Patterns of Inheritance

Transcription

1 Chapte 9 Pattens of Inheitance HERITABLE VARIATION AND PATTERNS OF INHERITANCE Heedity is the tansmission of taits fom one geneation to the next. Genetics is the scientific study of heedity. Gego Mendel woked in the 60s, PowePoint Lectues fo Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fouth Edition Eic J. Simon, Jean L. Dickey, and Jane B. Reece Lectues by Edwad J. Zalisko 03 Peason Education, Inc. was the fist peson to analyze pattens of inheitance, and deduced the fundamental pinciples of genetics. 03 Peason Education, Inc. Biology and Society: Ou Longest-Running Genetic Expeiment: Dogs Figue 9. People have selected and mated dogs with pefeed taits fo moe than 5,000 yeas. Ove thousands of yeas, such genetic tinkeing has led to the incedible vaiety of body types and behavios in dogs today. The biological pinciples undelying genetics have only ecently been undestood. 03 Peason Education, Inc. Figue 9.0 Figue 9.5a

2 In an Abbey Gaden Mendel studied gaden peas because they wee easy to gow, came in many eadily distinguishable vaieties, ae easily manipulated, and can self-fetilize. Figue 9.3- Paents (P) Capel Removed stamens fom puple flowe. Stamens Tansfeed pollen fom stamens of white flowe to capel of puple flowe. 3 Pollinated capel matued into pod. 03 Peason Education, Inc. Figue 9. Figue Removed stamens fom puple flowe. Petal Stamen (makes spempoducing pollen) Capel (poduces eggs) Paents (P) Capel Offsping (F) 3 Stamens Tansfeed pollen fom stamens of white flowe to capel of puple flowe. Pollinated capel matued into pod. Planted seeds fom pod. Figue 9.3- Paents (P) Capel Removed stamens fom puple flowe. Stamens Tansfeed pollen fom stamens of white flowe to capel of puple flowe. In an Abbey Gaden A chaacte is a heitable featue that vaies among individuals. A tait is a vaiant of a chaacte. Each of the chaactes Mendel studied occued in two distinct taits. 03 Peason Education, Inc.

3 In an Abbey Gaden Figue 9. Mendel ceated puebed vaieties of plants and cossed two diffeent puebed vaieties. Flowe colo Flowe position Dominant Puple Recessive White Pod shape Pod colo Dominant Inflated Geen Recessive Consticted Yellow Seed colo Seed shape Axial Yellow Round Teminal Geen Winkled Stem length Tall Dwaf 03 Peason Education, Inc. In an Abbey Gaden Figue 9.a Hybids ae the offsping of two diffeent puebed vaieties. The paental plants ae the P geneation. Thei hybid offsping ae the F geneation. A coss of the F plants foms the F geneation. 03 Peason Education, Inc. Mendel s Law of Segegation Monohybid Cosses Mendel pefomed many expeiments. He tacked the inheitance of chaactes that occu as two altenative taits. A monohybid coss is a coss between puebed paent plants that diffe in only one chaacte Peason Education, Inc. 03 Peason Education, Inc.

4 Figue P Geneation (puebed paents) Puple flowes White flowes F Geneation All plants have puple flowes Fetilization among F plants (F F) F Geneation 03 Peason Education, Inc. Blast Animation: Single-Tait Cosses Select Play 3 of plants have puple flowes of plants have white flowes Figue 9.5- P Geneation (puebed paents) Monohybid Cosses Puple flowes White flowes Mendel developed fou hypotheses fom the monohybid coss, listed hee using moden teminology (including gene instead of heitable facto ).. The altenative vesions of genes ae called alleles. 03 Peason Education, Inc. Figue 9.5- P Geneation (puebed paents) Monohybid Cosses Puple flowes White flowes. Fo each inheited chaacte, an oganism inheits two alleles, one fom each paent. F Geneation All plants have puple flowes An oganism is homozygous fo that gene if both alleles ae identical. An oganism is heteozygous fo that gene if the alleles ae diffeent. 03 Peason Education, Inc.

