During cleavages, differnt cleavage furrows may divide the egg from different planes. Few important cleavage planes are following: 1. Meridional plane- When cleavage furrow passes through the centre of animal-vegetal axis and bisects the both poles of the egg, then such plane of cleavage is called meridional plane, e.g., Rana pipiens, Lepidosteus osseus and first [...]
The rate of cleavage varies from species to species. For example, in the gold fish, divisions follow each other continuously at regular intervals of 20 minutes. The inter-cleavage interval of frog is one hour and of mouse is 10 to 12 hours. In most of these cases, the cleavage rate remains rapid (synchronous) during completion [...]
Though, the mitosis involved in cleavage and the mitosis occurred in late embryos and in adult animals, is fundamentally same, but, both differ in following aspects: 1. In the later embryonic stages and in the adult, the mitosis is intimately connected with growth. After each mitotic cell division the daughter cells grow and when they [...]
The process of cleavage could be noticed to be operative in animal eggs, only in the eighteenth century, when, in year 1738 first of all Swammerdam observed the first cleavage of the frog’s egg. In 1780, Spallanzani described first two cleavage planes of egg. Prevost and Dumas in 1824, made extensive observations on the cleavage [...]
This is the inherent nature of the sexually reproductive multi-cellular animals that their body originates from a large-sized, single celled (unicellular), nutrient-filled, diploid and fertilized egg or zygote. In them, immediately after the activation of egg either through the intervention of a spermatozoon (fertilization) or through some parthenogenetic agent (parthenogensis), the activated egg is passed [...]
On the basis of shape the proteins may be of- (i) Fibrous protein- when the axial ratio of length : width of a protein molecule is more than 10, it is called a ‘fibrous protein’. example- alpha-keratin from hair, collagen, elastin etc. (ii) Globular protein- when the axial ratio of length: width of a protein [...]
The population which is infinitely large and formed of a group of such individuals which have the same chance of mating and producing progeny, provided they are sexually mature and of opposite sex. Panmictic units are integrated into the more or less complex systems of populations composing the species.
The sum total of all different alleles in the breeding members of a population at a given time is known as gene pool.
The proportion of one particular type of allele to the total of all alleles at this genetic locus in a breeding population is known as gene frequency or allele frequency. The proportion of frequency of any particular genotype among the inviduals of a population is known as genotype frequency. If any population of 200 individuals [...]
The principle that both gene and genotype frequencies will remain in equilibrium in an infinitely large population in the absence of mutation, migration, selection and non random imating.
Dr. Amlan Kumar Mitra, Biology Guide Since 2009
