Presentation is loading. Please wait.

Presentation is loading. Please wait.

The Chromosomal Basis of Inheritance

Similar presentations


Presentation on theme: "The Chromosomal Basis of Inheritance"— Presentation transcript:

1 The Chromosomal Basis of Inheritance
Chapter 15 The Chromosomal Basis of Inheritance

2 Explain the chromosomal theory of inheritance and its discovery
You should be able to: Explain the chromosomal theory of inheritance and its discovery Explain why sex-linked diseases are more common in human males than females Distinguish between sex-linked genes and linked genes Explain how meiosis accounts for recombinant phenotypes Explain how linkage maps are constructed Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

3 Explain how nondisjunction can lead to aneuploidy
Define trisomy, triploidy, and polyploidy Distinguish among deletions, duplications, inversions, and translocations Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

4 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

5 Fig. 15-1 Figure 15.1 Where are Mendel’s hereditary factors located in the cell?

6 Mitosis and meiosis were first described in the late 1800s
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

7 yellow-round seeds (YyRr)
Fig. 15-2a Yellow-round seeds (YYRR) Green-wrinkled seeds ( yyrr) P Generation y Y r R R r Y y Meiosis Fertilization y r R Y Figure 15.2 The chromosomal basis of Mendel’s laws Gametes All F1 plants produce yellow-round seeds (YyRr)

8 0.5 mm All F1 plants produce yellow-round seeds (YyRr) F1 Generation
Fig. 15-2b All F1 plants produce yellow-round seeds (YyRr) 0.5 mm F1 Generation R R y y r r Y Y LAW OF SEGREGATION The two alleles for each gene separate during gamete formation. Meiosis LAW OF INDEPENDENT ASSORTMENT Alleles of genes on nonhomologous chromosomes assort independently during gamete formation. R r r R Metaphase I Y y Y y 1 1 R r r R Anaphase I Y y Y y R r Metaphase II Figure 15.2 The chromosomal basis of Mendel’s laws r R 2 2 Y y Y y y Y Y Y Y y y y Gametes R R r r r r R R 1 4 YR 1 4 yr 1 4 Yr 1 4 yR 3 3

9 An F1  F1 cross-fertilization
Fig. 15-2c F2 Generation An F1  F1 cross-fertilization 3 3 9 : 3 : 3 : 1 Figure 15.2 The chromosomal basis of Mendel’s laws

10 Morgan’s Experimental Evidence: Scientific Inquiry
The first solid evidence associating a specific gene with a specific chromosome came from Thomas Hunt Morgan, an embryologist Morgan’s experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel’s heritable factors Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

11 Morgan’s Choice of Experimental Organism
Several characteristics make fruit flies a convenient organism for genetic studies: They breed at a high rate A generation can be bred every two weeks They have only four pairs of chromosomes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

12 Traits alternative to the wild type are called mutant phenotypes
Morgan noted wild type, or normal, phenotypes that were common in the fly populations Traits alternative to the wild type are called mutant phenotypes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

13 Fig. 15-3 Figure 15.3 Morgan’s first mutant

14 Morgan’s finding supported the chromosome theory of inheritance
Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type) The F1 generation all had red eyes The F2 generation showed the 3:1 red:white eye ratio, but only males had white eyes Morgan determined that the white-eyed mutant allele must be located on the X chromosome Morgan’s finding supported the chromosome theory of inheritance Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

15 EXPERIMENT P  Generation F1 All offspring Generation had red eyes
Fig. 15-4a EXPERIMENT P Generation F1 All offspring had red eyes Generation Figure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?

16 RESULTS F2 Generation Fig. 15-4b
Figure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have?

17 CONCLUSION + P X X Generation  X Y + Sperm Eggs + + F1 + Generation +
Fig. 15-4c CONCLUSION + P w w X X Generation X Y + w w Sperm Eggs + + F1 w w + Generation w w + w Figure 15.4 In a cross between a wild-type female fruit fly and a mutant white-eyed male, what color eyes will the F1 and F2 offspring have? Sperm Eggs + + w w + F2 w Generation w w w + w

18 Concept 15.2: Sex-linked genes exhibit unique patterns of inheritance
In humans and some other animals, there is a chromosomal basis of sex determination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

19 The Chromosomal Basis of Sex
In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosome Only the ends of the Y chromosome have regions that are homologous with the X chromosome The SRY gene on the Y chromosome codes for the development of testes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

20 Fig. 15-5 X Y Figure 15.5 Human sex chromosomes

21 Females are XX, and males are XY
Each ovum contains an X chromosome, while a sperm may contain either an X or a Y chromosome Other animals have different methods of sex determination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22 (a) The X-Y system 44 + XY 44 + XX Parents 22 + X 22 + X 22 + Y or +
Fig. 15-6a 44 + XY 44 + XX Parents 22 + X 22 + X 22 + Y or + Sperm Egg Figure 15.6 Some chromosomal systems of sex determination 44 + XX 44 + XY or Zygotes (offspring) (a) The X-Y system