5 Monohybid Cosses Figue 9.6a 3. If two alleles of an inheited pai diffe, then one detemines the oganism s appeaance and is called the dominant allele and P Geneation Genetic makeup (alleles) the othe has no noticeable effect on the oganism s appeaance and is called the ecessive allele. Alleles caied by paents Puple flowes PP White flowes pp All P All p 03 Peason Education, Inc. Monohybid Cosses Figue 9.6b. cay only one allele fo each inheited chaacte. The two alleles fo a chaacte segegate (sepaate) fom each othe duing the poduction of gametes. This statement is called the law of segegation. F Geneation (hybids) Alleles segegate P Puple flowes All Pp p 03 Peason Education, Inc. Monohybid Cosses Figue 9.6c Do Mendel s hypotheses account fo the 3: atio he obseved in the F geneation? A Punnett squae highlights F Geneation (hybids) Spem fom F plant P p the fou possible combinations of gametes and the fou possible offsping in the F geneation. Eggs fom F plant P p PP Pp Pp pp Phenotypic atio Genotypic atio 3 puple : white PP : Pp : pp 5 03 Peason Education, Inc.

6 Monohybid Cosses Mendel s Law of Independent Assotment Geneticists distinguish between an oganism s physical appeaance and its genetic makeup. An oganism s physical appeaance is its phenotype. An oganism s genetic makeup is its genotype. A dihybid coss is the mating of paental vaieties diffeing in two chaactes. What would esult fom a dihybid coss? Two hypotheses ae possible:. dependent assotment o. independent assotment. 03 Peason Education, Inc. 03 Peason Education, Inc. Genetic Alleles and Homologous Chomosomes A gene locus is a specific location of a gene along a chomosome. Homologous chomosomes have alleles (altenate vesions) of a gene at the same locus. Blast Animation: Two-Tait Cosses Select Play 03 Peason Education, Inc. 03 Peason Education, Inc. Figue 9.7 Figue 9.c Homologous chomosomes Gene loci Dominant allele P a B P Genotype: PP Homozygous fo the dominant allele a aa Homozygous fo the ecessive allele b Bb Recessive allele Heteozygous with one dominant and one ecessive allele 6

7 Figue 9. P Geneation (a) Hypothesis: Dependent assotment RRYY RY y yy (b) Hypothesis: Independent assotment RRYY RY y yy Using a Testcoss to Detemine an Unknown Genotype A testcoss is a mating between F Geneation RYy RYy an individual of dominant phenotype (but unknown genotype) and F Geneation Spem RY y RY RY RRYY Spem Y RYY Ry y RRYy RYy a homozygous ecessive individual. RY Eggs y Eggs Y Ry RYY YY RYy Yy RRYy RYy RRyy Ryy Yellow ound Geen ound Pedicted esults (not actually seen) y RYy Yy Ryy yy Actual esults (suppot hypothesis) Yellow winkled Geen winkled 03 Peason Education, Inc. Mendel s Law of Independent Assotment Figue 9.0 Mendel s dihybid coss suppoted the hypothesis that each pai of alleles segegates independently of the othe pais duing gamete fomation. Testcoss Thus, the inheitance of one chaacte has no effect on the inheitance of anothe. Genotypes B_ bb This is called Mendel s law of independent assotment. Independent assotment is also seen in two heeditay chaactes in Labado etieves. 03 Peason Education, Inc. Two possible genotypes fo the black dog: BB B o Bb b Bb b Bb bb Offsping All black black : chocolate B b Figue 9.9 Blind dog Blind dog The Rules of Pobability Mendel s stong backgound in mathematics helped him undestand pattens of inheitance. Phenotypes Genotypes Black coat, nomal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, nomal vision bbn_ (a) Possible phenotypes of Labado etieves Mating of double heteozygotes (black coat, nomal vision) BbNn BbNn Chocolate coat, blind (PRA) bbnn The ule of multiplication states that the pobability of a compound event is the poduct of the sepaate pobabilities of the independent events. 7 Blind Blind Phenotypic atio of offsping 9 black coat, nomal vision 3 black coat, blind (PRA) 3 chocolate coat, nomal vision chocolate coat, blind (PRA) (b) A Labado dihybid coss 03 Peason Education, Inc.

