University:
College
Course:
Medical Laboratory Science
Academic year:

2023
Views:

262

Pages:

1
Author:

Carlo M.

HUMAN GENETICS WITH CYTOGENETICS • CHROMOSOME: MUTATION IN NUMBER AND SEQUENCE INTRODUCTION • • • Chromosomes o found in the nucleus o primarily consists of DNA in genes and proteins o duplicated and transmitted via mitosis and meiosis from one generation to another o includes structures that enable them to replicate and remains intact and stable regardless of the number of divisions that happen o differs by size, centromere location and grouped according to size order Chromosome number is the only stable number present in the cell of every organism from birth to death. Its number and structure are stable unless acted upon by outside factor that causes its change, thus affect the phenotypic characteristics of the organism which lead to chromosomal abnormality. LESSON 1: FUNCTION, PARTS AND CLASSIFICATION OF CHROMOSOMES • • • • Chromosomes o Repositories of genes that are constant from the time organism is born o Identified well when the cell is undergoing cell division. o Giemsa staining solution - usually the staining solution used to make their parts visible. Centromere o One of the most important part of chromosome whether it is an autosome or a sex chromosome o It changes location based on the classification of chromosome Telomere o Found at each end of the chromosomes o Helps in the control of cell division. Chromosomes size varies, easy to remember, small, medium and large. This size is one of the bases in grouping them when doing karyotyping. LESSON 2: ABNORMALITY ON THE NUMBER OF CHROMOSOMES • • Chromosomal Abnormality o Result of the change in the number of chromosomes or a change on its structure o These can be observed in karyogram where the chromosomes are arranged according to size. Change in number may either be changed in autosome or sex chromosome number thus can be called as autosomal aneuploid or sexual anueploid. Polyploid - a cell with extra set of chromosomes o Either triploid 3n; tetraploid 4n etc. o Very common in flowering plants not in human. o Normal somatic cell in human contains only two sets of chromosome 2n, total of 46 chromosomes or 23pairs. o Thus 2n+1 means that there is an excess of 1 chromosome like in Down syndrome (trisomy for chromosome 21); Metafemale syndrome, (trisomy for chromosome x), and other kind of trisomies. o Trisomy in whatever number of chromosomes will make the total number 47. It is also possible in human to have 2n+2 or 2n+3. All these will lead to physical, mental and physiological abnormalities, and may also be the cause of abortion. LESSON 3: ABNORMALITY ON THE CHROMOSOME STRUCTURE • • • As mentioned, chromosomal abnormality which usually results to mental and physical deformities is caused not only by the change in the number of chromosomes but also change in the normal structure of the chromosomes. This is much harder to distinguished during karyotyping since the chromosomal number is normal however structure differs from its normal appearance. Change in structure includes: o missing (deletion of chromosome segment) o extra (duplication of segment) o inverted genetic materials within the chromosome (inversion or rotation of segment) o exchange between a non-homologous chromosome (translocation)