MENDELIAN INHERITANCE PRESENTED BY : ANJEEL KUMAR THAKUR Sr. Lecturer in Botany, Govt. HSS Jhiri, Jammu DATE : 24TH MAY 2018

ANJEEL KUMAR THAKUR WHAT IS INHERITANCE ? Transmission of genetic characters ( both resemblances and variations ) from parents to their children ( offspring ) is called INHERITANCE . Also known as HEREDITY VARIATION is the differences shown by the individuals of the species and offspring of the same parents Scientific study of mechanism of inheritance and the causes of hereditary variation in living organisms is called GENETICS Basic principles of genetics were discovered by Gregor Johann Mendel ( 1822-84 )

Gregor Johann Mendel 1822-1884 Austrian monk ANJEEL KUMAR THAKUR Gregor Johann Mendel Austrian monk Studied the inheritance of traits in PEA PLANTS Between 1856-63 he cultivated some 10000 pea plants Developed laws of inheritance Employed the laws of probability and statistical methods for analysis of his results Presented his findings in a paper entitled EXPERIMENTS IN PLANT HYBRIDISATION which was read before BRNO NATURAL HISTORY SOCIETY in 1865 Called the Father of Genetics But his work was not recognized until the turn of 20th century 1822-1884

Why did he choose GARDEN PEA ( Pisum sativum ) for experiments ? ANJEEL KUMAR THAKUR Why did he choose GARDEN PEA ( Pisum sativum ) for experiments ? Has a large number of VARIETIES Is ANNUAL with growth period of few months Can be grown in a SMALL AREA Produces a lot of OFFSPRING Produces pure plants when allowed to SELF-POLLINATE for several generations Can be artificially CROSS-POLLINATED Is small but flowers are large enough to be manually handled Hybrids are fertile

What were the characters of Pea studied by Mendel ? ANJEEL KUMAR THAKUR What were the characters of Pea studied by Mendel ? S.NO. CHARACTER DOMINANT TRAIT RECESSIVE TRAIT 1. HEIGHT TALL DWARF 2. FLOWER POSITION AXILLARY TERMINAL 3. COLOUR OF UNRIPE POD GREEN YELLOW 4. POD SHAPE FULL/INFLATED CONSTRICTED 5. COLOUR OF FLOWER COLOURED WHITE 6. SEED SHAPE ROUND WRINKLED 7. SEED ( COTYLEDON ) COLOUR

ANJEEL KUMAR THAKUR TERMINOLOGY TRAIT : Any characteristic which can be passed from parent to offspring HEREDITY : Passing of trait from parent to offspring GENETICS : Study of Heredity Mono hybrid cross : Cross involving a single trait e.g. Height of the plant Di hybrid cross : Cross involving two traits e.g. Form and colour of the seed

TERMINOLOGY Alleles /Allelomorphs : Two forms of a gene ANJEEL KUMAR THAKUR TERMINOLOGY Alleles /Allelomorphs : Two forms of a gene (dominant and recessive) Dominant : Stronger of the two genes expressed in the hybrid; represented by CAPITAL letter e.g. ‘T’ for Tallness Recessive : Gene that shows up less often in a cross; represented by LOWER CASE letter e.g. ‘t’ for Dwarfness Genotype : Gene combination or genetic make up of a trait (TT, Tt, tt) Phenotype : Physically expressed feature from a genotype e.g. TALL (TT, Tt) , DWARF (tt) etc. Homozygous genotype : Gene combination involving two dominant or two recessive genes e.g. ‘TT’ (homozygous or pure dominant) & ‘tt’ (homozygous or pure recessive) Heterozygous or Hybrid genotype : Gene combination of one dominant and one recessive genes e.g. ‘Tt’

ANJEEL KUMAR THAKUR MENDEL’S EXPERIMENTS WERE GROUPED DEPENDING ON THE NUMBER OF TRAITS TAKEN UNDER CONSIDRATION AT A TIME AS : CROSS TYPE NUMBER OF TRAITS UNDER STUDY MONO HYBRID CROSS ONE ( e.g. HEIGHT OF THE PLANT ) DI HYBRID CROSS TWO ( e.g. SHAPE AND COLOUR OF SEEDS ) TRI HYBRID CROSS THREE ( e.g. HEIGHT OF PLANT, SHAPE AND COLOUR OF SEED POLY HYBRID CROSS THREE OR MORE THAN THREE

ANJEEL KUMAR THAKUR MONO HYBRID CROSS

ANJEEL KUMAR THAKUR MONO HYBRID CROSS

MONO HYBRID CROSS conclusions ANJEEL KUMAR THAKUR MONO HYBRID CROSS conclusions Each organism has a large number of characters but each character behaves as a unit (PRINCIPLE OF UNIT CHARACTERS) Characters are controlled by factors and there is a pair of factors for each character. An individual receives one factor for a trait from each parent and in turn passes at random one of the two factors to each offspring (PRINCIPLE OF PAIRED FACTORS) Out of the pair of factors only one expresses itself (dominant) while the other remains unexpressed (recessive ) . The latter expresses only in homozygous state (PRINCIPLE OF DOMINANCE) The paired factors don’t mix up but remain distinct and segregate at the time of gamete formation so that a gamete receives only one factor of a character and is always pure (LAW OF SEGREGATION/LAW OF PURITY OF GAMETES) . It has universal acceptance. F2 PHENOTYPIC RATIO IS 3:1 WITH A HIDDEN RATIO OF 1 PURE DOMINANT, 2 HYBRID AND 1 RECESSIVE

ANJEEL KUMAR THAKUR DI HYBRID CROSS

DI HYBRID CROSS conclusions ANJEEL KUMAR THAKUR DI HYBRID CROSS conclusions The two factors of each character assort or separate independent of the factors of other characters at the time of gamete formation and get randomly rearranged in the offspring producing both parental and new combinations of traits. (LAW OF INDEPENDENT ASSORTMENT) F2 phenotypic ratio is 9:3:3:1

ANJEEL KUMAR THAKUR BACK CROSS : CROSS BETWEEN F1 HYBRID AND ONE OF THE PARENTS ( PURE DOMINANT OR PURE RECESSIVE ) BACK CROSS INVOLVING PURE RECESSIVE PARENT (TEST CROSS) BACK CROSS INVOLVING PURE DOMINANT PARENT (OUT CROSS) TEST CROSS RATIO TALL : DWARF 1 : 1 Any cross involving a homozygous recessive trait and an unknown genotype ( homozygous dominant or hybrid ) is known as a TEST CROSS

Why did Mendel’s work go unnoticed for some 34 years ? ANJEEL KUMAR THAKUR Why did Mendel’s work go unnoticed for some 34 years ? Published his work in an OBSCURE JOURNAL Failure of the scientists to notice his work because the scientific world was being rocked by Darwin’s theory of Evolution His ideas were ahead of his time Mendel’s failure to get the same results in Hawkweed ( Hieracium ) undertaken on the suggestion of Naegeli. It was due to non availability of pure lines Absence of aggressiveness in Mendel’s personality

REDISCOVERY OF MENDEL’S WORK ANJEEL KUMAR THAKUR REDISCOVERY OF MENDEL’S WORK Hugo de Vries of Holland, Carl Correns of Germany and Erich von Tschermak of Austria rediscovered Mendel’s work independently in 1900 Correns raised the status of two Mendel’s generalizations to the level of laws of heredity : i. LAW OF SEGREGATION ( 1st Law of Mendelism ) ii. LAW OF INDEPENDENT ASSORTMENT ( 2nd Law of Mendelism ) The other principles were called by Correns as VARIABLE PRINCIPLES

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