that trait E) is heterozygous for that trait © 2010 Pearson Education, Inc. A couple has two female children. What is the probability that their next child will be male? A) 25% B) 50% C) 75% D) 33% E) 67% © 2010 Pearson Education, Inc. A couple has two female children. What is the probability that their next child will be male? A) 25% B) 50% C) 75% D) 33% E) 67% © 2010 Pearson Education, Inc. An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. What is the relationship between the alleles for hair texture? A) pleiotropy B) incomplete dominance C) straight hair and curly hair are sex-linked, but wavy hair is not D) wavy hair is dominant to both straight and curly hair E) codominance © 2010 Pearson Education, Inc. An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. What is the relationship between the alleles for hair texture? A) pleiotropy B) incomplete dominance C) straight hair and curly hair are sex-linked, but wavy hair is not D) wavy hair is dominant to both straight and curly hair E) codominance © 2010 Pearson Education, Inc. An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. If an individual with wavy hair mates with an individual with straight hair, what is the probability that their child will have curly hair? A) 0% B) 25% C) 50% D) 75% E) 100% © 2010 Pearson Education, Inc. An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their offspring have (naturally) wavy hair. If an individual with wavy hair mates with an individual with straight hair, what is the probability that their child will have curly hair? A) 0% B) 25% C) 50% D) 75% E) 100% © 2010 Pearson Education, Inc. Chromosomes that are not sex chromosomes are called ______. A) centrosomes B) allosomes C) nonsexosomes D) autosomes E) dominant © 2010 Pearson Education, Inc. Chromosomes that are not sex chromosomes are called ______. A) centrosomes B) allosomes C) nonsexosomes D) autosomes E) dominant © 2010 Pearson Education, Inc. The parents of a child with unusual disease symptoms take the child to a doctor for help. The doctor suspects that the condition might have a genetic basis. She recommends that the child be taken to a specialty clinic where physicians and staff members are trained to diagnose genetic diseases and counsel parents. Ultimately, the child is diagnosed with a rare recessively inherited disease. The parents are tested for the gene, and both are found to be heterozygous. The parents want to have another child but are afraid this child will also be affected. 4) What would genetic counselors say is the probability that the second child will have the disease? A) 1/2 B) 1/4 C) 1/8 D) 1/16 E) 1/32 © 2010 Pearson Education, Inc. The parents of a child with unusual disease symptoms take the child to a doctor for help. The doctor suspects that the condition might have a genetic basis. She recommends that the child be taken to a specialty clinic where physicians and staff members are trained to diagnose genetic diseases and counsel parents. Ultimately, the child is diagnosed with a rare recessively inherited disease. The parents are tested for the gene, and both are found to be heterozygous. The parents want to have another child but are afraid this child will also be affected. 4) What would genetic counselors say is the probability that the second child will have the disease? A) 1/2 B) 1/4 C) 1/8 D) 1/16 E) 1/32 © 2010 Pearson Education, Inc.