8 Figue 9. F Genotypes Bb female Bb male Family Pedigees F Genotypes Fomation of eggs Fomation of spem Dominant taits ae not necessaily B Male gametes b nomal o moe common. Wild-type taits ae Female gametes B B B B ( ) b b B b b b those seen most often in natue and not necessaily specified by dominant alleles. 03 Peason Education, Inc. Family Pedigees Family Pedigees Mendel s pinciples apply to the inheitance of many human taits. A family pedigee shows the histoy of a tait in a family and allows geneticists to analyze human taits. 03 Peason Education, Inc. 03 Peason Education, Inc. Figue 9. RECESSIVE TRAITS DOMINANT TRAITS Feckles No feckles Widow s peak Staight hailine Fee ealobe Attached ealobe Figue 9.3 Fist geneation (gandpaents) Second geneation (paents, aunts, and uncles) Thid geneation (bothe and siste) Evelyn FF o Ff Aaon Ff Fed ff Betty Ff Female Male Female Male Attached Fee Gabe Hal ff Ff Kevin ff Cletus ff Ina Ff Lisa FF o Ff Deba Ff Jill ff

9 Figue 9.3a Recessive Disodes Most human genetic disodes ae ecessive. Individuals who have the ecessive allele but appea nomal ae caies of the disode. 03 Peason Education, Inc. Human Disodes Contolled by a Single Gene Many human taits Figue 9. Paents Heaing Dd Heaing Dd show simple inheitance pattens and ae contolled by single genes on autosomes. Offsping D Spem d D Eggs d DD Heaing Dd Heaing (caie) Dd Heaing (caie) dd Deaf 03 Peason Education, Inc. Table 9. Recessive Disodes Cystic fibosis is the most common lethal genetic disease in the United States and caused by a ecessive allele caied by about one in 3 Ameicans Peason Education, Inc.

10 Recessive Disodes Figue 9.6 Polonged geogaphic isolation of cetain populations can lead to inbeeding, the mating of close elatives. Inbeeding inceases the chance of offsping that ae homozygous fo a hamful ecessive tait. Nomal (no achondoplasia) dd Paents d Spem d Dwaf (achondoplasia) Dd Molly Jo Jeemy D Eggs Dd Dwaf Dd Dwaf Jacob Zachay Matt Amy d dd Nomal dd Nomal 03 Peason Education, Inc. Dominant Disodes Some human genetic disodes ae dominant. Achondoplasia is a fom of dwafism. The homozygous dominant genotype causes death of the embyo. Thus, only heteozygotes have this disode. Huntington s disease, which leads to degeneation of the nevous system, does not usually begin until middle age. The Pocess of Science: What Is the Genetic Basis of Coat Vaiation in Dogs? Obsevation: Dogs come in a wide vaiety of physical types. Question: What is the genetic basis fo canine coats? Hypothesis: A compaison of genes of a wide vaiety of dogs with diffeent coats would identify the genes esponsible. 03 Peason Education, Inc. 03 Peason Education, Inc. Figue 9.5 The Pocess of Science: What Is the Genetic Basis of Coat Vaiation in Dogs? Pediction: Mutations in just a few genes account fo the coat appeaance. Expeiment: Compaed DNA sequences of 6 dogs fom dozens of beeds. Results: Thee genes in diffeent combinations poduced seven diffeent coat appeaances, fom vey shot hai to full, thick, wied hai Peason Education, Inc.

11 Figue 9.7 Incomplete Dominance in Plants and People In incomplete dominance, F hybids have an appeaance between the phenotypes of the two paents. 03 Peason Education, Inc. Genetic Testing Today many tests can detect the pesence of disease-causing alleles. Figue 9.- P Geneation Red RR R White Most genetic tests ae pefomed duing pegnancy. Amniocentesis collects cells fom amniotic fluid. Choionic villus sampling emoves cells fom placental tissue. Genetic counseling helps patients undestand the esults and implications of genetic testing. 03 Peason Education, Inc. VARIATIONS ON MENDEL S LAWS Some pattens of genetic inheitance ae not explained by Mendel s laws. Figue 9.- P Geneation Red RR R White F Geneation Pink R R 03 Peason Education, Inc.

