CAMPBELL BIOLOGY CONCEPTS CONNECTIONS NINTH EDITION Power Point
CAMPBELL BIOLOGY: CONCEPTS & CONNECTIONS, NINTH EDITION Power. Point Lectures Chapter 9 Patterns of Inheritance TAYLOR SIMON DICKEY HOGAN REECE © 2018 Pearson Education, Inc. Lecture by Edward J. Zalisko
Introduction • The Inuit people are indigenous to the arctic regions of Greenland, Canada, and Alaska. • The traditional Inuit diet, which is high in protein and very high in fat, consists of food obtained by hunting large land mammals. • What allows the Inuit people to tolerate high levels of dietary fat? The answer lies, at least in part, in their genes. © 2018 Pearson Education, Inc.
Figure 9. 0_1 © 2018 Pearson Education, Inc.
Figure 9. 0_2 Chapter 9: Big Ideas Mendel’s Laws Variations on Mendel’s Laws The Chromosomal Basis of Inheritance Sex Chromosomes and Sex-Linked Genes © 2018 Pearson Education, Inc.
MENDEL’S LAWS © 2018 Pearson Education, Inc.
9. 1 The study of genetics has ancient roots • Hippocrates’s idea that “pangenes” travel from each part of an organism’s body to the eggs or sperm is incorrect because • the reproductive cells are not composed of particles from somatic (body) cells and • changes in somatic cells do not influence gametes. • The blending hypothesis was rejected because it did not explain how traits that disappear in one generation can reappear in later generations. © 2018 Pearson Education, Inc.
9. 1 The study of genetics has ancient roots Checkpoint question Imagine you have two different birds of the same species, a female with a yellow beak and a male with a blue beak. Design a simple experiment to test the blending hypothesis. © 2018 Pearson Education, Inc.
Figure 9. 1 © 2018 Pearson Education, Inc.
9. 2 The science of genetics began in an abbey garden • Heredity is the transmission of traits from one generation to the next. • Genetics (the scientific study of heredity) began with Gregor Mendel’s experiments. • Mendel crossed pea plants and traced traits from generation to generation. • He hypothesized that there alternative versions of genes (alleles), the units that determine heritable traits. © 2018 Pearson Education, Inc.
9. 2 The science of genetics began in an abbey garden Checkpoint question Describe three generations of your own family using the terminology of a genetic cross (P, F 1, F 2). © 2018 Pearson Education, Inc.
Figure 9. 2 a © 2018 Pearson Education, Inc.
Figure 9. 2 b Petal Carpel (contains eggs) Stamens (release sperm-containing pollen) © 2018 Pearson Education, Inc.
Figure 9. 2 c_1 1 Stamen removed Parents (P) © 2018 Pearson Education, Inc. Carpel 2 Pollen transfer Stamens
Figure 9. 2 c_2 1 Stamen removed Parents (P) Carpel 2 Pollen transfer Stamens 3 Carpel matures into pod © 2018 Pearson Education, Inc.
Figure 9. 2 c_3 1 Stamen removed Parents (P) Carpel 2 Pollen transfer Stamens 3 Carpel matures into pod 4 Seed from pod planted 5 Offspring traits observed Offspring (F 1) © 2018 Pearson Education, Inc.
Figure 9. 2 d Character Flower color Traits Dominant Recessive Purple White Axial Terminal Yellow Green Round Wrinkled Inflated Constricted Green Yellow Tall Dwarf Flower position Seed color Seed shape Pod color Stem length © 2018 Pearson Education, Inc.
Figure 9. 2 d_1 Traits Character Dominant Recessive Purple White Axial Terminal Yellow Green Round Wrinkled Flower color Flower position Seed color Seed shape © 2018 Pearson Education, Inc.
Figure 9. 2 d_2 Character Traits Dominant Recessive Inflated Constricted Green Yellow Tall Dwarf Pod shape Pod color Stem length © 2018 Pearson Education, Inc.
9. 3 Mendel’s law of segregation describes the inheritance of a single character • Mendel developed four hypotheses, described below using modern terminology. 1. There alternative versions of genes (called alleles) that account for variations in inherited characters. 2. For each character, an organism inherits two alleles of a gene, one from each parent. • An organism that has two identical alleles for a gene is said to be homozygous for that gene. • An organism that has two different alleles for a gene is said to be heterozygous for that gene. © 2018 Pearson Education, Inc.
9. 3 Mendel’s law of segregation describes the inheritance of a single character 3. If the two alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele and the other has no noticeable effect on the organism’s appearance and is called the recessive allele. 4. A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation. © 2018 Pearson Education, Inc.
