YIJC [H2] CI2.7_Chromosomal Aberration (N)(S) vetted (wo checkpoint answers)

2024 JC1 BIOLOGY LECTURE NOTES CORE IDEA 2: GENETICS AND INHERITANCE TOPIC 2.7: CHROMOSOMAL ABERRATION Learning Outcomes (modified): (l) Explain what is meant by the terms chromosomal aberration. For chromosomal aberration, knowledge of numerical aberration (including aneuploidy, as in the case of trisomy 21, i.e. Down syndrome) and structural aberration (including translocation, duplication, inversion and deletion) is required. Use the knowledge gained in this section in new situations or to solve related problems. References: Reece, J. B. et al. (2018). Campbell Biology (11th Ed). Chapter 17: From Gene to Protein, pp407 – 410. Reece, J. B. et al. (2018). Campbell Biology (11th Ed). Chapter 15: Linkage and Chromosomes, pp356 – 359. Note: This textbook is available in our library. You may wish to borrow it to supplement your reading when necessary. H2

2 1. Introduction Chromosomal aberrations refer to changes or abnormalities in the structure or number of chromosomes within a cell. 2. Overview of Chromosomal Aberration There are two main types of chromosomal aberrations: 1. Numerical aberrations:  Aneuploidy: This occurs when a cell has an abnormal number of chromosomes, either too many or too few. It can result from errors during cell division (mitosis or meiosis). o Trisomy: Having an extra copy of a particular chromosome, resulting in three copies instead of two (e.g., Down syndrome, which is caused by trisomy of chromosome 21). o Monosomy: Missing a copy of a particular chromosome, resulting in only one copy instead of two (e.g., Turner syndrome, caused by monosomy of the X chromosome). 2. Structural aberrations:  Deletions: A portion of a chromosome is missing or deleted.  Duplications: A part of a chromosome is duplicated or repeated.  Inversions: A segment of a chromosome is reversed in orientation.  Translocations: A segment of one chromosome is attached to a different chromosome. Fig 2.1: Overview of Chromosomal Aberration Mutation Chromosomal aberrations Gene Mutations Change in chromosome structure Change in chromosome numbers Polyploidy Aneuploidy Autopolyploids Allopolyploids deletion duplication inversion translocation

3 These chromosomal aberrations can occur spontaneously or be induced by environmental factors like radiation or certain chemicals. They can lead to genetic disorders, developmental abnormalities, or even cell death, depending on the specific aberration and the genes involved. 3. Chromosome Aberration 3.1 Structural Aberration There are different types of structural chromosomal aberrations. Chromosome structural aberrations can arise through physical breakage and rejoining of the DNA that constitutes the chromosome. Fig. 3.1.1: Structural aberration Learning Outcome 2(l) modified: