20 genetics
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This document discusses different types of genetic disorders including Mendelian disorders caused by single gene mutations inherited in autosomal dominant, recessive, or X-linked patterns. It also discusses cytogenetic disorders caused by chromosomal abnormalities like aneuploidy resulting in extra or missing chromosomes as in Down syndrome. Finally, it mentions multifactorial disorders caused by both genetic and environmental factors, giving diabetes and hypertension as examples.
20 genetics
- 1. Genetic disorders By Shatha al sulh
- 3. Types of mutations • It is permanent damage of the DNA. • It may lead to inherited diseases (if the mutation affect germ cells), congenital malformation or cancer (if affecting somatic cells). • Classified into: – Genome mutations: loss or gain of a whole chromosome (affecting the number of chromosomes) lead to monosomy or trisomy. – Chromosome mutations: structural changes within a chromosome due to rearrangement of genetic materials. – Gene mutations: affecting individual genes within a chromosome.
- 4. Classification of genetic disorders • Mendelian disorders. • Cytogenetic (chromosomal) disorders. • Disorders of multifactorial inheretence.
- 5. I-Mendelian disorders • Caused by mutations affecting single genes. • Normally: each gene is represented as a pair (alleles) on a specific gene locus on the corresponding chromosomes. • Inherited as: – Autosomal dominant disorders – Autosomal recessive disorders – X-linked disorders: resulting from a mutant gene in the X chromosome • X-linked recessive disorders • X-linked domenant disorders
- 6. Cytogenetic disorders (cont.) • Numerical (number) abnormalities: – Euploidy: exact multiple of normal haploid (n) (23), may be 2n (normal diploidy, 46) or abnormal (3n triploidy 69 or 4n tetraploidy, that may affect all cells & is incompetable with life or affect some cells as cancer cells). – Aneuploidy: abnormal chromosome number which is not an exact multiple of haploid, results from non-disjunction of 1 chromosome during gametogenesis, so 1 gamete with extra & another with a missing chromosome, so the zygote will be either 2n+1 (trisomy 47) or 2n -1 (monosomy 45) e.g trisomy 21 (down syndrome) which is the most common chromosomal disorder. – Mosaicism: due to mitotic errors in early development resulting in 2 or > population of cells in the same individual e.g 45xx/46xx/47xxx.
- 7. III-Multifactorial disorders • Diseases resulting from genetic + environmental disorders. • E.g: –Diabetes mellitus: genetic error + other factors as viral infection of pancreas, obesity or stress. –Hypertension: genetic factor + other factors as stress, obesity or excess salt in diet.