Figure 9. 3 a_1 The Experiment P generation (true-breeding parents) Purple flowers © 2018 Pearson Education, Inc. × White flowers
Figure 9. 3 a_2 The Experiment P generation (true-breeding parents) Purple flowers F 1 generation (hybrids) © 2018 Pearson Education, Inc. × White flowers All plants have purple flowers
Figure 9. 3 a_3 The Experiment P generation (true-breeding parents) Purple flowers F 1 generation (hybrids) × White flowers All plants have purple flowers Fertilization among F 1 plants (F 1 × F 1) F 2 generation 3 4 of plants have purple flowers © 2018 Pearson Education, Inc. 1 4 of plants have white flowers
9. 3 Mendel’s law of segregation describes the inheritance of a single character • Mendel’s hypotheses also explain the 3: 1 ratio observed in the F 2 generation. • The F 1 hybrids all have a Pp genotype. • A Punnett square shows the four possible combinations of alleles that could occur when these gametes combine. Checkpoint question How can two plants with different genotypes for a particular inherited character be identical in phenotype? © 2018 Pearson Education, Inc.
Figure 9. 3 b_1 The Explanation P generation Genetic makeup (alleles) Purple flowers White flowers PP pp Gametes © 2018 Pearson Education, Inc. All P All p
Figure 9. 3 b_2 The Explanation P generation Genetic makeup (alleles) Purple flowers White flowers PP pp Gametes All Pp F 1 generation Gametes © 2018 Pearson Education, Inc. All p 1 2 P Alleles segregate 1 2 p
Figure 9. 3 b_3 The Explanation P generation Genetic makeup (alleles) Purple flowers White flowers PP pp Gametes All p All Pp F 1 generation Gametes F 2 generation Results: Phenotypic ratio 3 purple: 1 white Genotypic ratio 1 PP: 2 Pp: 1 pp © 2018 Pearson Education, Inc. 1 2 P P p P PP Pp pp Sperm from F 1 plant Eggs from F 1 plant Alleles segregate Results 1 2 p
Figure 9. 3 b_4 F 2 generation Sperm from F 1 plant Results: Phenotypic ratio 3 purple: 1 white Genotypic ratio 1 PP: 2 Pp: 1 pp © 2018 Pearson Education, Inc. P Eggs from F 1 plant p PP Pp Pp pp Results
9. 4 Homologous chromosomes bear the alleles for each character • Every diploid cell has pairs of homologous chromosomes. • The chromosomes in a homologous pair carry alleles of the same genes at the same locations. Checkpoint question An individual is heterozygous, Bb, for a gene. According to the law of segregation, each gamete formed by this individual will have either the B allele or the b allele. Which step in the process of meiosis is the physical basis for this segregation of alleles? © 2018 Pearson Education, Inc.
Figure 9. 4 Gene loci Dominant allele P a B P a b Homologous chromosomes Genotype: PP Homozygous for the dominant allele © 2018 Pearson Education, Inc. aa Homozygous for the recessive allele Recessive allele Bb Heterozygous, with one dominant and one recessive allele
9. 5 The law of independent assortment is revealed by tracking two characters at once • A cross between two individuals that are heterozygous for one character is called a monohybrid cross. • A dihybrid cross is a mating of parental varieties that differ in two characters. • Mendel’s law of independent assortment states that the alleles of a pair segregate independently of other allele pairs during gamete formation. © 2018 Pearson Education, Inc.
Figure 9. 5 a P generation RRYY Gametes RY F 1 generation rryy × ry Rr. Yy Sperm 1 ry 4 1 RY 4 1 r. Y 4 1 Ry 4 RRYY Rr. YY RRYy Rr. YY rr. YY Rr. Yy rr. Yy Sperm 1 2 RY 1 ry 2 1 RY 2 F 2 generation Eggs 1 2 ry 1 RY 4 1 r. Y 4 Eggs 1 Ry 4 1 ry 4 The hypothesis of dependent assortment Not actually seen; hypothesis refuted © 2018 Pearson Education, Inc. Results: 9 16 3 16 RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy 3 16 1 16 The hypothesis of independent assortment Actual results; hypothesis supported Yellow round Green round Yellow wrinkled Green wrinkled
Figure 9. 5 a_1 P generation Gametes RY × F 1 generation © 2018 Pearson Education, Inc. rryy RRYY ry Rr. Yy
Figure 9. 5 a_2 F 1 generation 1 2 F 2 generation Rr. Yy Sperm 1 RY 2 ry RY Eggs 1 2 ry The hypothesis of dependent assortment Not actually seen; hypothesis refuted © 2018 Pearson Education, Inc.
