Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 15 The Chromosomal Basis of Inheritance

Overview: Locating Genes Along Chromosomes Mendel’s “hereditary factors” were genes, though this wasn’t known at the time Today we can show that genes are located on chromosomes The location of a particular gene can be seen by tagging isolated chromosomes with a fluorescent dye that highlights the gene Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Concept 15.1: Mendelian inheritance has its physical basis in the behavior of chromosomes Mitosis and meiosis were first described in the late 1800s The chromosome theory of inheritance states: – Mendelian genes have specific loci (positions) on chromosomes – Chromosomes undergo segregation and independent assortment The behavior of chromosomes during meiosis was said to account for Mendel’s laws of segregation and independent assortment Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig. 15-4a EXPERIMENT P Generation F1F1 All offspring had red eyes 

Fig. 15-4b RESULTS Generation F2F2

Fig EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings ) Double mutant (black body, vestigial wings)  b b vg vg b + b + vg + vg +

Fig EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings ) Double mutant (black body, vestigial wings)  b b vg vg Double mutant TESTCROSS  b + b + vg + vg + F 1 dihybrid (wild type) b + b vg + vg

Fig EXPERIMENT P Generation (homozygous) Wild type (gray body, normal wings ) Double mutant (black body, vestigial wings)  b b vg vg Double mutant TESTCROSS  b + b + vg + vg + F 1 dihybrid (wild type) b + b vg + vg Testcross offspring Eggs b + vg + b vg b + vg b vg + Black- normal Gray- vestigial Black- vestigial Wild type (gray-normal) b vg Sperm b + b vg + vg b b vg vg b + b vg vg b b vg + vg

Fig EXPERIMENT P Generation (homozygous) RESULTS Wild type (gray body, normal wings ) Double mutant (black body, vestigial wings)  b b vg vg Double mutant TESTCROSS  b + b + vg + vg + F 1 dihybrid (wild type) b + b vg + vg Testcross offspring Eggs b + vg + b vg b + vg b vg + Black- normal Gray- vestigial Black- vestigial Wild type (gray-normal) 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: If genes are located on the same chromosome and parental alleles are always inherited together: : : : : : : : : :

Morgan found that body color and wing size are usually inherited together in specific combinations (parental phenotypes) He noted that these genes do not assort independently, and reasoned that they were on the same chromosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Genetic Recombination and Linkage The genetic findings of Mendel and Morgan relate to the chromosomal basis of recombination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig Testcross parents Replication of chromo- somes Gray body, normal wings (F 1 dihybrid) Black body, vestigial wings (double mutant) Replication of chromo- somes b + vg + b vg b + vg + b + vg b vg + b vg Recombinant chromosomes Meiosis I and II Meiosis I Meiosis II b vg + b + vg b vg b + vg + Eggs Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal b + vg + b vg b + vg b vg b vg + Sperm b vg Parental-type offspringRecombinant offspring Recombination frequency = 391 recombinants 2,300 total offspring  100 = 17%

Fig a Testcross parents Replication of chromo- somes Gray body, normal wings (F 1 dihybrid) Black body, vestigial wings (double mutant) Replication of chromo- somes b + vg + b vg b + vg + b + vg b vg + b vg Recombinant chromosomes Meiosis I and II Meiosis I Meiosis II Eggs Sperm b + vg + b vg b + vg b vg b vg +

Fig b Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal b + vg + b vg b + vg b vg b + vg + Sperm b vg Parental-type offspring Recombinant offspring Recombination frequency = 391 recombinants 2,300 total offspring  100 = 17% b vg b + vg b vg + Eggs Recombinant chromosomes

Mapping the Distance Between Genes Using Recombination Data: Scientific Inquiry Alfred Sturtevant, one of Morgan’s students, constructed a genetic map, 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 crossover will occur between them and therefore the higher the recombination frequency Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

A linkage map is a genetic map of a chromosome based on recombination frequencies Distances between genes can be expressed as map units; one map unit, or centimorgan, represents a 1% recombination frequency Map units indicate relative distance and order, not precise locations of genes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig RESULTS Recombination frequencies Chromosome 9%9.5% 17% bcnvg

Fig Mutant phenotypes 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

Concept 15.4: Alterations of chromosome number or structure cause some genetic disorders Large-scale chromosomal alterations often lead to spontaneous abortions (miscarriages) or cause a variety of developmental disorders Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Abnormal Chromosome Number In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig Meiosis I (a) Nondisjunction of homologous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II Nondisjunction

Fig Meiosis I Nondisjunction (a) Nondisjunction of homologous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II Meiosis II Nondisjunction

Fig Meiosis I Nondisjunction (a) Nondisjunction of homologous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II Meiosis II Nondisjunction Gametes Number of chromosomes n + 1 n – 1 nn

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 a segment within a chromosome – Translocation moves a segment from one chromosome to another Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Fig Deletion A B C D E F G HA B C E F G H (a) (b) (c) (d) Duplication Inversion Reciprocal translocation A B C D E F G H A B C B C D E F G H A D C B E F G H M N O C D E F G H M N O P Q RA B P Q R

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 Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

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Fig a

Fig b

Fig. 15-UN4 Egg Sperm P generation gametes CBACBA D E F D F E A B C e d f c b a d f e cbacba This F 1 cell has 2n = 6 chromosomes and is heterozygous for all six genes shown ( AaBbCcDdEeFf ). Red = maternal; blue = paternal. + Each chromosome has hundreds or thousands of genes. Four ( A, B, C, F ) are shown on this one. The alleles of unlinked genes are either on separate chromosomes (such as d and e ) or so far apart on the same chromosome ( c and f ) that they assort independently. Genes on the same chromo- some whose alleles are so close together that they do not assort independently (such as a, b, and c ) are said to be linked.