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Download AP Biology Chapter 15 Chromosomal Basis of Inheritance Guided
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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 15 The Chromosomal Basis of Inheritance Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: Locating Genes Along Chromosomes • Mendel’s “hereditary factors” were __________ • Today we can show that genes are located on _____________________ • The location of a particular gene can be seen by tagging isolated chromosomes with a ______________________ that highlights the gene © 2011 Pearson Education, Inc. Figure 15.1 Concept 15.1: Mendelian inheritance has its physical basis in the behavior of chromosomes • Mitosis and meiosis were first described in the _______________ • The _____________________________ states: – Mendelian genes have specific ________ (positions) on chromosomes – Chromosomes undergo _______________ and ___________________________ • The behavior of chromosomes during ___________ can account for Mendel’s laws of segregation and independent assortment © 2011 Pearson Education, Inc. Figure 15.2a P Generation Yellow-round seeds (YYRR) Y Y R R r y y r Meiosis Fertilization Gametes R Y y r Green-wrinkled seeds (yyrr) Figure 15.2b All F1 plants produce yellow-round seeds (YyRr). F1 Generation R y r R y r Y Y LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation. Meiosis LAW OF SEGREGATION The two alleles for each gene separate during gamete formation. r R Y y r R Metaphase I y Y 1 1 R r r R Y y Anaphase I Y y r R 2 y Y Y R R 1/ 4 YR r 1/ 4 yr y Y Y Y y r R 2 y Y Gametes r Metaphase II r r 1/ 4 Yr y y R R 1/ 4 yR Figure 15.2c LAW OF INDEPENDENT ASSORTMENT LAW OF SEGREGATION F2 Generation 3 Fertilization recombines the R and r alleles at random. An F1 F1 cross-fertilization 9 :3 :3 :1 3 Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. Morgan’s Experimental Evidence: Scientific Inquiry • The first solid evidence associating a specific gene with a specific chromosome came from ___________________, an embryologist • Morgan’s experiments with _______________ provided convincing evidence that chromosomes are the location of Mendel’s heritable factors © 2011 Pearson Education, Inc. Morgan’s Choice of Experimental Organism • Several characteristics make fruit flies a convenient organism for genetic studies – They produce _____________________ – A generation can be bred every _____________ – They have only _____________ of chromosomes © 2011 Pearson Education, Inc. • Morgan noted _____________, or normal, phenotypes that were common in the fly populations • Traits alternative to the wild type are called _______________ phenotypes © 2011 Pearson Education, Inc. Figure 15.3 Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair • In one experiment, Morgan mated male flies with white eyes (_______) with female flies with red eyes (_____________) – The F1 generation all had ____________ – The F2 generation showed the _____ red:white eye ratio, but only ___________ had white eyes • Morgan determined that the white-eyed mutant allele must be located on the ___ chromosome • Morgan’s finding supported the chromosome theory of inheritance © 2011 Pearson Education, Inc. Figure 15.4a EXPERIMENT P Generation F1 Generation RESULTS F2 Generation All offspring had red eyes. Figure 15.4b CONCLUSION P Generation X X w X Y w w Eggs F1 Generation Sperm w w w w w Eggs F2 Generation w w w Sperm w w w w w w Concept 15.2: Sex-linked genes exhibit unique patterns of inheritance • In humans and some other animals, there is a chromosomal basis of ______________________ © 2011 Pearson Education, Inc. The Chromosomal Basis of Sex • In humans and other mammals, there are two varieties of sex chromosomes: a larger ____ chromosome and a smaller __ chromosome • Only the ________________________ have regions that are homologous with corresponding regions of the X chromosome • The ________________ on the Y chromosome codes for a protein that directs the development of male anatomical features © 2011 Pearson Education, Inc. Figure 15.5 X Y • Females are ____, and males are _______ • Each ovum contains an ___ chromosome, while a sperm may contain either an __ or a ___ chromosome • Other animals have different methods of sex determination © 2011 Pearson Education, Inc. Figure 15.6 44 XY 44 XX Parents 22 22 X or Y 22 X Sperm Egg 44 XX or 44 XY (a) The X-Y system Zygotes (offspring) 22 XX 22 X 76 ZW 76 ZZ 32 (Diploid) 16 (Haploid) (b) The X-0 system (c) The Z-W system (d) The haplo-diploid system • A gene that is located on either sex chromosome is called a ________________ • Genes on the Y chromosome are called ________________; there are few of these • Genes on the X chromosome are called ___________________ © 2011 