Figure 9. 5 a_3 F 1 generation 1 RY 4 1 r. Y 4 Eggs 1 Ry 4 1 ry 4 Rr. Yy Sperm 1 RY 1 r. Y 1 Ry 4 4 4 1 ry 4 RRYY Rr. YY RRYy Rr. YY rr. YY Rr. Yy rr. Yy RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Results: 9 16 3 16 1 16 The hypothesis of independent assortment Actual results; hypothesis supported © 2018 Pearson Education, Inc. Yellow round Green round Yellow wrinkled Green wrinkled
Figure 9. 5 b Blind Phenotypes Black coat, normal vision Black coat, blind (PRA) Chocolate coat, normal vision Chocolate coat, blind (PRA) Genotypes B_N_ B_nn bb. N_ bbnn Mating of double heterozygotes (black coat, normal vision): Bb. Nn × Bb. Nn Blind 9 Phenotypic ratio Black coat, of the offspring normal vision © 2018 Pearson Education, Inc. 3 Black coat, blind (PRA) 3 Chocolate coat, normal vision 1 Chocolate coat, blind (PRA)
Figure 9. 5 b_1 Blind Phenotypes Black coat, normal vision Black coat, blind (PRA) Genotypes B_N_ B_nn Blind Phenotypes Chocolate coat, normal vision Chocolate coat, blind (PRA) Genotypes bb. N_ bbnn © 2018 Pearson Education, Inc.
Figure 9. 5 b_2 Mating of double heterozygotes (black coat, normal vision): Bb. Nn × Bb. Nn Blind Phenotypic ratio of the offspring 9 Black coat, normal vision 3 Black coat, blind (PRA) Blind Phenotypic ratio of the offspring © 2018 Pearson Education, Inc. 3 Chocolate coat, normal vision 1 Chocolate coat, blind (PRA)
9. 5 The law of independent assortment is revealed by tracking two characters at once Checkpoint question Predict the phenotypes of offspring obtained by mating a black Lab homozygous for both coat color and normal eyes with a chocolate Lab that is blind from PRA. © 2018 Pearson Education, Inc.
9. 6 Geneticists can use a testcross to determine unknown genotypes • The offspring of a testcross, a mating between an individual of unknown genotype and a homozygous recessive individual, can reveal the unknown genotype. Checkpoint question You use a testcross to determine the genotype of a Lab with normal eyes. Half of the offspring are normal and half develop PRA. What is the genotype of the normal parent? © 2018 Pearson Education, Inc.
Figure 9. 6 What is the genotype of the black dog? Testcross × Genotypes bb B_? Two possibilities for the black dog: BB Gametes B b Offspring © 2018 Pearson Education, Inc. Bb or Bb All black b Bb bb 1 black: 1 chocolate
9. 7 Mendel’s laws reflect the rules of probability • The rule of multiplication calculates the probability of two independent events both occurring. • The rule of addition calculates the probability of an event that can occur in alternative ways. Checkpoint question A plant of genotype AABb. CC is crossed with an Aa. Bb. Cc plant. What is the probability of an offspring having the genotype AABBCC? (Hint: Treat this as 3 separate monohybrid crosses. ) © 2018 Pearson Education, Inc.
Figure 9. 7 F 1 genotypes Bb male Bb female Formation of eggs Formation of sperm 1 2 B b Sperm 1 1 (2 × 2) 1 2 F 2 genotypes B b b b 1 4 B 1 4 © 2018 Pearson Education, Inc. B 1 4 Eggs 1 2 B B b b 1 4
9. 8 VISUALIZING THE CONCEPT: Genetic traits in humans can be tracked through family pedigrees • The inheritance of many human traits follows Mendel’s laws. • Family pedigrees can help determine individual genotypes. Checkpoint question If Libby had a child, which phenotype would allow her to deduce her own genotype for certain? © 2018 Pearson Education, Inc.
Figure 9. 8_1 Straight hairline © 2018 Pearson Education, Inc. Widow’s peak
Figure 9. 8_2 Female Mating Widow’s peak hairline trait Straight hairline trait H: widow’s peak allele h: straight allele 1 ST GENERATION Al Beth Charles Children Evelyn Frank Gary Isabel Julia Widow’s peak 3 RD GENERATION Kristin © 2018 Pearson Education, Inc. 2 ND GENERATION Henry Straight hairline Debbie Libby
Figure 9. 8_3 Female Male Widow’s peak hairline trait Straight hairline trait H: widow’s peak allele h: straight allele 1 ST GENERATION Al Beth Charles Debbie Hh Hh hh Hh 2 ND GENERATION Evelyn Hh or Hh Frank Gary Henry hh hh Hh Straight hairline Isabel Julia Hh hh 3 RD GENERATION Kristin hh © 2018 Pearson Education, Inc. A parent with a widow’s peak who has a child with a straight hairline must be Hh. Kristin has a straight Libby hairline but her parents do not, so straight hairline HH must be homozygous or recessive (hh). Hh Widow’s peak
Figure 9. 8_4 Female Male Widow’s peak hairline trait Straight hairline trait H: widow’s peak allele h: straight allele 1 ST GENERATION Al Beth Charles Debbie Hh Hh hh Hh 2 ND GENERATION Evelyn Hh or Hh Frank Gary Henry Isabel Julia hh hh Hh Hh hh Straight hairline © 2018 Pearson Education, Inc. 3 RD GENERATION Not all genotypes can be determined. Libby could be Libby Kristin HH or Hh and there is no HH hh way to know (unless she or has some children and the pedigree is extended). Hh Widow’s peak
9. 9 CONNECTION: Many inherited traits in humans are controlled by a single gene • The genetic disorders listed in Table 9. 9 are known to be inherited as dominant or recessive traits controlled by a single gene. • Most people who have recessive disorders are born to normal parents who are both heterozygotes —that is, parents who are carriers of the recessive allele for the disorder but are phenotypically normal. © 2018 Pearson Education, Inc.
