PCB3063_Chapter08_Spring2018 (1).doc - PCB 3063 Chapter 8 CHAPTER 8 VARIATION IN CHROMOSOME STRUCTURE AND NUMBER INTRODUCTION CHROMOSOME STUDIES •

PCB3063_Chapter08_Spring2018 (1).doc - PCB 3063 Chapter 8...

This preview shows page 1 - 4 out of 16 pages.

PCB 3063 Chapter 8 CHAPTER 8 VARIATION IN CHROMOSOME STRUCTURE AND NUMBER INTRODUCTION CHROMOSOME STUDIES CYTOGENETICS is the field that involves the microscopic examination of chromosomes - It typically examines the chromosomal composition of a specific 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 8.1 Types of chromosomes • Chromosomes can be divided into four main types based on their centromere location • Three main features are used to identify and classify chromosomes 1. Size 2. Location of the centromere 3. Banding patterns - These features are all seen in a KARYOTYPE CHROMOSOMAL VARIATION • Chromosomal variation can occur in two basic ways: Structure and Number • 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 organism’s OFFSPRING 3. They have been an important force in the EVOLUTION of species • A given abnormality may be present in all body cells, or in some of them - MOSAICISM = The presence of two or more cell lines in an individual, one or more of which are abnormal VARIATION IN CHROMOSOME NUMBER
Image of page 1
PCB 3063 Chapter 8 • Chromosome numbers can vary in two ways (Figure 8.15) - EUPLOIDY - Changes in the entire set of chromosomes - Occurs occasionally in animals and frequently in plants - ANUEPLOIDY - Changes in individual chromosomes rather than in the complete set - Regarded as abnorma l conditions • In general changes in chromosome number have a MORE SEVERE effect on survival than changes in chromosome structure ANEUPLOIDY • Aneuploidy includes - Monosomy = One homologue is missing - Trisomy = One extra homologue is present - Tetrasomy = Two extra homologues are present - Double monosomy = Two different homologues are missing - Double trisomy = Two different extra homologues are present - Nullisomy = A whole pair of chromosomes is missing • Note: These definitions apply to a DIPLOID cell • Aneuploidy commonly causes an abnormal phenotype - It leads to an IMBALANCE in the amount of gene products - Refer to Figure 8.16 Monosomy - Tolerated in some plants - In Drosophila - Haplo-IV = Survive but have problems! Missing one small copy of chromosome 4 have limited flight - Lethal in humans except for the X chromosome we can only tolerate 1 copy of chromosome X Turner Syndrome
Image of page 2
PCB 3063 Chapter 8 - Syndrome first described by Henry Turner in 1938 - Chromosomal abnormality first described by Ford et al. in 1959 - Karyotype = 45, X 45, XO - Frequency = 1 in 10,000 LIVE FEMALE BIRTHS - Features = - Short stature - Webbed neck - Underdeveloped ovaries (streak gonads) STERILE - Wide chest with widely-spaced nipples - About normal intelligence - Failure to develop secondary sexual characteristics - 40-50% of patients are mosaics - ~99% of Turner syndrome conceptions are lost prenatally - Therapy may help - Anabolic steroids - Estrogen
Image of page 3
Image of page 4

You've reached the end of your free preview.

Want to read all 16 pages?

  • Fall '08
  • JEFFERYS

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask You can ask ( soon) You can ask (will expire )
Answers in as fast as 15 minutes