12 Figue 9.-3 P Geneation Red RR White Figue 9.9 F Geneation R Pink R GENOTYPE HH Hh hh Heteozygous Homozygous fo ability to make LDL eceptos Homozygous fo inability to make LDL eceptos F Geneation R Eggs R Spem R RR R R PHENOTYPE LDL ecepto LDL Cell Nomal Mild disease Sevee disease Incomplete Dominance in Plants and People Hypecholesteolemia is a human tait that is an example of incomplete dominance and is chaacteized by dangeously high levels of cholesteol in the blood. ABO Blood Goups: An Example of Multiple Alleles and Codominance The ABO blood goups in humans ae an example of multiple alleles. The immune system poduces blood poteins called antibodies that bind specifically to foeign cabohydates. 03 Peason Education, Inc. 03 Peason Education, Inc. Incomplete Dominance in Plants and People In hypecholesteolemia, heteozygotes have blood cholesteol levels about twice nomal, and homozygotes have about five times the nomal amount of blood cholesteol and may have heat attacks as ealy as age. ABO Blood Goups: An Example of Multiple Alleles and Codominance If a dono s blood cells have a cabohydate (A o B) that is foeign to the ecipient, the blood cells may clump togethe, potentially killing the ecipient. The clumping eaction is the basis of a bloodtyping lab test. The human blood type alleles I A and I B ae codominant, meaning that both alleles ae expessed in heteozygous individuals who have type AB blood. 03 Peason Education, Inc. 03 Peason Education, Inc.

13 Figue 9.0a Blood Goup (Phenotype) Genotypes A B I A I A o I A i I B I B o I B i Red Blood Cells Cabohydate A Cabohydate B Antibodies Pesent in Blood Anti-B Anti-A Pleiotopy and Sickle-Cell Disease Pleiotopy is when one gene influences seveal chaactes. Sickle-cell disease exhibits pleiotopy, esults in abnomal hemoglobin poteins, and AB I A I B causes disk-shaped ed blood cells to defom into a sickle shape with jagged edges. O ii Anti-A Anti-B 03 Peason Education, Inc. Figue 9.0c Figue 9. Individual homozygous fo sickle-cell allele Sickle-cell (abnomal) hemoglobin Abnomal hemoglobin cystallizes into long flexible chains, causing ed blood cells to become sickle-shaped. Coloized SEM Sickled cells can lead to a cascade of symptoms, such as weakness, pain, ogan damage, and paalysis. Figue 9.0b Blood Goup (Phenotype) A Reactions When Blood fom Goups Below Is Mixed with Antibodies fom Goups at Left O A B AB Polygenic Inheitance Polygenic inheitance is the additive effects of two o moe genes on a single phenotype. B AB 3 O 03 Peason Education, Inc.

14 Figue 9.a The Role of Envionment P Geneation aabbcc (vey shot) AABBCC (vey tall) shot allele tall allele Many human chaactes esult fom a combination of heedity and envionment. F Geneation Only genetic influences ae inheited. AaBbCc (medium height) AaBbCc (medium height) 03 Peason Education, Inc. Figue 9.b Figue 9.3 F Geneation shot allele tall allele Figue 9.c Faction of population THE CHROMOSOMAL BASIS OF INHERITANCE The chomosome theoy of inheitance states that genes ae located at specific positions (loci) on chomosomes and the behavio of chomosomes duing meiosis and fetilization accounts fo inheitance pattens. 6 Vey shot Adult height Vey tall 03 Peason Education, Inc.

15 THE CHROMOSOMAL BASIS OF INHERITANCE It is chomosomes that Figue 9.5- Dihybid testcoss Gay body, long wings (wild-type) Black body, shot wings (mutant) undego segegation and independent assotment duing meiosis and account fo Mendel s laws. GgLl Female Results Offsping ggll Male Gay-long GgLl Black-shot ggll Gay-shot Ggll Black-long ggll Peason Education, Inc. Paental phenotypes 3% Recombinant phenotypes 7% Figue 9. P Geneation Round-yellow Winkled-geen seeds seeds Y y (RRYY) (yy) R Y R y MEIOSIS FERTILIZATION R Y y F Geneation All ound-yellow R seeds y (RYy) Law of Segegation: Follow the long Law of Independent Assotment: Y chomosomes (caying R and ) taking Follow both the long and the shot eithe the left o ight banch. chomosomes. R MEIOSIS R They ae aanged in eithe of Metaphase I two equally likely ways at Y y (altenative Y y The R and alleles segegate in metaphase I. aangements) anaphase I of meiosis. R R Metaphase Only one long II They sot independently, Y y Y y chomosome ends giving fou gamete types. up in each gamete. y Y Y y Y Y y y R R R R Genetic Recombination: Cossing Ove Cossing ove can sepaate linked alleles, poduce gametes with ecombinant gametes, and poduce offsping with ecombinant phenotypes. The pecentage of ecombinant offsping among the total is called the ecombination fequency. RY y Y Ry FERTILIZATION AMONG THE F Fetilization ecombines the PLANTS Fetilization esults in the 9:3:3: and R alleles at andom. phenotypic atio in the F geneation. F Geneation 9 : 3 : 3 : 03 Peason Education, Inc. Linked Genes Figue 9.6 Linked genes ae located close togethe on a chomosome and A B a b tend to be inheited togethe. A B Thomas Hunt Mogan used the fuit fly Dosophila melanogaste and detemined that some genes wee linked based on the inheitance pattens of thei taits. ab Pai of homologous chomosomes Cossing ove Paental gametes A b a B Recombinant gametes 5 03 Peason Education, Inc.

