CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 12 The Chromosomal Basis of Inheritance

© 2014 Pearson Education, Inc. Figure 12.1

© 2014 Pearson Education, Inc. Fig , p.197 chimpanzee human gorillaorangutan Chromosome Structure

© 2014 Pearson Education, Inc. Figure 12.2a P Generation Gametes Yellow-round seeds (YYRR) Meiosis Fertilization Green-wrinkled seeds (yyrr) R R Y Y Y R r y y y r r

© 2014 Pearson Education, Inc. F 1 Generation LAW OF SEGREGATION The two alleles for each gene separate. All F 1 plants produce yellow-round seeds (YyRr). LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently. Meiosis Metaphase I Anaphase I Metaphase II R R 1 4  yR 1 4  1 4  1 4  Yr yr YR y y y Y r r r Y y y r Y R R Y Y y R r r Y R Rr y Y Y R y r Y R y r y r R Y R R YY y r r y Figure 12.2b

© 2014 Pearson Education, Inc. LAW OF SEGREGATION LAW OF INDEPENDENT ASSORTMENT F 2 Generation Fertilization recombines the R and r alleles at random. 9 : 3 : 1 An F 1  F 1 cross-fertilization Fertilization results in the 9:3:3:1 phenotypic ratio in the F 2 generation. 33 Figure 12.2c

© 2014 Pearson Education, Inc. Thomas Morgan Worked with fruit flies Reciprocal crosses - 2 crosses where the trait of each sex is reversed Example - 1- White eyed male X Red eyed female 2- White eyed Female X Red eyed male

© 2014 Pearson Education, Inc. recessive male X Y X X X all red- eyed F 1 offspring X Y X X X 1/2 1/4 gametes White-eyed males show up in F 2 generation Fig. 12-9, p.193 Thomas Morgan

© 2014 Pearson Education, Inc. Fig. 12-9, p.193

© 2014 Pearson Education, Inc. King Charles II Of Spain

© 2014 Pearson Education, Inc.

Fig b,p.200

© 2014 Pearson Education, Inc. The Y Chromosome  Fewer than two dozen genes identified  SRY gene (sex-determining region of Y) is the master gene for male sex determination

© 2014 Pearson Education, Inc. The X Chromosome  Carries more than 2,300 genes  Most for nonsexual traits  Genes on X chromosome can be expressed in both sexes

© 2014 Pearson Education, Inc. Figure 12.5 X Y

© 2014 Pearson Education, Inc.  gene on either sex chromosome is called a sex- linked gene

© 2014 Pearson Education, Inc. Figure 12.7 XNXNXNXN XnYXnY Y XnXn XNXN XNXN XNXnXNXn XNXnXNXn XNYXNY XNYXNY Eggs (a) Sperm Eggs (c)(b) XNYXNY XNXnXNXn XNXnXNXn XnYXnY XnXn Y XNXN XnXn XNXnXNXn XnXnXnXn XnYXnY XNYXNY XNXN XnXn XNXN Y XNXNXNXN XnYXnY XNXnXNXn XNYXNY

© 2014 Pearson Education, Inc.  Some disorders caused by recessive alleles on the X chromosome in humans  Color blindness (mostly X-linked)  Duchenne muscular dystrophy  Hemophilia

© 2014 Pearson Education, Inc. Fig , p.195 Color Blindness

© 2014 Pearson Education, Inc. Fig , p.195 Color Blindness

© 2014 Pearson Education, Inc. Fig , p.194 Hemophilia

© 2014 Pearson Education, Inc. X Chromosome Inactivation  One X inactivated in each cell of female mammals (Paternal X in Marsupials, random in Placentals)  The inactive X condenses into a Barr body  Creates “mosaic” for X chromosomes  Governed by XIST gene  Dosage compensation theory - shutdown prevents “overdose” of gene products in females

© 2014 Pearson Education, Inc. Fig. 15-4a, p.234 X Chromosome Inactivation

© 2014 Pearson Education, Inc. Fig. 15-5, p.234 X Chromosome Inactivation

© 2014 Pearson Education, Inc. Figure 12.8 Early embryo: Two cell populations in adult cat: X chromosomes Cell division and X chromosome inactivation Allele for orange fur Allele for black fur Active X Orange furBlack fur Inactive X Active X

© 2014 Pearson Education, Inc.  Genes located on the same chromosome are called linked genes  Degree of linkage varies with distance between loci Concept 12.3: Linked genes tend to be inherited together because they are located near each other on the same chromosome

© 2014 Pearson Education, Inc. Crossover Frequency Proportional to the distance that separates genes ABCD Crossing over will disrupt linkage between A and B more often than C and D In-text figure Page 178

© 2014 Pearson Education, Inc. Full Linkage x ABab 50% AB50% ab All AaBb meiosis, gamete formation Parents: F 1 offspring: Equal ratios of two types of gametes: A B a b A B a b a b A B Figure Page 178

© 2014 Pearson Education, Inc. Incomplete Linkage Parents: F 1 offspring: Unequal ratios of four types of gametes: All AaCc x meiosis, gamete formation ACac A C A C A C a c a c A c a C a c parental genotypes recombinant genotypes Figure Page 178