Pearson Education, Inc. Inheritance of X-Linked Genes • X chromosomes have genes for many characters unrelated to sex, whereas the Y chromosome mainly encodes genes related to ____________________ © 2011 Pearson Education, Inc. • ___________________ follow specific patterns of inheritance • For a recessive ______________ to be expressed – A female needs ________________ of the allele (homozygous) – A male needs only _______________ of the allele (hemizygous) • X-linked recessive disorders are much more common in _____________ than in females © 2011 Pearson Education, Inc. Figure 15.7 XNXN Sperm Xn XNXn XnY Sperm XN Y XNY XNXn Sperm Xn Y XnY Y Eggs XN XNXn XNY Eggs XN XNXN XNY Eggs XN XNXn XNY XN XNXn XNY Xn XNXn XnY Xn XnXn XnY (a) (b) (c) • Some disorders caused by recessive alleles on the X chromosome in humans – ___________________ (mostly X-linked) – ____________________________ – ________________________ © 2011 Pearson Education, Inc. X Inactivation in Female Mammals • In mammalian females, one of the two X chromosomes in each cell is ______________ _____________ during embryonic development • The inactive X condenses into a ____________ • If a female is heterozygous for a particular gene located on the X chromosome, she will be _______________ for that character © 2011 Pearson Education, Inc. Figure 15.8 X chromosomes Allele for orange fur Early embryo: Two cell populations in adult cat: Allele for black fur Cell division and X chromosome inactivation Active X Inactive X Active X Black fur Orange fur Concept 15.3: Linked genes tend to be inherited together because they are located near each other on the same chromosome • Each chromosome has ________________ _______________ of genes (except the Y chromosome) • Genes located on the same chromosome that tend to be inherited together are called ________________ © 2011 Pearson Education, Inc. How Linkage Affects Inheritance • Morgan did other experiments with fruit flies to see how linkage affects inheritance of two characters • Morgan crossed flies that differed in traits of ______________________________ © 2011 Pearson Education, Inc. Figure 15.9-1 EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg Figure 15.9-2 EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg F1 dihybrid (wild type) b b vg vg TESTCROSS Double mutant b b vg vg Figure 15.9-3 EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg F1 dihybrid (wild type) Double mutant TESTCROSS b b vg vg b b vg vg Testcross offspring Eggs b vg b vg Wild type Black(gray-normal) vestigial b vg Grayvestigial b vg Blacknormal b vg Sperm b b vg vg b b vg vg b b vg vg b b vg vg Figure 15.9-4 EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b b vg vg b b vg vg F1 dihybrid (wild type) Double mutant TESTCROSS b b vg vg b b vg vg Testcross offspring Eggs b vg b vg b vg Wild type Black(gray-normal) vestigial b vg Blacknormal Grayvestigial b vg Sperm b b vg vg b b vg vg b b vg vg b b vg vg PREDICTED RATIOS If genes are located on different chromosomes: 1 : 1 : 1 : 1 If genes are located on the same chromosome and parental alleles are always inherited together: 1 : 1 : 0 : 0 965 : 944 : 206 : 185 RESULTS • Morgan found that body color and wing size are usually inherited _____________ in specific combinations (________________________) • He noted that these genes do not assort independently, and reasoned that they were on the ______________________________ © 2011 Pearson Education, Inc. Figure 15.UN01 F1 dihybrid female and homozygous recessive male in testcross b+ vg+ b vg b vg b vg b+ vg+ b vg Most offspring or b vg b vg • However, ________________ were also produced • Understanding this result involves exploring ________________________________, the production of offspring with combinations of traits differing from either parent © 2011 Pearson Education, Inc. Genetic Recombination and Linkage • The genetic findings of Mendel and Morgan relate to the chromosomal basis of ______________________ © 2011 Pearson Education, Inc. Recombination of Unlinked Genes: Independent Assortment of Chromosomes • Mendel observed that combinations of traits in some offspring __________ from either parent • Offspring with a phenotype matching one of the parental phenotypes are called ______________ • Offspring with nonparental phenotypes (new combinations of traits) are called ____________ _________________________________ • A ____________ frequency of recombination is observed for any two genes on different chromosomes © 2011 Pearson Education, Inc. Figure 15.UN02 Gametes from yellow-round dihybrid parent (YyRr) Gametes from greenwrinkled homozygous recessive parent (yyrr) YR yr Yr yR YyRr yyrr Yyrr yyRr yr Parentaltype offspring Recombinant offspring Recombination of Linked Genes: Crossing Over • Morgan discovered that genes can be linked, but