16 Figue 9.7 GgLl (female) G L g l CROSSING OVER g l g l ggll (male) SEX CHROMOSOMES AND SEX-LINKED GENES Sex chomosomes influence the inheitance of cetain taits. Fo example, humans that have a pai of sex chomosomes designated G L g l G l g L g l X and Y ae male o Spem Paental gametes Recombinant gametes Eggs FERTILIZATION X and X ae female. Offsping G L g l g l G l g L g l g l g l Paental Recombinant 03 Peason Education, Inc. Linkage Maps Figue 9.9 Ealy studies of cossing ove wee pefomed using the fuit fly Dosophila melanogaste. Y X Male XY Somatic cells Female XX Alfed H. Stutevant, a student of Mogan, developed a method fo mapping the elative gene locations, which esulted in the ceation of linkage maps. Coloized SEM X Y Spem Egg X XX Offsping XY Female Male 03 Peason Education, Inc. Figue 9. Sex Detemination in Humans Chomosome g c l Nealy all mammals have a pai of sex chomosomes designated X and Y. Males have an X and Y. 7% Females have XX. 9% Recombination fequencies 9.5% 6 03 Peason Education, Inc.

17 Sex-Linked Genes Figue 9.3b Any gene located on a sex chomosome is called a sex-linked gene. Most sex-linked genes ae found on the X chomosome. Red-geen coloblindness is a common human sex-linked disode and caused by a malfunction of light-sensitive cells in the eyes. Key Unaffected individual Caie Coloblind individual Eggs X N X n X N X n X N Y X N Y Spem X N X N X N Y X N X n X n Y (b) Caie female nomal male 03 Peason Education, Inc. Figue 9.30 Figue 9.3c X N X n X n Y Key Unaffected individual Caie Coloblind individual Eggs X N X n X N X n Y X N Y Spem X n X n X n X n Y (c) Caie female coloblind male Figue 9.3a Sex-Linked Genes X N X N X n Y Hemophilia Key Unaffected individual Caie Coloblind individual Eggs X N X N X n X N X n X N X n Y X N Y X N Y Spem is a sex-linked ecessive blood-clotting tait that may esult in excessive bleeding and death afte elatively mino cuts and buises and has plagued the oyal families of Euope. 7 (a) Nomal female coloblind male 03 Peason Education, Inc.

18 Figue 9.3 Figue 9.33 Queen Victoia Alice Albet Louis Ancestal canine Wolf Chinese sha-pei Akita Sibeian husky Alexanda Cza Nicholas II of Russia Basenji Alaskan malamute Afghan hound Alexis Saluki Rottweile Sheepdog Retieve Evolution Connection: Baking Up the Evolutionay Tee About 5,000 yeas ago in East Asia, people began to cohabit with ancestal canines that wee pedecessos of moden wolves and dogs. As people settled into geogaphically distinct populations, diffeent canines became sepaated and eventually became inbed. 03 Peason Education, Inc. Evolution Connection: Baking Up the Evolutionay Tee A 00 study indicated that small dogs wee developed within the fist pemanent agicultual settlements of the Middle East aound,000 yeas ago. Continued ove millennia, genetic tinkeing has esulted in a divese aay of dog body types and behavios. 03 Peason Education, Inc.