Introduction to Mendelian Genetics

Introduction to Mendelian Genetics for beginners

1. Introduction to Mendelian Genetics Presented by: Dr Anukriti Nigam Fergusson College (Auto.) Pune Prepared by: Dr Anukriti Nigam

2. Introduction Father of genetics- Gregor Johann Mendel(1822-1884). Mendel’s predecessors – Lamarck-Inheritance of acquired characters. Charles Darwin-Pangenesis theory. Naudin and Goss-Systematic experiments in plant hybridization. Mendel’s work was recognized in year1900 after independent rediscovery by three scientists – Carl Correns in Germany Hugo de Vries in the Netherlands and Erich von Tschermak-Seysenegg in Austria. Prepared by: Dr Anukriti Nigam

3. Terminology Allele – One alternative form of a given gene pair. Tall and dwarf are the alleles for the height of a pea plant. Homozygote – An individual which contains only one allele at the allelic pair. For example DD is homozygous dominant and dd is homozygous recessive. Heterozygote – An individual that contains two different alleles at the allelic pair. For example the Dd is Heterozygote. Genotype – The genetic makeup or constitution of an individual with reference to the character under consideration usually expressed by a symbol (like TT, tt or Tt ). Prepared by: Dr Anukriti Nigam

4. Terminology Contd.. Phenotype – The external appearance of an individual for a particular gene example tallness or dwarfness . F1 or first filial generation – The first generation of given cross . F2 or second filial generation – The second generation which is produced by in breeding or selfing of F1 offspring . Gamete – A sex cell having Haploid set of chromosomes and produced by meiotic cell division of a diploid cell . Backcross - The cross of an F1 hybrid to one of the homozygous parents. For pea plant height, the cross would be Dd x DD or Dd x dd. Prepared by: Dr Anukriti Nigam

5. Terminology Contd.. Testcross - The cross of any individual to a homozygous recessive parent. Used to determine if the individual is homozygous dominant or heterozygous. Monohybrid cross - Cross between parents that differ at a single allelic pair (usually AA x aa ) Monohybrid - T he offspring of two parents that are homozygous for alternate alleles of a gene. Dominance - A phenomenon in which one member of a pair of allelic genes expresses itself completely or in part by suppressing the other. Prepared by: Dr Anukriti Nigam

6. Experiments with Pea Plants Seed coat colour (gray or white ) Seed shape (round or wrinkled ) Seed colour (yellow or green ) Pod colour (green or yellow ) Flower position (axial or terminal ) Pod shape (inflated or constricted ) Stem length (tall or dwarf) Prepared by: Dr Anukriti Nigam

7. Mendel's Law Of Dominance When two homozygous individuals with one or more set of contrasting characters are crossed, the characters that appear in F1 hybrids are dominant characters and they do not appear in F1 are recessive characters. CHARACTER DOMINANT RECESSIVE 1 Stem length Tall Dwarf 2 Flower position Axial Terminal 3 Pod shape Inflated Constricted 4 Pod colour Green Yellow 5 Seed shape Round Wrinkled 6 Seed colour Yellow Green 7 Seed coat colour Grey White Prepared by: Dr Anukriti Nigam

8. Mendel's Law Of Segregation The two coexisting alleles of an individual for each trait segregate during gamete formation so that each gamete gets only one of the two alleles. Alleles again unite at random fertilization of gametes. It states that when a pair of contrasting factors or genes are brought together in a heterozygote the two members of the allelic pair remain together without being contaminated and when gametes are formed from the hybrid, the two separate out from each other and only one enters each gametes. F1 plants- Tt Tt T t T t Prepared by: Dr Anukriti Nigam

9. Monohybrid Cross A cross between 2 individuals with homozygous genotypes, who have either completely recessive alleles or dominant alleles, which may result in opposite phenotype for a certain genetic trait is known as monohybrid cross. The offspring's of such homozygous individuals express the heterozygous which are passed / inherited from their parents. Prepared by: Dr Anukriti Nigam

10. Law of Independent Assortment Mendel did his experiments by following only a single character at a time. Instead, one can follow two characters at a time, to demonstrate the Law of Independent Assortment If the inheritance of more than one pair of characters is studied simultaneously the factors or genes for each pair of character assort out independently of the other pairs. These experiments use what’s called a dihybrid cross.  Testing two hypotheses for segregation in a dihybrid cross. Note that the combination of two traits gives a 9:3:3:1 ratio. Prepared by: Dr Anukriti Nigam

11. DIHYBRID CROSS In Dihybrid cross individuals which defer in 2 traits of P generation (Parent Generation) are bred for experimental purposes. One of the parent possesses homozygous dominant alleles and the other one has homozygous recessive alleles. The F1 generation produced from such genetic cross are all heterozygous for a specific trait which is being stdied . Prepared by: Dr Anukriti Nigam

12. www.nortonbooks.com/college/biology/animations/ch10a02.htm BRAIN STORMING SESSION Prepared by: Dr Anukriti Nigam

13. Thank you… Prepared by: Dr Anukriti Nigam