Ethidium bromide is the dye used for visualising the DNA. Since it can exchange the visible range of wave length with the invisible wave length of DNA so that it makes it visible under UV light.

The primary transcript consists of introns and exons. "Presence of introns is reminiscent of antiquity" implies that introns were previously in past an important pieces of information used to form mRNA but now are of no importance.

"Process of splicing represents the dominance of RNA world" implies that RNA is the one that decides whether to keep introns or not, DNA kept the both

The phenotypic ratios are the ratios of visible characteristics. The genotypic ratios are the ratios of gene combinations in the offspring, and these are not always distinguishable in the phenotypes. The term "phenotype" refers to the observable physical properties of an organism; these include the organism's appearance, development, and behavior. An organism's phenotype is determined by its genotype, which is the set of genes the organism carries, as well as by environmental influences upon these genes. Phenotypic ratio pertains to the relative number of offspring manifesting a particular trait or combination of traits. It can be determined by doing a test cross and identifying the frequency of a trait or trait combinations that will be expressed based on the genotypes of the offspring. 

The genotypic ratio shows the number of times a characteristic of an organism will be seen in the offspring when genes for certain traits are crossed. ... The genotypic ratio for this cross is written 1:2:1. In animals and plants, each gene has 2 alleles or variations, one from each parent. An organism's genotype is its specific combination of alleles for a given gene. So, for example, in the pea plants above, the possible genotypes for the flower-colour gene were red-red, red-white, and white-white. The phenotype is the physical manifestation of an organism's allelic combination (genotype). 

Hence, the term "phenotype" refers to the observable physical properties of an organism; these include the organism's appearance, development, and behaviour. An organism's phenotype is determined by its genotype, which is the set of genes the organism carries, as well as by environmental influences upon these genes.

Endometriosis is a condition in which cells similar to those in the endometrium, the layer of tissue that normally covers the inside of the uterus, grow outside of it.

During the mid cycle Leutinizing hormone secretes to its maximum level which induces rupture of Graafian follicle and thereby the release of ovum (ovulation). The ovulation is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum which secretes large amounts of progesterone which is essential for maintenance of the endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy.

A human sperm cell consists of a flat, disc shaped head 5.1 µm by 3.1 µm and a tail 50 µm long. The tail flagellates, which propels the sperm cell (at about 1–3 mm/minute in humans) by whipping in an elliptical cone. Structurally the spermatozoa of the head, the middle piece and the flagellum. The head has a highly condensed haploid nucleus, surrounded by a thin layer of cytoplasmic material, which is covered in a cap-like fashion by the membrane limiting the acrosome. The head contains the genetic material for fertilisation in a haploid nucleus. The acrosome in the head contains enzymes so that a sperm can penetrate an egg. The middle piece is packed with mitochondria to release energy needed to swim and fertilise the egg. The tail enables the sperm to swim.

• Fertilization performs two basic functions in the process of embryonic development:

(a) Upon fertilization, the secondary oocyte completes meiotic division and produces a second polar body, which degenerates.

(b) A diploid zygote is formed, which undergoes cleavage to form a morula and then a blastocyst, which implants in the endometrium.

• Chemical events that occur during fertilization are as follow: 

1. Approximation of sperm and ovum: This can be done by fertilizin-antifertilizin compatibility reaction. Fertilizin which is a glycoprotein of egg interacts with the antifertilizin i.e., composed of acidic amino acids of sperm of the same species which results in making the sperms stick to the egg surface.
2. Zona lysins are proteolytic enzymes that are capable of degrading the zona pellucida, perhaps easing the passage of sperm cells through to the ovum.

• Physical events that occur during fertilization are as follows:

1. The acrosomal membrane fuses with the plasma membrane of the sperm cell.
2. The enzymes within the acrosome are released into the milieu surrounding the sperm and egg.
3. Activation of ovum: As sperm enters the ovum (actually a secondary oocyte) it gets activated and undergoes the second meiotic division. As a result of this, the oocyte produces an ovum and a secondary polar body. The polar bodies ultimately degenerate and the ovum contains the haploid number of chromosomes. As the sperm cells approach the egg, the acrosome reaction occurs to prepare the sperm to fertilize the ovum (called capacitation). 

Cleistogamous flowers do not open whereas chasmogamous flowers open.

Cleistogamous flowers can only carry out self-pollination whereas chasmogamous flowers are usually cross-pollinated (and sometimes self-pollinated)

In cleistogamous flowers, reproductive structures are often smaller and less pollen needs to be produced as compared to chasmogamous flowers.

Cleistogamous flowers are non-showy and inconspicuous whereas chasmogamous flowers are showy and highly conspicuous.

Cleistogamous flowers are homogamous whereas chasmogamous flowers are usually dichogamous.

Cleistogamous flowers do not need any agents for pollination whereas chasmogamous flowers are dependent on pollination agents since they arre usually cross-pollinated.

The effluent formed from the primary treatment by filtration and sedimentation is passed to aeration tank for secondary treatment. In aeration tank, the air is pumped with constant agitation that causes vigorous growth of bacteria. This results in the formation of floc (Bacteria + Fungal filaments).​  The organic matter is consumed by bacteria that causes decrease in BOD of sewage.
BOD is the amount of oxygen required by bacteria to oxidise all the organic matter present in the effluent. Naturally, if organic matter decreases BOD also decreases and ultimately pollution decreases. When BOD and hence pollution is reduced, effluent is passed into a settling tank. Here, flocs settle down and it is known as