Biology 42
Crossing Over
Definition : The process of exchange of genetic material between two non-sister chromatids of homologous chromosomes is called Crossing over. Introduction : If independent assortment takes place ( when genes are located on different chromosomes), we expect a test cross of ratio 1 : 1 : 1 : 1 Fig. : Showing Crossing over […]
Coupling and Repulsion phases
Definition : Alleles coming from the same parent tend to enter the same gamete and are together in most cases. This phenomenon called coupling similarly, genes coming from different parent tend to enter different gametes and to be inherited separately – independently in most cases. This phenomenon is called Repulsion. Introduction : When two […]
Linkage
Definition : The genes located on sa the e chromosome are said to be linked genes, they remain linked together is passing referred as Linkage. Introduction : According to principle of Independent Assortment, when two or more genes are considered together, they assort (separate) randomly during distribution into gametes. But later, it was argued that Mendel […]
Pedigree Analysis
Definition : Pedigree analysis is a method, through which, we can study the record of the occurrence of a trait in several generations of a human family. Introduction : ( Pedigree analysis helps in identification of the disease or a particular trait from the roots ) It is quite easy to identify same forms of inheritance from […]
Co – Dominance
Definition : hen both dominate and recessive characters express incompletely in F1 hybrid, as the dominant character is unable to suppuess recessive character. This phenomenon is called Co – dominance. Introduction : In co-dominance, a dominant character is unable to suppress recessive character and both of them are expressed incompletely in an F1 hybrid. In […]
Polyploidy
Definition : Variations in which the number of chromosome sets (n) is greater than the diploid number (2n). For example triploidy (3n) and tetraploidy (4n) Introduction : The most widespread and distinctive cytogenetic process of speciation in higher plants is polyploidy, the multiplication of entire chromosomal complements. Subtitle 1 : Polyploidy has been of such overriding […]
Speciation
Definition : “Origin of new species from pre- existing ones” Introduction : Speciation is an evolutionary event, which occurs when gene pool of a population is reproductively isolated from other populations of parental species and no longer gene flow occurs between them. There are certain mechanisms that operate in formation of new species (Isolating mechanisms) […]
Post – Mating Mechanism
1) Gametic Mortality : Occurs when sperm may fail to fertilize the egg and both of them perish. A male with non-functional gonads but with normal sex behavior may induce a female to layeggs but soon die. This phenomenon was observed in toad – Bufo fowleri and B. Vallicep. 2) Zygotic Mortality : In this type, gametes […]
Premating Mechanism
Geographic Isolation : It plays an important role in allopatric isolation. In geographic isolation, two populations of same species are separated by some physical or geographical barrier or they occupy different geographic areas. The barriers may be maintained ranges, desert, thick forests, land bridges or water bodies etc. Because of these barriers individuals of these […]
Isolating Mechanism
Definition : Segregation of a population of a particular species by certain mechanisms, which prevent interbreeding among them, leads to Formation of a new species. Such mechanisms called as Isolation Mechanisms. Introduction : “Species” Latin word- meaning kind or appearance. A species exist in nature as discrete units – demarcated from other species. The biological species concept defines […]
Chromosomal Mutations
Definition : Mutations which results in changes in the structure of individual chromosomes or results in changes in the number of chromosomes, named as chromosomal mutations. Introduction : Changes in the structure of chromosomes can take place, due to loss of one or more genes viz. election or duplication arrangement of genes viz. inversion or may occur […]
Coagulation – Cessation of bleeding
Blood coagulation or Hemostasis is the cessation of bleeding from a cut or several vessels. When blood is shed, it loses fluid nature in a few minutes and sets into a semisolid jelly. This phenomenon is called coagulation or clotting. On holding back, the clot retracts to a smaller volume and presses out a clear straw colored fluid called the Serum. Serum does not clot any further.....
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