Chromosomal Aberrations - Veterinary Medicine PDF

# Chromosomal aberrations ## Faculty of Veterinary Medicine Department of Animal Wealth Development - Genetics and Genetic Engineering- 1th Level Students ### Chromosomal aberrations or abnormalities. - Changes in the structure or number of chromosomes, which are strands of condensed genetic ma...

# Chromosomal aberrations ## Faculty of Veterinary Medicine Department of Animal Wealth Development - Genetics and Genetic Engineering- 1th Level Students ### Chromosomal aberrations or abnormalities. - Changes in the structure or number of chromosomes, which are strands of condensed genetic material. - They usually occur as a result of errors in cell division. - They can be inherited from a parent or be de novo. ### There are two types of chromosomal aberrations: 1. **Numerical chromosomal aberrations:** any changes in chromosome numbers, either decrease or increase of one or more chromosomes or even one or more haploid sets. 2. **Structural chromosomal aberrations:** changes in normal structure of chromosomes or the arrangement of genetic material within or between individual chromosomes. ### Numerical chromosomal aberrations - People have 23 chromosome pairs (46 chromosomes) in each cell - one inherited from the mother and one from the father. - The normal somatic cell contains two sets of chromosomes (2n) (diploid). Normal gamete cell contains one set of chromosomes (1n) (haploid). ### Causes of numerical chromosomal aberrations: Usually caused by failure of chromosome division (non-disjunction), which results in cells with an extra chromosome or deficient chromosome. **Diagram:** The diagram shows the difference between proper disjunction and nondisjunction. Proper disjunction occurs in anaphase during cell division, while nondisjunction can result in the formation of one daughter cell with an extra chromosome and one daughter cell with a deficient chromosome. ### Numerical chromosomal aberrations (ploidy) include: 1. **Aneuploidy:** differ from the standard chromosome number in a single chromosome (2n±1, 2n±2) include: - Hypopolypliody (Monosomy, Nullisomy) - Hyperpolypliody (Trisomy, Tetrasomy) 2. **Eupliody:** differ from the standard chromosome number, in multiples of n (1n, 3n, 4n) include: - Monopliody - Dipliody - Polypliody **Diagram:** The diagram shows the different types of ploidy. Euploidy refers to a change in the number of complete chromosome sets, while aneuploidy refers to a change in the number of individual chromosomes. Aneuploidy can be further classified into hypoploidy, which involves the loss of chromosomes, and hyperploidy, which involves the gain of chromosomes. ### Anupliody **1-Trisomy** A trisomy is a chromosomal condition characterized by an additional chromosome (one extra chromosome of a homologous pair 2n+1). This means they have 47 chromosomes instead of 46. All trisomies could be due to nondisjunction. #### Examples of trisomy **1. Klinefelter syndrome (KS):** - Male has an additional copy of the X chromosome. - The primary features are infertility due to no production of sperms, show some feminized characters and small, poorly functioning testicles. - It is common in cats. A sterile male cat which has unusual color (tortoise-shell). That color is normal in heterozygous females as it is controlled by a codominant X linked gene, where O gives orange color while O gives black color. Karyotype (39, XXY). **Diagram:** The diagram shows the different combinations of chromosomes (O for orange color, o for black color, X for female and Y for male) that result in different color coat patterns in male and female cats. The last one is called "tortoise shell male (Ks)". **2. Triple X condition:** It is observed in unfertile mares; it may be sterile but sometimes normal and able to produce normal offspring, when cytologically. ( Karyotype: (65, XXX) Trisomy in X chromosome. **Diagram:** The diagram shows a karyotype of a female with triple X syndrome. Each pair of chromosomes is arranged into pairs from 1 to 22. Below the chromosomes are the three X chromosomes, showing that the female has Trisomy in X chromosome, known as triple X syndrome. **3. XYY male condition:** Observed in male humans where the individual is taller than 180 cm, mentally retarded, affected with acne, and usually tends to be criminal. (Karyotype: (47, XYY) **Diagram:** The diagram shows a karyotype of a male with XYY syndrome; the chromosomes are arranged from 1 to 22, followed by X and Y chromosomes. **4. Down syndrome (mongolism): Karyotype: (47, 21+)** Trisomy in autosomal chromosome number 21. The most common autosomal trisomy with one in 700 live births affected. The main symptom is Mongol-like eye