© 2014 Pearson Education, Inc. Figure 12.UN01 F 1 dihybrid female and homozygous recessive male in testcross Most offspring b  vg  b vg b  vg  or

© 2014 Pearson Education, Inc. Figure 12.10b b  vg + b vg b  vg + b vg b  vg + b  vg b vg  b vg Meiosis I Meiosis I and II Meiosis II Eggs b vg b vg + b + vgb + vg + Sperm Wild-type F 1 dihybrid (gray body, normal wings) F 1 dihybrid testcross Recombinant chromosomes Homozygous recessive (black body, vestigial wings)

© 2014 Pearson Education, Inc. Figure 12.10c b  vg + b vg b vg  b  vg Recombinant chromosomes Eggs 185 Black- normal 206 Gray- vestigial 944 Black- vestigial 965 Wild type (gray-normal) Testcross offspring Sperm b vg b vg  b  vg b vg b  vg  b vg Parental-type offspring Recombinant offspring Recombination frequency   100  17% 2,300 total offspring 391 recombinants

© 2014 Pearson Education, Inc.  A linkage map - genetic map of chromosome based on recombination frequencies  Distances expressed as map units; one map unit represents a 1% recombination frequency

© 2014 Pearson Education, Inc. Figure Recombination frequencies Results Chromosome bcnvg 17% 9.5%9%

© 2014 Pearson Education, Inc. Figure Short aristae Black body Cinnabar eyes Vestigial wings Brown eyes Red eyes Normal wings Red eyes Gray body Long aristae (appendages on head) Wild-type phenotypes Mutant phenotypes

© 2014 Pearson Education, Inc. Abnormal Chromosome Number  nondisjunction, pairs of homologous chromosomes do not separate during meiosis  result, - one gamete carries extra chromosome, and another gamete receives none Video: Nondisjunction

© 2014 Pearson Education, Inc. Figure Meiosis I Nondisjunction

© 2014 Pearson Education, Inc. Figure Meiosis I Nondisjunction Meiosis II Non- disjunction

© 2014 Pearson Education, Inc. Figure Meiosis I Nondisjunction Meiosis II Non- disjunction Gametes Number of chromosomes Nondisjunction of homo- logous chromosomes in meiosis I (a)(b) Nondisjunction of sister chromatids in meiosis II n  1 n − 1 nn

© 2014 Pearson Education, Inc.  Aneuploidy results from fertilization of gametes in which nondisjunction occurred  Offspring with this condition have an abnormal number of a particular chromosome

© 2014 Pearson Education, Inc.  A monosomic zygote has only 1 copy of a particular chromosome  A trisomic zygote has three copies of a particular chromosome

© 2014 Pearson Education, Inc.  Polyploidy organism has more than two sets of chromosomes  Triploidy (3n)  Tetraploidy (4n) …  Polyploidy is common in plants, but not animals

© 2014 Pearson Education, Inc. Alterations of Chromosome Structure  Breakage of a chromosome can lead to four types of changes in chromosome structure  Deletion removes a chromosomal segment  Duplication repeats a segment  Inversion reverses orientation of a segment within a chromosome  Translocation moves a segment from one chromosome to another

© 2014 Pearson Education, Inc. Figure 12.14a (a) Deletion A deletion removes a chromosomal segment. (b) Duplication A duplication repeats a segment.

© 2014 Pearson Education, Inc. Figure 12.14b (c) Inversion (d) Translocation An inversion reverses a segment within a chromosome. A translocation moves a segment from one chromosome to a nonhomologous chromosome.

© 2014 Pearson Education, Inc. Down Syndrome (Trisomy 21)  Down syndrome 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 age of the mother, a correlation that has not been explained

© 2014 Pearson Education, Inc. Figure 12.15

© 2014 Pearson Education, Inc. Fig , p.199 Down Syndrome

© 2014 Pearson Education, Inc. Aneuploidy of Sex Chromosomes  Nondisjunction of sex chromosomes produces a variety of aneuploid conditions  Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals  Females with trisomy X (XXX) have no unusual physical features except being slightly taller than average

© 2014 Pearson Education, Inc.  Monosomy X, called Turner syndrome, produces X0 females,  It is the only known viable monosomy in humans

© 2014 Pearson Education, Inc. Disorders Caused by Structurally Altered Chromosomes  The syndrome cri du chat (“cry of the cat”) results from a specific deletion in chromosome 5  A child born with this syndrome is mentally disabled and has a catlike cry; individuals usually die in infancy or early childhood

© 2014 Pearson Education, Inc. Deletion  Cri-du-chat Fig , p.196

© 2014 Pearson Education, Inc. Disorders Caused by Structurally Altered Chromosomes  Certain cancers, including chronic myelogenous leukemia (CML), are caused by translocations of chromosomes

© 2014 Pearson Education, Inc. Figure Normal chromosome 9 Normal chromosome 22 Reciprocal translocation Translocated chromosome 9 Translocated chromosome 22 (Philadelphia chromosome)

© 2014 Pearson Education, Inc.