Table 9. 9 © 2018 Pearson Education, Inc.
9. 9 CONNECTION: Many inherited traits in humans are controlled by a single gene Checkpoint question Peter is a 30 -year-old man whose father died of Huntington’s disease. Neither Peter’s mother nor a much older sister shows any signs of Huntington’s. What is the probability that Peter has inherited Huntington’s disease? © 2018 Pearson Education, Inc.
Figure 9. 9 a Dominant Traits Recessive Traits © 2018 Pearson Education, Inc. Freckles No freckles Normal pigmentation Albinism More common Less common
Figure 9. 9 a_1 Freckles © 2018 Pearson Education, Inc.
Figure 9. 9 a_2 No freckles © 2018 Pearson Education, Inc.
Figure 9. 9 a_3 Normal pigmentation © 2018 Pearson Education, Inc.
Figure 9. 9 a_4 Albinism © 2018 Pearson Education, Inc.
Figure 9. 9 b Normal Aa Parents A A Offspring × Sperm a AA Normal Aa Normal (carrier) aa Albinism Eggs a © 2018 Pearson Education, Inc. Normal Aa
Figure 9. 9 c © 2018 Pearson Education, Inc.
9. 10 CONNECTION: New technologies can provide insight into one’s genetic legacy • Carrier screening, fetal testing, fetal imaging, and newborn screening can provide information for reproductive decisions but may create ethical dilemmas. Checkpoint question What is the primary benefit of genetic screening by CVS? What is the primary risk? © 2018 Pearson Education, Inc.
Figure 9. 10 a Amniocentesis Chorionic Villus Sampling (CVS) Ultrasound Suction tube Needle extracts transducer extracts tissue amniotic fluid. Ultrasound from chorionic villi. transducer Fetus Placenta Uterus Chorionic villi Cervix Centrifugation Cervix Uterus Amniotic fluid Fetal cells Cultured cells Fetal cells Several hours Several weeks Biochemical and genetic tests Several weeks Several hours Karyotyping © 2018 Pearson Education, Inc. Several hours
Figure 9. 10 a_1 Karyotyping © 2018 Pearson Education, Inc.
Figure 9. 10 b © 2018 Pearson Education, Inc.
Figure 9. 10 b_1 © 2018 Pearson Education, Inc.
Figure 9. 10 b_2 © 2018 Pearson Education, Inc.
Video: Ultrasound of Human Fetus © 2018 Pearson Education, Inc.
VARIATIONS ON MENDEL’S LAWS © 2018 Pearson Education, Inc.
9. 11 Incomplete dominance results in intermediate phenotypes • Mendel’s laws are valid for all sexually reproducing species, but genotype often does not dictate phenotype in the simple way Mendel’s laws describe. • Mendel’s pea crosses always looked like one of the two parental varieties, a situation called complete dominance. • For some characters, the appearance of F 1 hybrids falls between the phenotypes of the two parental varieties. This is called incomplete dominance. © 2018 Pearson Education, Inc.
Figure 9. 11 a P generation × Red RR Gametes R r F 1 generation Pink hybrid Rr Gametes 1 2 R F 2 generation Sperm 1 2 R 1 2 r 1 2 R RR r. R 1 2 r Rr rr Eggs © 2018 Pearson Education, Inc. White rr r
Figure 9. 11 a_1 P generation × Red RR Gametes R © 2018 Pearson Education, Inc. r White rr
Figure 9. 11 a_2 P generation × Red RR Gametes R F 1 generation Gametes © 2018 Pearson Education, Inc. r White rr Pink hybrid Rr 1 2 R 1 2 r
Figure 9. 11 a_3 P generation × Red RR Gametes R r F 1 generation Pink hybrid Rr Gametes 1 2 R F 2 generation Sperm 1 2 R 1 2 r 1 2 R RR r. R 1 2 r Rr rr Eggs © 2018 Pearson Education, Inc. White rr r
Checkpoint question Why doesn’t the cross shown in Figure 9. 11 A support the blending hypothesis? © 2018 Pearson Education, Inc.
Figure 9. 11 b Genotypes HH hh Hh Homozygous Heterozygous Homozygous for ability to make for inability to LDL receptors make LDL receptors Phenotypes LDL receptor Cell Normal © 2018 Pearson Education, Inc. Mild disease Severe disease
9. 12 Many genes have more than two alleles that may be codominant • The ABO blood group phenotype in humans is controlled by three alleles that produce a total of four phenotypes. • The IA and IB alleles are codominant: Both alleles are expressed in heterozygous individuals (IAIB), who have type AB blood. © 2018 Pearson Education, Inc.
