Presentation is loading. Please wait.

Presentation is loading. Please wait.

PowerPoint Presentation Materials to accompany

Similar presentations


Presentation on theme: "PowerPoint Presentation Materials to accompany"— Presentation transcript:

1 PowerPoint Presentation Materials to accompany
Genetics: Analysis and Principles Robert J. Brooker CHAPTER 8 VARIATION IN CHROMOSOME STRUCTURE AND NUMBER Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

2 INTRODUCTION Genetic variation refers to differences between members of the same species or those of different species Allelic variations are due to mutations in particular genes Chromosomal aberrations are substantial changes in chromosome structure These typically affect more than one gene They are also called chromosomal mutations 8-2 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

3 INTRODUCTION A change in chromosome number is called a genome mutation
It is the result of changes in the number of Sets of chromosomes OR Numbers of individual chromosomes in a set 8-3 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

4 8.1 VARIATION IN CHROMOSOME STRUCTURE
The study of chromosomal variation is important for several reasons 1. They can have major effects on the phenotype of an organism 2. They can have major effects on the phenotype of the offspring of an organism 3. They have been an important force in the evolution of species 8-4 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

5 Cytogenetics The field of genetics that involves the microscopic examination of chromosomes A cytogeneticist typically examines the chromosomal composition of a particular cell or organism This allows the detection of individuals with abnormal chromosome number or structure This also provides a way to distinguish between species Refer to Figure 8.1a 8-5 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

6 Cytogenetics Cytogeneticists use three main features to identify and classify chromosomes 1. Size 2. Location of the centromere 3. Banding patterns These features are all seen in a Karyotype Figure 8.1c The procedure for making a karyotype was discussed in Chapter 3 (See Figure 3.2) 8-6 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

7 8-7 Figure 8.1 Short arm; For the French, petite Long arm
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

8 Cytogenetics For detailed identification, chromosomes are treated with stains to produce characteristic banding patterns Example: G-banding Chromosomes are exposed to the dye Giemsa Some regions bind the dye heavily Dark bands Some regions do not bind the stain well Light bands In humans 300 G bands are seen in metaphase 2,000 G bands in prophase 8-8 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

9 8-9 Figure 8.1 Banding pattern during metaphase
Banding pattern during prophase Figure 8.1 8-9

10 Cytogenetics The banding pattern is useful in several ways:
1. It distinguishes Individual chromosomes from each other 2. It detects changes in chromosome structure 3. It reveals evolutionary relationships among the chromosomes of closely-related species 8-10 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

11 Mutations Can Alter Chromosome Structure
There are two primary ways in which the structure of chromosomes can be altered 1. The total amount of genetic information in the chromosome can change Deficiencies/Deletions Duplications 2. The genetic material remains the same, but is rearranged Inversions Translocations 8-11 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

12 Deficiency (or deletion) Duplication
The loss of a chromosomal segment Duplication The repetition of a chromosomal segment compared to the normal parent chromosome Inversion A change in the direction of the genetic material along a single chromosome Translocation A segment of one chromosome becomes attached to a different chromosome Simple translocations One way transfer Reciprocal translocations Two way transfer 8-12 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

13 Human chromosome 1 Human chromosome 21 Figure 8.2 8-13

14 Deficiencies A chromosomal deficiency occurs when a chromosome breaks and a fragment is lost Figure 8.3 8-14 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

15 Deficiencies The phenotypic consequences of deficiencies depends on the 1. Size of the deletion 2. Chromosomal material deleted Are the lost genes vital to the organism? When deletions have a phenotypic effect, they are usually detrimental For example, the disease cri-du-chat syndrome in humans Caused by a deletion in the short arm of chromosome 5 Refer to Figure 8.4 8-15 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

16 Chromosomal deletions can be detected by a variety of experimental techniques
Cytological (ie. Microscopic) Used to detect large deletions Molecular Genetic If a mutant population cannot revert back to the wild-type phenotype This is a good indication that the mutation is due to a deletion Deletions can also be revealed by a phenomenon known as pseudodominance One copy of a gene is deleted So the recessive allele on the other chromosome is now expressed 8-16 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

17 Duplications A chromosomal duplication is usually caused by abnormal events during recombination Figure 8.5 8-17 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

18 Duplications Like deletions, the phenotypic consequences of duplications tend to be correlated to size Duplications are more likely to have phenotypic effects if they involve a large piece of the chromosome However, duplications tend to have less harmful effects than deletions of comparable size In humans, relatively few well-defined syndromes are caused by small chromosomal duplications 8-18 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display


Download ppt "PowerPoint Presentation Materials to accompany"

Similar presentations


Ads by Google