Introduction to Genetics PDF

Molecular Biology and Genetics Introduction to Genetics 1 What is genetics mean? Genetics is the study of biological inheritance that explains HOW characters transmitted from parents to offspring. WHY the members of the same family (or species) possess...

Molecular Biology and Genetics Introduction to Genetics 1 What is genetics mean? Genetics is the study of biological inheritance that explains HOW characters transmitted from parents to offspring. WHY the members of the same family (or species) possess similar characteristics. 2 1  Historical View Blood theory For many centuries, it was thought “children gain their characters through receiving blood from their parents” By 1850s, The blood theory of inheritance was criticized “The semen contained no blood” What is the hereditary substance? 3 Historical View What is the hereditary substance? in 1866 Through experiments on the breeding patterns of pea plants, Mendel ensures “inheritance is controlled by certain factors passed from parents to offspring” By 1900s, Two botanists (Correns and Hugo de Vries) independently rediscovered the theories of Mendel. “ inheritance factors are closely related to chromosomes” in 1920s, Willard Johannsen introduced the term GENE that replaced the earlier terms inheritance factor or inheritance unit 4 2  Historical View What is the hereditary substance? Griffith demonstrated “the genetic material from one organism could transform the characteristics of another” (in 1928) 5 Historical View What is the hereditary substance? In 1944, Avery and his colleagues approved that the chemical basis of heredity lies in DNA, and not in other compounds like protein 6 3  Historical View What is the hereditary substance? The structure of the genetic material, DNA, was elucidated in 1952 by Watson and Crick 7 Mendel's Laws of Inheritance Mendel conducted hybridization (cross mating of some characters) experiments on the garden peas seed color seed shape, flower color flower position plant height ,………… Mendel chose peas for his experiments ……. Why???? 8 4  Mendel's Laws of Inheritance Mendel’s Experiments I. Monohybrid Cross II. Dihybrid Cross Mendel crossed pea plants (parents) of opposite trait (yellow & green seeds) and observed the progeny 9 Mendel's Laws of Inheritance Mendel’s Experiments I. Monohybrid Cross Monohybrid Cross clarified; - Trait phenotype could be Dominant or Recessive - Each trait is represented by 2 copies of hereditary factor NB. Punnett square is an important tool to determine the outcome crosses 10 5  Mendel's Laws of Inheritance Mendel’s Experiments I. Monohybrid Cross II. Dihybrid Cross Cross pea with opposite TWO traits 11 Mendel's Laws of Inheritance Mendel’s Experiments II. Dihybrid Cross Cross pea with opposite TWO Dihybrid Cross clarified; traits - A pair of traits segregates independently of another pair during gamete formation i.e. A pair of traits does not get inherited together, but Every trait distributed and passed from generation to the next independently from other trait. 12 6  Mendel's Laws of Inheritance Based on the results of two type experiments, Mendel puts laws of inheritance 1- Law of Dominance (1st law); hybrid offspring will only inherit the dominant trait in the phenotype. 2- Law of Independent Assortment (2nd law); a pair of traits segregates independently of another pair during gamete formation. 3- Law of Segregation (3rd law); during the production of gametes, two copies of each hereditary factor segregate so that offspring acquire one factor from each parent. 13 Count the phenotype of 2nd progeny result from crossing two pea plant one with Green (G) Inflated (I) pods and the other Yellow Constructed pods. Refer to the image and use Punnett's square Activities ---- ---- ---- ---- ---- ---- ---- ---- 14 7  Many human traits (or diseases) follow Mendel’s laws Mendelian Inheritance But there are traits (or diseases) doesn't Non-Mendelian Inheritance 15 Genetic Terms Homozygous - Locus; the specific gene location on a particular chromosome - Allele; Each gene has two alleles (one per chromosome). - Homozygous; refers to the two alleles being identical. - Heterozygous; refers to the two alleles are different. - Phenotype; the observable traits of the individual. - Genotype; the genetic composition of the individual. - Autosomal; refers to chromosomes other than sex chromosomes. - Sex chromosomes; refers to sex determining chromosomes (X & Y). - Dominant trait; one that manifests itself even in a heterozygous state. - Recessive trait; one that manifests only when in a homozygous state. - Sex-linked trait; when the allele is located on the X chromosome. 16 8 17 9