9. 12 Many genes have more than two alleles that may be codominant Checkpoint question Maria has type O blood, and her sister has type AB blood. The girls know that both of their maternal grandparents are type A. What are the genotypes of the girls’ parents? © 2018 Pearson Education, Inc.
Figure 9. 12 Blood Group (Phenotype) Genotypes Carbohydrates Present on Red Blood Cells A IA IA or I Ai Carbohydrate A Carbohydrate B B IB I B or I Bi Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB Anti-A Carbohydrate A AB IA I B O ii and Carbohydrate B Neither None Anti-A Anti-B No reaction © 2018 Pearson Education, Inc. Clumping reaction
Figure 9. 12_1 Blood Group (Phenotype) Genotypes Carbohydrates Present on Red Blood Cells A IA IA or IAi Carbohydrate A Carbohydrate B B IB I B or IBi Carbohydrate A AB IA I B and Carbohydrate B O © 2018 Pearson Education, Inc. ii Neither
Figure 9. 12_2 Blood Group (Phenotype) Antibodies Present in Blood A Anti-B B Anti-A AB None Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB Anti-A O Anti-B No reaction © 2018 Pearson Education, Inc. Clumping reaction
9. 13 A single gene may affect many phenotypic characters • Pleiotropy occurs when one gene influences multiple characters. • Sickle-cell disease is a human example of pleiotropy. • This disease affects the type of hemoglobin produced and the shape of red blood cells, and causes anemia and organ damage. • Sickle-cell and nonsickle alleles are codominant. • Carriers of sickle-cell disease have increased resistance to malaria. © 2018 Pearson Education, Inc.
9. 13 A single gene may affect many phenotypic characters Checkpoint question Why is the sickle-cell trait considered codominant at the molecular level? © 2018 Pearson Education, Inc.
SEM 1, 045× Figure 9. 13 a © 2018 Pearson Education, Inc.
Figure 9. 13 b An individual homozygous for the sickle-cell allele Produces sickle-cell (abnormal) hemoglobin The abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped The mutiple effects of sickled cells Damage to organs Kidney failure Heart failure Spleen damage Brain damage (impaired mental function, paralysis) © 2018 Pearson Education, Inc. Other effects Pain and fever Joint problems Physical weakness Anemia Pneumonia and other infections
9. 14 A single character may be influenced by many genes • Many characters result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes on a single phenotypic character. • Human skin color is an example of polygenic inheritance. © 2018 Pearson Education, Inc.
9. 14 A single character may be influenced by many genes Checkpoint question An Aa. Bbcc individual would be indistinguishable in phenotype from which of the following individuals: AAbbcc, aa. BBcc, Aabb. Cc, Aabbcc, or aa. Bb. Cc? © 2018 Pearson Education, Inc.
Figure 9. 14 × P generation AABBCC (very dark) aabbcc (very light) F 1 generation × Aa. Bb. Cc (medium shade) Sperm Eggs 1 64 © 2018 Pearson Education, Inc. 1 8 1 8 1 8 1 8 Fraction of population F 2 generation 1 8 6 64 15 64 20 64 15 64 6 64 1 64 Skin color
Figure 9. 14_1 P generation × aabbcc AABBCC (very light) (very dark) F 1 generation × Aa. Bb. Cc (medium shade) © 2018 Pearson Education, Inc. Aa. Bb. Cc (medium shade)
Figure 9. 14_2 Sperm F 2 generation Eggs 1 8 1 8 1 8 1 8 1 64 © 2018 Pearson Education, Inc. 6 64 15 64 20 64 15 64 6 64 1 64
Figure 9. 14_3 Fraction of population 20 64 15 64 6 64 1 64 Skin color © 2018 Pearson Education, Inc.
9. 15 The environment affects many characters • Many traits are affected, in varying degrees, by both genetic and environmental factors. Checkpoint question If most characters result from a combination of environment and heredity, why was Mendel able to ignore environmental influences in his pea plants? © 2018 Pearson Education, Inc.
Figure 9. 15 a © 2018 Pearson Education, Inc.
Figure 9. 15 b © 2018 Pearson Education, Inc.
THE CHROMOSOMAL BASIS OF INHERITANCE © 2018 Pearson Education, Inc.
9. 16 Chromosome behavior accounts for Mendel’s laws • The chromosome theory of inheritance states that • genes occupy specific loci (positions) on chromosomes and • chromosomes undergo segregation and independent assortment during meiosis. • Mendel’s laws correlate with chromosome separation in meiosis. © 2018 Pearson Education, Inc.
9. 16 Chromosome behavior accounts for Mendel’s laws Checkpoint question Which of Mendel’s laws have their physical basis in the following phases of meiosis: (a) the orientation of homologous chromosome pairs in metaphase I; (b) the separation of homologous chromosomes in anaphase I? © 2018 Pearson Education, Inc.