23 Inheritance of Sex-Linked Genes
The sex chromosomes have genes for many characters unrelated to sex A gene located on either sex chromosome is called a sex-linked gene In humans, sex-linked usually refers to a gene on the larger X chromosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

24 Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressed A female needs two copies of the allele A male needs only one copy of the allele Sex-linked recessive disorders are much more common in males than in females Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

25 (a) (b) (c) Sperm Sperm Sperm Eggs Eggs Eggs XNXN  XnY XNXn  XNY
Fig. 15-7 XNXN XnY XNXn XNY XNXn XnY Sperm Xn Y Sperm XN Y Sperm Xn Y Eggs XN XNXn XNY Eggs XN XNXN XNY Eggs XN XNXn XNY XN XNXn XNY Xn XnXN XnY Xn XnXn XnY Figure 15.7 The transmission of sex-linked recessive traits (a) (b) (c)

26 Some disorders caused by recessive alleles on the X chromosome in humans:
Color blindness Duchenne muscular dystrophy Hemophilia Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

27 X Inactivation in Female Mammals
In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development The inactive X condenses into a Barr body If a female is heterozygous for a particular gene located on the X chromosome, she will be a mosaic for that character Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

28 X chromosomes Allele for orange fur Early embryo: Allele for black fur
Fig. 15-8 X chromosomes Allele for orange fur Early embryo: Allele for black fur Cell division and X chromosome inactivation Two cell populations in adult cat: Active X Inactive X Active X Black fur Orange fur Figure 15.8 X inactivation and the tortoiseshell cat

29 Each chromosome has hundreds or thousands of genes
Concept 15.3: Linked genes tend to be inherited together because they are located near each other on the same chromosome Each chromosome has hundreds or thousands of genes Genes located on the same chromosome that tend to be inherited together are called linked genes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

30 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 body color and wing size Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

31 b+ vg+ b vg  Parents in testcross b vg b vg b+ vg+ b vg Most or
Fig. 15-UN1 b+ vg+ b vg Parents in testcross b vg b vg b+ vg+ b vg Most offspring or b vg b vg

32 EXPERIMENT Fig. 15-9-1 P Generation (homozygous) b+ b+ vg+ vg+
Wild type (gray body, normal wings) Double mutant (black body, vestigial wings) b+ b+ vg+ vg+ b b vg vg Figure 15.9 How does linkage between two genes affect inheritance of characters?

33 EXPERIMENT Fig. 15-9-2 P Generation (homozygous) b+ b+ vg+ vg+
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 Figure 15.9 How does linkage between two genes affect inheritance of characters?

34 EXPERIMENT Fig. 15-9-3 P Generation (homozygous) b+ b+ vg+ vg+
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 b vg+ Wild type (gray-normal) Black- vestigial Gray- vestigial Black- normal b vg Figure 15.9 How does linkage between two genes affect inheritance of characters? Sperm b+ b vg+ vg b b vg vg b+ b vg vg b b vg+ vg

35 EXPERIMENT RESULTS Fig. 15-9-4 P Generation (homozygous) b+ b+ vg+ vg+
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 b vg+ Wild type (gray-normal) Black- vestigial Gray- vestigial Black- normal b vg Figure 15.9 How does linkage between two genes affect inheritance of characters? 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 : : RESULTS 965 : 944 : 206 : 185

36 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

37 However, nonparental phenotypes were also produced
Understanding this result involves exploring genetic recombination, the production of offspring with combinations of traits differing from either parent Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

38 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

39 Recombination of Unlinked Genes: Independent Assortment of Chromosomes
Mendel observed that combinations of traits in some offspring differ from either parent Offspring with a phenotype matching one of the parental phenotypes are called parental types Offspring with nonparental phenotypes (new combinations of traits) are called recombinant types, or recombinants A 50% frequency of recombination is observed for any two genes on different chromosomes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

40 YR yr Yr yR yr YyRr yyrr Yyrr yyRr Gametes from yellow-round
Fig. 15-UN2 Gametes from yellow-round heterozygous parent (YyRr) YR yr Yr yR Gametes from green- wrinkled homozygous recessive parent ( yyrr) yr YyRr yyrr Yyrr yyRr Parental- type offspring Recombinant offspring

41 Recombination of Linked Genes: Crossing Over
Morgan discovered that genes can be linked, but the linkage was incomplete, as evident from recombinant phenotypes Morgan proposed that some process must sometimes break the physical connection between genes on the same chromosome That mechanism was the crossing over of homologous chromosomes Animation: Crossing Over Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

42 Black body, vestigial wings
Fig Testcross parents Gray body, normal wings (F1 dihybrid) Black body, vestigial wings (double mutant) b+ vg+ b vg b vg b vg Replication of chromo- somes Replication of chromo- somes b+ vg+ b vg b+ vg+ b vg b vg b vg b vg b vg Meiosis I b+ vg+ Meiosis I and II b+ vg b vg+ b vg Meiosis II Recombinant chromosomes Figure Chromosomal basis for recombination of linked genes 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+ b vg b vg b vg b vg Sperm Parental-type offspring Recombinant offspring Recombination frequency 391 recombinants =  100 = 17% 2,300 total offspring

