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introduction to genetics
1. The document discusses principles of genetics including concepts like heredity, variation, Mendelian genetics, and branches of genetics like cytogenetics and molecular genetics. 2. It summarizes Gregor Mendel's experiments with pea plants from 1856-1863 which led to his principles of segregation, independent assortment, and dominance and the rediscovery of his work in 1900. 3. Key genetics terminology is defined including genes, alleles, genotype and phenotype, and symbols and concepts used in pedigrees like dominant/recessive alleles and Punnett squares are explained.
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introduction to genetics
- 1. Principles of genetics ToBSc Nursing/BMIT first year Dr. Laxman Khanal Associate professor, Department of anatomy, BPKIHS 26-12-2019
- 2. Objectives: • Concepts ofgenetics • Gregor Johann Mendel: the father of genetics • Rediscovery of Mendelian concepts of genetics • Branches of genetics • Terminologies in genetics • Pedigree: definition and concept • Pedigree: symbols
- 3. Genetics: study ofheredity and variations Engravings in Babylonia (modern day Iraq) dating back at least 6000 years show pedigrees documenting the transmission of certain characteristics of the horse’s mane.
- 4. Genetic: study ofHeredity and Variation of inherited character. Heredity: tendency of offspring to resemble their parents. Variation: tendency of offspring to vary from their parents.
- 5. Modern branches ofgenetic • Cytogenetics • Molecular genetics • Phylogenetic • Developmental genetics • Behavioral genetics
- 6. Gregor Johann Mendel(1822-1884) • Was an Austrian monk. • Known as ‘father of modern genetic’. • Does the experiment in pea plant from 1856- 1863 (7 year). • These experiment lead to three principles: a. Law of segregation b. Law of independent assortment c. Law of dominance • Dies as an unrecognized man. His studies remain in dark for 34 years until rediscovery.
- 7. In year 1900:three botanist from Europe realize that Mendel had in fact studied the heredity of specific characters as they pass from parent plant to the offspring.
- 8. Terminologies: • Genetic: byWilliam Bateson (1905) • Gene: by Johanson (1909) Gene is heredity determining factor, which consists of segment of DNA located in specific position of chromosome called locus. • Allele: alleles are alternative form of gene which occupy identical loci of homologous chromosome and control the contrasting character of same trait. • Usually exists in two form: dominant allele and recessive allele
- 9. Terminologies: Dominant and recessiveallele • Dominant allele always expresses itself. • Recessive allele expresses only in absence of dominant allele. • Dominant allele suppresses or mask the expression of recessive allele. • Dominant allele usually expressed in capital letter and recessive in small letters. Example: • Height (trait) has two characters (tall and short) with tall character (T) being dominant over short (t) character.
- 10. Terminologies: Genotype and phenotype •Genotype is the genetic makeup/constitution of the organism. • Phenotype is the physical feature/appearance of the organism • Phenotype is the expression of genotype. • Pehenotype= genotype + environmental factors Example: • Height (trait) has two phenotypes (tall and short) expressed by genotype (TT, Tt & tt)
- 11. Terminologies: Homozygous, heterozygous andhemizygous • Homozygous: If both the member of allelic pair in homologous chromosome are identical. e.g. tall (TT); short (tt) • Heterozygous: If both the member of allelic pair in homologous chromosome are not identical. e.g. tall (Tt) • Hemizygous: when genes are present in only one copy. e.g. genes of X chromosome and Y chromosome of male
- 12. Hybridization and hybrid •Process of crossing two genetically different individuals. • Progeny of hybridization is called hybrid. Monohybrid cross: Tall (TT) × short (tt) Dihybrid cross: yellow & round (YYRR) × green & wrinkled (yyrr)
- 13. P generation F1generation Tall F1 generation F2 generation 3:1 Parent plant Parent plant Offspring plant Offspring plant Law of Dominance Law of Segregation
- 14. RRYY rryy RrYy RY rYRy ry RY RRYY RrYY RRYy RrYy rY RrYY rrYY RrYy rryy Ry RRYy RrYy RRyy Rryy ry RrYy rrYy Rryy rryy Yellow: Round: 9; wrinkled: 3 (9:3) Green: Round: 3; wrinkled: 1 (3:1) Law of independent assortment Gamets: 1. RY 2. rY 3. Ry 4. ry = (3:1) Alleles for separate traits are passed independently of one another.
- 15. Punnett square: This givesus the predicted frequency of all of the potential genotypes among the offspring each time reproduction occurs Y Y g g One parent Other parent Yg YgYg Yg Offspring genetic possibilities Use for yourself ! Eg: Carriers of CF
- 16. PEDIGREE: A French termple de grue or crane’s foot. • Definition: The basic medical pedigree is a graphic depiction of how family members are biologically and legally related to one another from one generation to the next.
- 17. Two basic principles •Each family member is represented by a square (male) or a circle (female). • They are connected to each other by relationship lines. Proband: The member through whom a family with genetic disorder is first brought to attention is the proband (propositus), if affected may be called index case.
- 18. Symbols used inPedigree
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- 30. Better to follow •Draw male partner to the left. • Each generation should be in the same horizontal plane. • When possible draw siblings in birth order. • If not possible, record age. • Each generation can be identified by a Roman numerical and individual by Arabic.
- 31. Uses of PedigreeDrawing • To establish mode of inheritance. • In known mode of inheritance -To predict the risk of recurrence. -Identifying the at risk individual.
- 32. A complete pedigreeis often a work of great labor, and in its finished form is frequently a work of art. -Karl Pearson ( 1912)