Figure 9. 16_1_1 F 1 generation R r Y R Y © 2018 Pearson Education, Inc. r y y All yellow round seeds (Rr. Yy) r Two equally probable Y arrangements of chromosomes at metaphase I R y
Figure 9. 16_1_2 F 1 generation R r y Y R Y © 2018 Pearson Education, Inc. R r Y y r r y All yellow round seeds (Rr. Yy) Two equally probable Y arrangements of chromosomes at metaphase I Anaphase I R r Y y Metaphase II R y r Y R y r R Y y
Figure 9. 16_1_3 F 1 generation R r All yellow round seeds (Rr. Yy) y Y Meiosis II y Y R r Y y r r R Two equally probable Y arrangements of chromosomes at metaphase I R y Anaphase I R r Y y Metaphase II r Y R y r R Y y Gametes Y y Y R R 1 RY 4 r Y Y r r r 1 r. Y 4 1 ry 4 Fertilization among the F 1 plants F 2 generation 9 © 2018 Pearson Education, Inc. y : 3 : 1 y y R R 1 Ry 4
Figure 9. 16_2 Sperm 1 1 Ry r. Y RY 4 4 4 ry 4 Eggs 1 4 RY RRYY Rr. YY RRYy Rr. Yy 1 4 r. Y Rr. YY rr. YY Rr. Yy rr. Yy 1 4 Ry 1 ry 4 © 2018 Pearson Education, Inc. RRYy Rr. Yy RRyy Rr. Yy rr. Yy Rryy rryy Green round 9 Yellow 16 round 3 16 3 Yellow 16 wrinkled 1 Green 16 wrinkled
9. 17 SCIENTIFIC THINKING: Genes on the same chromosome tend to be inherited together • Bateson and Punnett studied plants that did not show a 9: 3: 3: 1 ratio in the F 2 generation. What they found was an example of linked genes, which • are located close together on the same chromosome and • tend to be inherited together. © 2018 Pearson Education, Inc.
9. 17 SCIENTIFIC THINKING: Genes on the same chromosome tend to be inherited together Checkpoint question In what way was Bateson and Punnett’s success dependent upon failing at first? © 2018 Pearson Education, Inc.
Figure 9. 17 The Experiment Purple flower Pp. Ll × Phenotypes Purple long Purple round Red long Red round Pp. Ll Observed offspring 284 21 21 55 Long pollen Prediction (9: 3: 3: 1) The Explanation: Linked Genes PL Parental diploid cell Pp. Ll pl Meiosis Most gametes pl PL 215 71 71 24 Fertilization Sperm PL pl PL PL PL pl pl pl PL Most offspring Eggs pl 3 purple long: 1 red round Not accounted for: purple round and red long © 2018 Pearson Education, Inc.
Figure 9. 17_1 The Experiment Purple flower Pp. Ll Phenotypes Purple long Purple round Red long Red round © 2018 Pearson Education, Inc. × Pp. Ll Observed offspring 284 21 21 55 Long pollen Prediction (9: 3: 3: 1) 215 71 71 24
Figure 9. 17_2 The Explanation: Linked Genes PL Parental diploid cell Pp. Ll pl Meiosis Most gametes pl PL Fertilization Sperm PL pl Most offspring PL PL PL pl pl pl PL Eggs pl 3 purple long: 1 red round Not accounted for: purple round and red long © 2018 Pearson Education, Inc.
9. 18 Crossing over produces new combinations of alleles • Crossing over between homologous chromosomes produces new combinations of alleles in gametes. • Linked genes can be separated by crossing over, forming recombinant gametes. • The percentage of recombinant offspring among the total is the recombination frequency. © 2018 Pearson Education, Inc.
Figure 9. 18 a P L p l P L Parental gametes p l Tetrad Crossing over (pair of homologous chromosomes) © 2018 Pearson Education, Inc. p L P l Recombinant gametes
Figure 9. 18 b © 2018 Pearson Education, Inc.
Figure 9. 18 c The Experiment The Explanation Black body, vestigial wings Gray body, long wings (wild type) Gg. Ll × Gg. Ll Female Male g l g l gl GL Gray long Black vestigial Gray vestigial Black long Parental phenotypes 206 185 Recombinant phenotypes 391 recombinants Recombination frequency = = 0. 17 or 17% 2, 300 total offspring © 2018 Pearson Education, Inc. gl × Sperm Offspring GL gl Gl g. L gl gl Parental 944 g. L Gl Eggs Offspring 965 ggll Male Crossing over ggll Female GL G = gray body (dominant) g = black body (recessive) Recombinant L = long wings (dominant) l = vestigial wings (recessive)
Figure 9. 18 c_1 The Experiment Black body, vestigial wings Gray body, long wings (wild type) × Gg. Ll ggll Male Female Offspring Gray long Black vestigial 965 944 Parental phenotypes Recombination frequency = © 2018 Pearson Education, Inc. Gray vestigial Black long 206 185 Recombinant phenotypes 391 recombinants = 0. 17 or 17% 2, 300 total offspring
Figure 9. 18 c_2 The Explanation Gg. Ll Female GL g l g l ggll Male Crossing over gl GL Gl g. L Eggs × Sperm GL Offspring g l Gl g. L g l g l Parental © 2018 Pearson Education, Inc. gl g l Recombinant
Checkpoint question Return to the data in Figure 9. 17. What is the recombination frequency between the flower-color and pollen-length genes? © 2018 Pearson Education, Inc.