43 Black body, vestigial wings
Fig a Testcross parents Gray body, normal wings (F1 dihybrid) Black body, vestigial wings (double mutant) b+ vg+ b vg b vg b vg Replication of chromo- somes Replication of chromo- somes b+ vg+ b vg b+ vg+ b vg b vg b vg b vg b vg Meiosis I b+ vg+ Meiosis I and II b+ vg b vg+ Figure Chromosomal basis for recombination of linked genes b vg Meiosis II Recombinant chromosomes b+ vg+ b vg b+ vg b vg+ b vg Eggs Sperm

44 965 944 Black- vestigial 206 Gray- vestigial 185 Black- normal
Fig b Recombinant chromosomes 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+ Figure Chromosomal basis for recombination of linked genes b vg b vg b vg b vg Sperm Parental-type offspring Recombinant offspring Recombination frequency 391 recombinants =  100 = 17% 2,300 total offspring

45 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

46 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

47 RESULTS Recombination frequencies 9% 9.5% Chromosome 17% b cn vg
Fig RESULTS Recombination frequencies 9% 9.5% Chromosome 17% Figure Constructing a linkage map b cn vg

48 Genes that are far apart on the same chromosome can have a recombination frequency near 50%
Such genes are physically linked, but genetically unlinked, and behave as if found on different chromosomes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

49 Sturtevant used recombination frequencies to make linkage maps of fruit fly genes
Using methods like chromosomal banding, geneticists can develop cytogenetic maps of chromosomes Cytogenetic maps indicate the positions of genes with respect to chromosomal features Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

50 Mutant phenotypes Short aristae Black body Cinnabar eyes Vestigial
Fig Mutant phenotypes Short aristae Black body Cinnabar eyes Vestigial wings Brown eyes 48.5 57.5 67.0 104.5 Figure A partial genetic (linkage) map of a Drosophila chromosome Long aristae (appendages on head) Gray body Red eyes Normal wings Red eyes Wild-type phenotypes

51 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

52 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

53 Meiosis I (a) Nondisjunction of homologous
Fig Meiosis I Nondisjunction Figure Meiotic nondisjunction For the Cell Biology Video Nondisjunction in Mitosis, go to Animation and Video Files. (a) Nondisjunction of homologous chromosomes in meiosis I (b) Nondisjunction of sister chromatids in meiosis II

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

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

56 Aneuploidy results from the fertilization of gametes in which nondisjunction occurred
Offspring with this condition have an abnormal number of a particular chromosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

57 A monosomic zygote has only one copy of a particular chromosome
A trisomic zygote has three copies of a particular chromosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

58 Polyploidy is common in plants, but not animals
Polyploidy is a condition in which an organism has more than two complete sets of chromosomes Triploidy (3n) is three sets of chromosomes Tetraploidy (4n) is four sets of chromosomes Polyploidy is common in plants, but not animals Polyploids are more normal in appearance than aneuploids Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

59 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

60 Reciprocal translocation
Fig A B C D E F G H A B C E F G H Deletion (a) A B C D E F G H A B C B C D E F G H Duplication (b) A B C D E F G H A D C B E F G H (c) Inversion Figure Alterations of chromosome structure A B C D E F G H M N O C D E F G H (d) Reciprocal translocation M N O P Q R A B P Q R

61 Human Disorders Due to Chromosomal Alterations
Alterations of chromosome number and structure are associated with some serious disorders Some types of aneuploidy 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 syndrome, characteristic of the type of aneuploidy Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

62 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

63 Fig Figure Down syndrome

64 Fig a Figure Down syndrome

65 Fig b Figure Down syndrome

66 The alleles of unlinked genes are either on separate chromosomes
Fig. 15-UN4 Sperm Egg C B A c b a P generation gametes D E d e + F f 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. This F1 cell has 2n = 6 chromosomes and is heterozygous for all six genes shown (AaBbCcDdEeFf ). Red = maternal; blue = paternal. D e C B d Each chromosome has hundreds or thousands of genes. Four (A, B, C, F) are shown on this one. A 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. E F f a c b

67 Fig. 15-UN6

68 Fig. 15-UN7

69 Fig. 15-UN8

70 Fig. 15-UN9

71 You should now be able to:
Explain the chromosomal theory of inheritance and its discovery Explain why sex-linked diseases are more common in human males than females Distinguish between sex-linked genes and linked genes Explain how meiosis accounts for recombinant phenotypes Explain how linkage maps are constructed Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

72 Explain how nondisjunction can lead to aneuploidy
Define trisomy, triploidy, and polyploidy Distinguish among deletions, duplications, inversions, and translocations Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings


Download ppt "The Chromosomal Basis of Inheritance"

Similar presentations


Ads by Google