the linkage was ______________, because some recombinant phenotypes were observed • He proposed that some process must occasionally break the physical connection between genes on the same chromosome • That mechanism was the ________________ of homologous chromosomes © 2011 Pearson Education, Inc. Animation: Crossing Over Right-click slide / select”Play” © 2011 Pearson Education, Inc. Figure 15.10a Gray body, normal wings (F1 dihybrid) Testcross parents Black body, vestigial wings (double mutant) b vg b vg b vg b vg Replication of chromosomes Replication of chromosomes Meiosis I b vg b vg b vg b vg b vg b vg b vg b vg b vg Meiosis I and II b vg b vg b vg Meiosis II bvg Eggs Recombinant chromosomes b vg b vg b vg b vg Sperm Figure 15.10b Recombinant chromosomes Eggs Testcross offspring bvg 965 Wild type (gray-normal) b vg b vg b vg 944 Blackvestigial 206 Grayvestigial 185 Blacknormal b vg b vg b vg b vg b vg b vg b vg b vg Parental-type offspring Recombinant offspring Recombination 391 recombinants 100 17% frequency 2,300 total offspring b vg Sperm New Combinations of Alleles: Variation for Normal Selection • ____________________ chromosomes bring alleles together in new combinations in gametes • _____________________ increases even further the number of variant combinations that can be produced • This abundance of genetic variation is the raw material upon which ____________________ works © 2011 Pearson Education, Inc. Mapping the Distance Between Genes Using Recombination Data: Scientific Inquiry • Alfred Sturtevant, one of Morgan’s students, constructed a _______________, an ordered list of the genetic loci along a particular chromosome • Sturtevant predicted that the farther apart two genes are, the higher the probability that a ___________________ will occur between them and therefore the higher the recombination frequency © 2011 Pearson Education, Inc. • A _________________ is a genetic map of a chromosome based on recombination frequencies • Distances between genes can be expressed as _____________; one map unit, or centimorgan, represents a 1% recombination frequency • Map units indicate _____________________, not precise locations of genes © 2011 Pearson Education, Inc. Figure 15.11 RESULTS Recombination frequencies 9% Chromosome 9.5% 17% b cn vg • Genes that are far apart on the same chromosome can have a recombination frequency near _________ • Such genes are ______________ linked, but _______________ unlinked, and behave as if found on different chromosomes © 2011 Pearson Education, Inc. • Sturtevant used recombination frequencies to make linkage maps of fruit fly genes • Using methods like ____________________, geneticists can develop cytogenetic maps of chromosomes • _________________________ indicate the positions of genes with respect to chromosomal features © 2011 Pearson Education, Inc. Figure 15.12 Mutant phenotypes Short aristae 0 Long aristae (appendages on head) Black body Cinnabar Vestigial eyes wings 48.5 57.5 Gray body Red eyes Brown eyes 67.0 104.5 Normal wings Red eyes Wild-type phenotypes Concept 15.4: Alterations of chromosome number or structure cause some genetic disorders • Large-scale chromosomal alterations in humans and other mammals often lead to ______________________ (miscarriages) or cause a variety of _____________________ • ____________ tolerate such genetic changes better than animals do © 2011 Pearson Education, Inc. Abnormal Chromosome Number • In ______________, pairs of homologous chromosomes do not separate normally during meiosis • As a result, one gamete receives ______ ____________________ of chromosome, and another gamete receives __________ © 2011 Pearson Education, Inc. Figure 15.13-1 Meiosis I Nondisjunction Figure 15.13-2 Meiosis I Nondisjunction Meiosis II Nondisjunction Figure 15.13-3 Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n1 n1 n1 n1 n1 n1 n n Number of chromosomes (a) Nondisjunction of homologous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II • ________________ results from the fertilization of gametes in which nondisjunction occurred • Offspring with this condition have an __________________________ of a particular chromosome © 2011 Pearson Education, Inc. • A ___________ zygote has only one copy of a particular chromosome • A ____________ zygote has three copies of a particular chromosome © 2011 Pearson Education, Inc. • ______________ is a condition in which an organism has more than two complete sets of chromosomes – ___________ (3n) is three sets of chromosomes – ___________ (4n) is four sets of chromosomes • Polyploidy is common in _________, but not animals • ____________ are more normal in appearance than ____________________ © 2011 Pearson Education, Inc. Alterations of Chromosome Structure • Breakage of a chromosome can lead to four