9. 19 Geneticists use crossover data to map genes • Recombination frequencies can be used to map the relative positions of genes on chromosomes. • A genetic map is an ordered list of the genetic loci along a chromosome. • Such a genetic map based on recombinant frequencies is called a linkage map. © 2018 Pearson Education, Inc.
Figure 9. 19 a Section of chromosome carrying linked genes g c l 17% 9% 9. 5% Recombination frequencies © 2018 Pearson Education, Inc.
Figure 9. 19 b Mutant (less common) phenotypes Short Maroon aristae eyes Long aristae Red (appendages eyes on head) Black Cinnabar Vestigial Down- Brown body eyes wings curved eyes (c) (g) (l) wings Gray body (G) Red Normal eyes wings (C) (L) Normal Red wings eyes Wild-type (more common) phenotypes © 2018 Pearson Education, Inc.
Checkpoint question You design Drosophila crosses to provide recombination data for a gene not included in Figure 9. 19 A. The gene has recombination frequencies of 3% with the vestigialwing (l) locus and 7% with the cinnabar-eye (c) locus. Where is it located on the chromosome? © 2018 Pearson Education, Inc.
SEX CHROMOSOMES AND SEX-LINKED GENES © 2018 Pearson Education, Inc.
9. 20 Chromosomes determine sex in many species • In mammals, a male has XY sex chromosomes, and a female has XX. • The Y chromosome has genes for the development of testes, whereas an absence of the Y allows ovaries to develop. • In addition, human males and females both have 44 autosomes (nonsex chromosomes). • Other systems of sex determination exist in other animals and plants. © 2018 Pearson Education, Inc.
9. 20 Chromosomes determine sex in many species • In some animals, environmental temperature determines the sex. • For some reptiles, the temperature at which eggs are incubated during a specific period of embryonic development determines whether that embryo will develop into a male or female. • Global climate change may therefore impact the sex ratio of such species. © 2018 Pearson Education, Inc.
9. 20 Chromosomes determine sex in many species Checkpoint question King Henry VIII of England was quick to blame his wives for bearing him only daughters. Explain how, from a genetic point of view, his thinking was wrong. © 2018 Pearson Education, Inc.
Table 9. 20 © 2018 Pearson Education, Inc.
Table 9. 20_1 X-O system © 2018 Pearson Education, Inc.
Table 9. 20_2 Z-W system © 2018 Pearson Education, Inc.
Table 9. 20_3 Chromosome number determines sex © 2018 Pearson Education, Inc.
X Y © 2018 Pearson Education, Inc. Colorized SEM 31, 955× Figure 9. 20 a
Figure 9. 20 b Parents (diploid) Gametes (haploid) Male 44 + XY 22 + X Female 44 + XY 22 + Y Sperm Offspring (diploid) © 2018 Pearson Education, Inc. 44 + XX Female 22 + Y Egg 44 + XY Male
Figure 9. 20 b_1 © 2018 Pearson Education, Inc.
Figure 9. 20 b_2 © 2018 Pearson Education, Inc.
Figure 9. 20 b_3 © 2018 Pearson Education, Inc.
Figure 9. 20 b_4 © 2018 Pearson Education, Inc.
9. 21 Sex-linked genes exhibit a unique pattern of inheritance • A gene located on either sex chromosome is called a sex-linked gene. • The X chromosome carries many X-linked genes that control traits unrelated to sex. • The inheritance of white eye color in the fruit fly illustrates an X-linked recessive trait. © 2018 Pearson Education, Inc.
9. 21 Sex-linked genes exhibit a unique pattern of inheritance Checkpoint question A white-eyed female Drosophila is mated with a red-eyed (wild-type) male. What result do you predict for the numerous offspring? © 2018 Pearson Education, Inc.
© 2018 Pearson Education, Inc. 35× Figure 9. 21 a
Figure 9. 21 a_1 © 2018 Pearson Education, Inc.
Figure 9. 21 a_2 © 2018 Pearson Education, Inc.