shape. Affected persons are short and have a small head, idiotic features, broad hands, and are mentally retarded. **Image:** This is an image of a child with Down syndrome, which is a condition resulting from a trisomy of chromosome 21. The child has characteristic features including almond-shaped eyes and a flattened face. **Diagram:** The diagram shows a karyotype of an individual with Down syndrome, where the autosomal chromosome number 21 is a trisomy. **5. Patau syndrome:** (Karyotype: (47, 13+). Trisomy in autosomal chromosome number 13.) It is a rare condition, occurring in one out of every 20,000 live births. Affected children have several malformations such as harelip, cleft palate, and polydactyl, and are mentally retarded. They live less than six months. **Image:** This is an image of a child with Patau syndrome, a trisomy of chromosome 13. It is characterized by deformities of the face, brain, and heart, such as a cleft palate and the absence of a nose bridge. **Diagram:** The diagram shows the karyotype of an individual with Patau syndrome, which shows Trisomy in chromosome 13. **6. Edwards syndrome:** (Karyotype (47,18+).) Trisomy in chromosome number 18. Occurs in around one in 6,000 live births. Around 80% of affected individuals are females. The incidence increases as the mother's age increases. The majority of fetuses with the syndrome die before birth. The syndrome has a very low rate of survival due to heart abnormalities, kidney malformations, and other internal organ disorders. **Image:** This is an image of a child with Edwards syndrome, characterized by the trisomy of chromosome 18. Common features include a small jaw and a clenched fist, similar to those seen in Down syndrome. **Diagram:** The diagram shows the karyotype of an individual with Edwards syndrome where chromosome number 18 is a trisomy. **7. Trisomy in cattle:** - Trisomy in chromosome 23 causes dwarf calves. - Trisomy in chromosome 17 causes Bachygnathia (very short lower jaw). **Image:** The image shows two calves: the one on the left is a normal calf, while the one on the right is a dwarf calf. **Image:** The image shows a calf with Bachygnathia, characterized by a very short lower jaw. **2. Tetrasomy:** four copies instead of normal two of a particular chromosome (2n+2). **3. Monosomy:** The term "monosomy" is used to describe the absence of one member of a pair of chromosomes (diploid lacking 1 chromosome 2n. Therefore, there are 45 chromosomes in each cell of the body instead of the usual 46. In most cases, embryos with monosomy of the autosomes or sex chromosomes are not viable. Some individuals with monosomy of the sex chromosomes (45XO genotype) can survive. #### Example of monosomy: **1. Turner syndrome (63, XO):** A condition that affects females and involves the partial or complete absence of an X chromosome. This case is discovered in infertile mares. **Appearance:** generally normal but the estrous cycle is irregular or even absent. Uterus and ovaries are smaller than normal. Ovaries lack follicles. This case is also reported in mice, rats, pigs, horses, and humans. **Diagram:** The diagram shows the karyotype of a female with Turner syndrome, a condition caused by a monosomy of the X chromosome. The chromosome set is arranged from 1 to 22, followed by X and Y chromosomes. The female in the diagram has only one X chromosome. **2. Nullisomy:** diploid lacking one chromosome pair 2n-2. ### Mechanism of aneuploidy 1. **Mietic non disjunction failure of a homologous pair to separate during meiosis.** 2. **Occurance of translocation.** ### Eupliody **1. A monoploid** has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally haploid. Males of bees and other Hymenoptera, for example, are monoploid. **2. Polyploidy:** a heritable condition in which the cells of an organism have more than two paired (homologous) sets of chromosomes. Most species are diploid, meaning they have two sets of chromosomes. One set is inherited from each parent. However, some organisms are polyploid, and polyploidy is especially common in plants. Polyploidy may occur due to: - **Polyandry fertilization** of one ovum by more than one sperm. - **Polygyny:** Failure of exclude the one or more polar body and fertilized by one sperm. **Diagram:** The diagram shows the processes of polyandry and polygyny which lead to polyploidy. ### Mechanism of euploidy - **Somatic doubling.** - **Failure of cytoplasmic division.** ### N.B: 1. Most aneuploidies are incompatible with life resulting in spontaneous abortions except for trisomy 21, 13, and 18 and eupliody, monosomy X, which can result in viable pregnancies. **Image:** The image shows a text stating "Thank You" with a golden design behind it.