types of changes in chromosome structure – __________ removes a chromosomal segment – ____________ repeats a segment – ______________ reverses orientation of a segment within a chromosome – ________________ moves a segment from one chromosome to another © 2011 Pearson Education, Inc. Figure 15.14a (a) Deletion A B C D E F G H A deletion removes a chromosomal segment. A B C E F G H (b) Duplication A B C D E F G H A duplication repeats a segment. A B C B C D E F G H Figure 15.14b (c) Inversion A B C D E F G H An inversion reverses a segment within a chromosome. A D C B E F G H (d) Translocation A B C D E F G H M N O P Q R A translocation moves a segment from one chromosome to a nonhomologous chromosome. M N O C D E F G H A B P Q R Human Disorders Due to Chromosomal Alterations • Alterations of chromosome number and structure are associated with some serious disorders • Some types of ____________ appear to upset the genetic balance less than others, resulting in individuals surviving to birth and beyond • These surviving individuals have a set of symptoms, or ______________, characteristic of the type of aneuploidy © 2011 Pearson Education, Inc. Down Syndrome (Trisomy 21) • ____________________ is an aneuploid condition that results from three copies of chromosome 21 • It affects about one out of every 700 children born in the United States • The frequency of Down syndrome increases with the ________________________, a correlation that has not been explained © 2011 Pearson Education, Inc. Figure 15.15 Figure 15.15a Figure 15.15b Aneuploidy of Sex Chromosomes • Nondisjunction of __________________ produces a variety of aneuploid conditions • _____________________ is the result of an extra chromosome in a male, producing _____ individuals • _______________, called ________________, produces X0 females, who are___________; it is the only known viable monosomy in humans © 2011 Pearson Education, Inc. Disorders Caused by Structurally Altered Chromosomes • The syndrome __________ (“cry of the cat”), results from a specific deletion in ____________________ • A child born with this syndrome is mentally retarded and has a catlike cry; individuals usually die in infancy or early childhood • Certain cancers, including ____________ ______________________ (CML), are caused by translocations of chromosomes © 2011 Pearson Education, Inc. Figure 15.16 Normal chromosome 9 Normal chromosome 22 Reciprocal translocation Translocated chromosome 9 Translocated chromosome 22 (Philadelphia chromosome) Concept 15.5: Some inheritance patterns are exceptions to standard Mendelian inheritance • There are two normal exceptions to Mendelian genetics • One exception involves genes located in the ____________, and the other exception involves genes located outside the _________ • In both cases, the _____________________ contributing an allele is a factor in the pattern of inheritance © 2011 Pearson Education, Inc. Genomic Imprinting • For a few mammalian traits, the phenotype depends on _____________ passed along the alleles for those traits • Such variation in phenotype is called ______________________ • Genomic imprinting involves the silencing of certain genes that are “ ____________” with an imprint during gamete production © 2011 Pearson Education, Inc. Figure 15.17a Paternal chromosome Maternal chromosome Normal Igf2 allele is expressed. Normal Igf2 allele is not expressed. (a) Homozygote Normal-sized mouse (wild type) Figure 15.17b Mutant Igf2 allele inherited from mother Mutant Igf2 allele inherited from father Normal-sized mouse (wild type) Dwarf mouse (mutant) Normal Igf2 allele is expressed. Mutant Igf2 allele is expressed. Mutant Igf2 allele is not expressed. Normal Igf2 allele is not expressed. (b) Heterozygotes • It appears that imprinting is the result of the ________________ (addition of —CH3) of _______________ nucleotides • Genomic imprinting is thought to affect only a _____________________ of mammalian genes • Most imprinted genes are critical for ________________________________ © 2011 Pearson Education, Inc. Inheritance of Organelle Genes • ______________________ (or cytoplasmic genes) are found in organelles in the cytoplasm • ________________________, and other ______ ___ carry small ___________ molecules • Extranuclear genes are inherited ____________ because the zygote’s cytoplasm comes from the egg • The first evidence of extranuclear genes came from studies on the inheritance of yellow or white patches on leaves of an otherwise green plant © 2011 Pearson Education, Inc. Figure 15.18 • Some defects in ___________________ prevent cells from making enough ATP and result in diseases that affect the muscular and nervous systems – For example, mitochondrial myopathy and Leber’s hereditary optic neuropathy © 2011 Pearson Education, Inc.