Plant Bible

                                                                           Linkage in Drosophila In Drosophila, grey colour(G) is dominant over black colour (g) and long wing (L) is dominant over vestigial wing (l). The genes for these two characters (colour of the body and length of the wings) are linked together in the same chromosome. The linked genotypes of the parents are written as follows: Grey long-GL/GL Black vestigial-gl/gl When a fly with grey body and long wings (GGLL) is crossed with another fly having black body and vestigial wings (ggll), all the F, individuals are having grey body and long wings (GgLI). When F, male hybrid is test crossed with the double recessive parent, the F, contains only two types of individuals in equal numbers (1:1...

                                                                           Coupling and Repulsion                   Bateson and Punnet in 1906 proposed the hypothesis of coupling and repulsion to explain the later proposed linkage.  Coupling: The tendency of two dominant alleles or recessive alleles coming from the same parent tend to enter the same gamete and Coupling inherit together is called coupling. Experimental Proof for Coupling:                       W. Bateson and RC. Punnet in 1906 reported the phenomenon of coupling and repulsion (linkage) in sweet peas. A sweet pea with blue flower (B) and long pollen grains (L) is crossed with one having red flower ...

                                                ALLELIC RELATIONSHIP   Dominant and Recessive Alleles:   Whenever one of a pair of alleles can come to phenotypic expression only in a homozygous genotype, we call that allele a recessive factor. The allele which can phenotypically express itself in the heterozygote as well as in the homozygote is called a dominant factor. Upper- and lower-case letters are commonly used to designate dominant and recessive alleles respectively. Usually, the genetic symbol corresponds to the first letter in the name of the abnormal (or mutant) trait.   (a) Carriers:   Recessive alleles (such as the one for albinism) are often deleterious to those who possess them in duplicate (homozygous recessive genotype). A heterozygote may appear just as normal as th...

                                                                Modifications of root Tap root modification:   Storage roots: 1. Conical Root These are cone like, broad at the base and gradually tapering towards the apex. Example: Daucus carota. 2. Fusiform root: These roots are swollen in the middle and tapering towards both ends. Example: Raphanus sativus 3. Napiform root: It is very broad and suddenly tapers like a tail at the apex.   Example: Beta vulgaris Breathing root: Some mangrove plants like Avicennia, Rhizophora, Bruguiera develop special kinds of roots (Negatively geotropic) for respiration because the soil becomes saturated with water and aeration is very poor. They have a large number of breathing pores or pneumatophores for exchange o...

                                                                                  MENDELISM The contribution of Mendel to Genetics is called Mendelism. It includes all concepts brought out by Mendel through his original research, on plant hybridization. Genetic laws proposed by Mendel are universal to most genes in microbes, plants and animals. Mendelian genetic concepts are basics to modern geneticists. Therefore, Mendel is called the Father of Genetics.   Mendel: Mendel is the Father of Genetics. He was born in a peasant family in 1822 in Austria. He worked as a teacher. He passed his later life as an abbot. He died in 1884. Mendel was fond of gardening and fruit-culture from his boy hood. When he was working as teacher, he perform...

                                                    Theories of Meristem Organization and Function Many anatomists illustrated the root and shoot apical meristems on the basis of number and arrangement and accordingly proposed the following theories – An extract of which are discussed below. Shoot Apical Meristem: Apical Cell Theory: Apical cell theory is proposed by Hofmeister (1852) and supported by Nageli (1859). A single apical cell is the structural and functional unit. This apical cell governs the growth and development of whole plant body. It is applicable in Algae, Bryophytes and in some Pteridophytes. Histogen Theory: Histogen theory is proposed by Hanstein (1868) and supported by Strassburgur. The shoot apex comprises three distinct zones. 1. Dermatogen: It is a outermost layer. It gives rise to epidermis. 2...

                      DISCOVERY OF PHYTOHORMONES-AUXIN, GIBBERILIN, CYTOKININ                                                                     AUXIN S.NO SCIENTISTS YEAR OF IDENTIFICATION DISCOVERY 1 Charles Darwin   1880 The unilateral growth and curvature of Canary   grass (Phalaris canariensis) coleoptile to light. 2 F. W. Went 1926 The term auxin (Greek: Auxin – to Grow)   was first used by him .   3 F. W. Went 1928 Avena curvature test – he   using   Oats (Avena) coleo...