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Basic concepts in genetics
- 1. BY Dr. Ayesha SultanaA R. PG, Practice of Medicine(Part-I) *Basic Concepts in Genetics
- 4. *WHAT IS GENETICS? *Geneticsrefers to the study of genes, heredity & genetic variation in the living organism.
- 5. In the mid-1800s,the rules underlying patterns of inheritance were uncovered in a series of experiments performed by an Austrian monk named Gregor Mendel. *Gregor Mendel is called as “Father of Genetics”.
- 7. *chromosome *Greek chroma-colour; soma- body *Chromosome is collection of genes made of protein & one molecule of DNA. *Each chromosome has a short arm called ‘p’(petit) & a long arm called ‘q’. *These arms are divided into region, bands & sub-bands, numerically, e.g., 7q21.2 means long arm of chromosome 7, region 2, band 1 & sub-band 2.
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- 9. *chromosome *Types- *Metacentric chromosome- centromere locatedin the centre. *Sub-metacentric chromosome – the centromere is in intermediate position. *Acrocentric chromosome – centromere is close to the end. *Telocentric chromosome – centromere is located at the terminal end.
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- 11. *Chromosomes in humanscan be divided into 2 types- autosomes & sex chromosomes. *The normal human male has 46XY chromosomal constitution. *The normal human female has 46XX chromosomal constitution.
- 13. *Autosomes * Classified ÷d on basis of length & morphological similarities into 7 groups Group A : 1-3 B : 4-5 C : 6-12 D : 13-15 E : 16-18 F : 19-20 G : 21-22 X chromosome fall under group C Y chromosome fall under group G.
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- 16. *DNA (Deoxyribo NucleicAcid) •a polymer of nucleotide monomers •2’-deoxyribose sugar •Four bases: •Adenine, A •Guanine, G •Thymine, T •Cytosine, C Sugar part Base part
- 17. *Genes *A gene: DNAsequence that is needed to encode amino acid sequence of a protein *They contain the hereditary information encoded in their chemical structure for transmission from generation to generation.
- 18. *Inheritance is howtraits, or characteristics, are passed on from generation to generation. *Dominant traits- traits that are expressed. *Recessive traits- traits that are covered up. *Alleles- the different genes for the same trait. *Genotype- the types of genes (Alleles) present.
- 19. *Phenotype- physical appearance resultingfrom gene make up. *Locus – location of a gene/marker on the chromosome. *Homozygous- two of the same alleles. *Heterozygous- two different alleles.
- 20. *GENETIC DISORDERS *CHROMOSOMAL DISORDERS *SEX-LINKEDSINGLE GENE DISORDERS *MULTIFACTORIAL & POLYGENIC DISORDERS
- 21. *Chromosomal abnormalities Chromosomal abnormalities Numerical (aneuploidy) Autosomal Sex chromosomal Structural DeletionsDuplications Translocations Monosomy Trisomy Polyploidy
- 22. *MUTATIONS/ ABERRATIONS *Mutations aresudden genetic change (primary nucleotide sequence of DNA) Harmful mutations- less able to survive results genetic disorders e.g., Cancer. Beneficial – results in genetic variations Neutral *Exposure to UV rays , radiations & chemical carcinogens
- 23. *Structural aberration ofchromosomes *Deletion:- the segment of chromosome is lost after breakage. e.g., Cri-du-chat syndrome (deletion of short arm of chromosome 5). *Duplication:- a portion of the chromosome is duplicated. e.g., Charcot marie tooth disease.
- 25. *Inversions:- a portionof the chromosome has broken off, turned upside down & reattached. *Insertions:- a portion of one chromosome has been deleted from its normal place & inserted into another chromosome
- 26. *Translocation:- There isaberrant re-joining of the broken segments occurring on 2 chromosomes. There is exchange of segments between 2 non-homologous chromosomes. E.g., Down syndrome occurring due to translocation between chromosome 14 & 21. Philadelphia chromosome an acquired translocation occurring b/w 9 & 22 chr. seen in pts with CML.
- 28. *Single gene disorders *Theseoccur due to mutation in either one or in a pair of homologous alleles at a single locus of the chromosome. *If the locus is on Autosomes it is called Autosomal(dominant/recessive) & * if on X/Y chromosome the it is called Sex- linked ( dominant/recessive).
- 34. *Multifactorial/polygenic *Resulting from acombination of genetic & environmental factors are termed multifactorial. *Those involving multiple genes are termed polygenic.