University:
Kentucky State University
Course:
BIO 307 | Genetics
Academic year:

2019
Views:

205

Pages:

22
Author:

Quintin Ware

Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure • Duplication : is the opposite of deletion; it is the gain of DNA region leading to multiple copies of chromosomal parts and their located genes. • Known human disorders include Charcot-Marie-Tooth disease type 1A, which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17. • e.g., DiGeorge syndrome, Smith Magenis syndrome 1 Sheet 1 • The basic rule says that the duplication mutation is less effect on humans than the deletion • Alougtho, this not main is no effect on human • Example on duplication syndrome in the last line in slide 2 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Duplication of the same direction as the original (a direct duplication) or in opposition (an inverted duplication). • The phenotypes associated with duplications are typically less severe than those associated with comparable deletions. direct duplication 3 4 Sheet # 2 To understand the direction of duplication ..look at the picture, there are two regions, pink and green. If the duplication was in same direction as the original, that main the region was pink–green and after duplication become pink-green,pink-green …this type is called the (direct duplication ) If happen a change in agreement during duplication in which became after copies >>pink-green,green-pink …it will be called the (inverted duplication ) Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure • An inversion is chromosomal rearrangement in which a segment of chromosomal DNA has reversed position inside the same chromosomal molecule. • The most common inversion seen in humans is on chromosome 9. • An inversion does not involve a loss of genetic information, but simply rearranges the linear gene sequence during DNA recombination of chromosomal cross over. 5 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure • One part of chromosome has been ﬂipped around in opposite direction • individual may be normal unless inversion breakpoints are in middle of a gene or unless inversion affects centromeres. • However, in individuals with an inversion there is an increased production of abnormal chromatids. This leads to lowered fertility due to production of unbalanced gametes. 6 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Inversions are intrachromosomal rearrangements created when a chromosome breaks in two places and the material between the two breakpoints reverses orientation. • Inversions can be pericentric or paracentric 7 Sheet# 3 • dependantke some types of invention , it is depandant on where the inversion happens in which: • If the inversion happens on tow arm of chromosome ,it will be called the (pericenter inversion) ..look in the picture mate • If the inversion happened on one arm of a chromosome either long or short ..it will be called the (paracentric inversion ) which is including the centromere 8 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Translocations : A chromosomal abnormality caused by an exchange of parts between non-homologous chromosomes. • Bases break off from one chromosome and re-attach to a completely different chromosome (a non-homozygous pair). • often lead to duplications of one chromosomal part and deletions of another part. • Some separated genes of different chromosomes are fused together after translocation, which is common phenomenon in cancer diseases. • Translocations can be classiﬁed into two major types: 1. Reciprocal 2. Robertsonian Sheet # 4 • she said that translocation between homologous chromosomes is normal and important in making new characters on the new generations (cross-linking )>>the exchange between the same chromosome e.g. chro 3 trans with a material copy with parental copy, but the not normal between the non-homologs like chro 3 with chro 9 ..it is not abnormal, • • and it is the most resonate to set cancer in the world like the translocation that happened between the chro ( 9-22). 10 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure • Reciprocal translocations occur when genetic material is exchanged between nonhomologous chromosomes (other than acrocentric chromosomes). Because these translocations involve only a single cell and the genetic material is balanced, there is often no consequence. Rarely, however, a reciprocal translocation may alter the expression or structure of an oncogene or a tumor suppressor gene, conferring an abnormal growth advantage to the cell. • Robertsonian translocations occur chromosomes (13, 14, 15, 21, and 22). only in the acrocentric 11 Sheet # 5 • discussed we will not focus on details, but we should now that • Reciprocal translocations : It happens in all types of chromosomes that we have disscued in previous lectures (she returns on slide 21 of chap ), except the Acrocentric Robertsonian translocations: It will happen in the Acrocenteric type, and in normal humans, the (13,14,15,21,22) these chromosomes consider the acrocentric 12 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Reciprocal translocations 13 Sheet # 6 She seaid you should know how we do represent on translocation : • t (2p;8p) • t= translocation happed • The number represents the number of chro • P = it’s means the short arm • q= it’s maine the long arm • The arrangement important the 2p go to 8p, and the opposite not true • She said I could ask you, the translocation happens between the long arm from chro 9 with shorter arm from chro 22 ..the form of this translocation represents: • A (9p;22q) B (9q;22p) C (22p;9q) D (22q;9p) 14 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Robertsonian translocations • Two q arms of two different chromosomes come together • Two p arms are lost entirely • An entire chromosome has attached to another at the centromere • in humans these only occur with chromosomes 13, 14, 15, 21, and 22. 15 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Robertsonian translocations 16 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Isochromosomes • An isochromosome consists of two copies of the same chromosome arm joined through a single centromere in such a way that the arms form mirror images of one another. 17 Lecture # 7: Mutations B. Chromosomal mutations :2. Abnormal Structure Ring chromosome: • is an aberrant chromosome whose ends have fused together to form a ring • patients have severe growth retardation. 18 Sheet # 7 • In the isochromosome >>>>the homologs chromosome content two copies >>>>>the sarcomere usually separate the p arm on q arm, but in this case, the tow sarcomere will separate the tow p arms on tow q arms • In ring chro>>>the limps of chro contain telomere (it’s function save the integrity of chro )…if there is a mutation on it >>the chromo will try to protect itself by turning on the form cycles ..this is a huge abnormality, in this form it can’t divide, can we consider we lost it Principles of Genetics and molecular biology Dr. Ola AL-FAWARES 19 Causes of mutations Lecture # 7: Mutations • Mutations can occur spontaneously (naturally) as an errors in DNA replication, repair or recombination that result in basepair substitutions, insertions or deletions. • Alternatively mutations may be induced (artiﬁcially) as a result of exposure to mutagens. • Mutagen = Physical or chemical agents that interact with DNA to cause mutations. • Radiation is the most common physical mutagen in nature and has been used in the laboratory to induce mutations. • Several groups of chemical mutagens are known including base analogues, which are chemicals that are structurally similar to normal DNA bases, but make incorrect base pairing. 20 Summary Lecture # 7: Mutations P 21 22

Chromosomal Mutations Abnormal Structure

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