Figure 9. 21 b Female Male X RX R X r. Y × Sperm Eggs XR © 2018 Pearson Education, Inc. Xr Y X RX r X RY R = red-eye allele r = white-eye allele
Figure 9. 21 c Female Male X RX r X RY × Sperm XR XR Y X RX R X RY X r. X R X r. Y Eggs Xr © 2018 Pearson Education, Inc. R = red-eye allele r = white-eye allele
Figure 9. 21 d Female Male X RX r X r. Y × Sperm XR Xr Y X RX r X RY X r. Y Eggs Xr © 2018 Pearson Education, Inc. R = red-eye allele r = white-eye allele
9. 22 CONNECTION: Human sex-linked disorders affect mostly males • Most X-linked human disorders are due to recessive alleles and therefore are seen mostly in males. • A male receiving a single X-linked recessive allele from his mother will have the disorder. • A female must receive the allele from both parents to be affected. © 2018 Pearson Education, Inc.
9. 22 CONNECTION: Human sex-linked disorders affect mostly males Checkpoint question Neither Tom nor Sue has hemophilia, but their first son does. If the couple has a second child, what is the probability that he or she will also have the disease? © 2018 Pearson Education, Inc.
Figure 9. 22 Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Female Male Hemophilia Alexis Carrier Normal © 2018 Pearson Education, Inc.
Figure 9. 22_1 © 2018 Pearson Education, Inc.
9. 23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolution • Y chromosomes can provide data about recent human evolutionary history because they are passed on intact from father to son. © 2018 Pearson Education, Inc.
9. 23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolution • In 2003, geneticists discovered that about 8% of males currently living in central Asia have Y chromosomes of striking genetic similarity. • Further analysis traced their common genetic heritage to a man living about 1, 000 years ago. • In combination with historical records, the data led to the speculation that the Mongolian ruler Genghis Khan may be responsible for the spread of the telltale chromosome to nearly 16 million male descendants. © 2018 Pearson Education, Inc.
Figure 9. 23 © 2018 Pearson Education, Inc.
You should now be able to 1. Describe theory of pangenes and the blending hypothesis. Explain why both ideas are now rejected. 2. Define and distinguish between true-breeding organisms, hybrids, the P generation, the F 1 generation, and the F 2 generation. © 2018 Pearson Education, Inc.
You should now be able to 3. Define and distinguish between the following pairs of terms: • • homozygous and heterozygous; dominant allele and recessive allele; genotype and phenotype. Also, define a monohybrid cross and a Punnett square. © 2018 Pearson Education, Inc.
You should now be able to 4. Explain how Mendel’s law of segregation describes the inheritance of a single character. 5. Describe the genetic relationships between homologous chromosomes. 6. Explain how Mendel’s law of independent assortment applies to a dihybrid cross. 7. Explain how and when the rule of multiplication and the rule of addition can be used to determine the probability of an event. © 2018 Pearson Education, Inc.
You should now be able to 8. Explain how family pedigrees can help determine the inheritance of many human traits. 9. Explain how recessive and dominant disorders are inherited. Provide examples of each. 10. Compare the health risks, advantages, and disadvantages of the following forms of fetal testing: • amniocentesis, • chorionic villus sampling, and • ultrasound imaging. © 2018 Pearson Education, Inc.
You should now be able to 11. Describe the inheritance patterns of incomplete dominance, multiple alleles, codominance, pleiotropy, and polygenic inheritance. 12. Explain how the sickle-cell allele can be adaptive. 13. Explain why human skin coloration is not sufficiently explained by polygenic inheritance. 14. Define the chromosome theory of inheritance. Explain the chromosomal basis of the laws of segregation and independent assortment. © 2018 Pearson Education, Inc.
You should now be able to 15. Explain how linked genes are inherited differently from nonlinked genes. 16. Describe T. H. Morgan’s studies of crossing over in fruit flies. Explain how Sturtevant created linkage maps. 17. Explain how sex is genetically determined in humans and the significance of the SRY gene. 18. Describe patterns of sex-linked inheritance and examples of sex-linked disorders. 19. Explain how the Y chromosome can be used to trace human ancestry. © 2018 Pearson Education, Inc.
Figure 9. UN 01 Homologous chromosomes Alleles, residing at the same locus Meiosis Paired alleles, different forms of a gene © 2018 Pearson Education, Inc. Fertilization + Gamete Diploid zygote from the (containing other parent paired alleles) Haploid gametes (allele pairs separated)
Figure 9. UN 02 Incomplete dominance × Red RR © 2018 Pearson Education, Inc. White rr Pink Rr
Figure 9. UN 03 Single gene © 2018 Pearson Education, Inc. Pleiotropy Multiple characters
Figure 9. UN 04 Multiple genes © 2018 Pearson Education, Inc. Polygenic inheritance Single characters (such as skin color)
Figure 9. UN 05 Genes alternative versions called located on chromosomes at specific locations called (b) (a) if both are the same, the genotype is called if different, the genotype is called (c) heterozygous the expressed allele is called (d) the unexpressed allele is called (e) inheritance when the phenotype is in-between is called (f) © 2018 Pearson Education, Inc.
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