Botany

DNA: Double Helical Structure and Polymorphism

A – DNA
When the relative humidity is lowered below roughly 75%, X-ray diffraction examinations of dehydrated DNA fibres showed a new form dubbed A – DNA.
1. A—DNA is a right-handed Double Helix made up of antiparallel strands kept together by Watson—Crick base pairing, similar to B—DNA.
2. The A Helix is longer and wider than the B helix, and its base pairs are bent instead of parallel to the helix axis.
3. The puckering of their ribose units causes a lot of the structural distinctions between them. C3 is out of the plane formed by the other four atoms of the furanose ring in A – DNA, while C2 is out of the plane in B – DNA. Furthermore, the minor groove almost vanishes.
4. The A Helix’s phosphate groups bind fewer H2O molecules than the phosphates in B –DNA. As a result, dehydration favours the A-type. Furthermore, the minor groove almost vanishes.
5. The A Helix’s phosphate groups bind fewer H2O molecules than the phosphates in B –DNA. As a result, dehydration favours the A-type.

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Monohybrid and Dihybrid Crosses: Definition, Explanation, and Examples

Mono-hybrid cross explanation
Johann Gregor Mendel was an Austrian monk. He made a number of investigations with pea plants. In the garden, he found several unique features in pea plants such as Tall and Dwarf plants, Green and Yellow cotyledons, Round and Wrinkled seeds, etc. These characters occurred repeatedly creation after creation since pea plants are self-pollinated. In other words, these features were mating true. Mendel chose Garden pea as his investigational organism as it is an annual plant with well-defined characteristics and is grown and mixed easily. Mendel was fortunate in his choice of a diploid organism through many creations of natural self-generation. Gardens peas had evolved into pure lines. A single alternation in a trait was therefore indicated by a visible difference between varieties furthermore in the seven pairs of distinguishing traits.
Mendel chose to study one form that was dominant over a well-defined distinct alternative. Mendel created a hybrid by crossing two plants with opposing traits. He mixed a tall species with a Dwarf variant to get this hybrid. He got the cross seed and cultivated it separately. only tall plants came from all of the seeds when these individuals were self-pollinated. The further creation formed tall and dwarf plants in a 3:1 ratio and he achieved a similar outcome in the second creation with other contrasting features in a 3:1 ratio. Each parent had two factors in charge of every feature. They produced so the tall parent had TT and the dwarf parent had tt. There was only one factor in the gametes. The tall parent’s gamete had one T while the dwarf gamete had one t. The zygote possessed one component from each parent i.e T and t. when the gametes merged in fertilization, The first filial generation often known as the F1- generation was generated by crossing despite having one factor for tallness and one factor for dwarfness. All of the F1- generation individuals grew to be tall. In the next mixture between the F1- generation, 50% of the gametes generated by the parent had the tall factor T and 50% had the dwarf factor t. When fertilization took place among the gametes 3 types of combinations were formed i.e. as TT, Tt, and tt that is in the second filial generation 25% of the plants had both tall factors, 50% of the plants had the mixtures of both factors and 25% of the plants had both dwarf factors. In the outward appearance the tall plants formed 75% and dwarf plants 25% this is called the phenotypic ratio 3:1 though genetically there were 3 types namely homozygous tall 25%, heterozygous tall 50%, and homozygous dwarf 25%. this ratio 1:2:1 is called a genotypic ratio. As only one trait was taken into account it is referred to as the monohybrid ratio

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Agriculture Biofertilizers: Types, components, and Importance

Importance of Biofertilizers
1. It is low-cost cost, easy technique, and easily available to marginal farmers.
2. It is free from pollution hazards and increases soil fertility
3. On application of Algal biofertilizers Rice yield may increase up to 55%
4. Biofertilizers increase Physiochemical properties of soil such as soil texture, cationic exchange capacity, and PH of the soil
5. Cyanobacteria secrete growth-promoting substances like NAA, IAA, Amino acids, Vitamins, etc.
6. Biofertilizers boost plant yields and soil texture, and pathogens are unable to thrive in their presence.
7. Even in semi-arid environments, biofertilizers have been found to be advantageous since they eliminate several harmful chemicals from the soil that could cause plant illnesses.

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Bacteria: Asexual Reproduction and Genetic Recombination (Parasexuality)

Sexual Reproduction in Bacteria
Sexuality in bacteria was first discovered by Tatum and Lederberg in 1947 in Escherichia coli. Gamete production and fusion are not present in bacteria. The only thing which happens in bacteria is genetic recombination. It means variation is there that does not involve gamete formation. Thus sexual reproduction in bacteria occurs by a method called Parasexuality. As a result, bacteria do not have true sexual reproduction; instead, genetic recombination occurs.
Genetic Recombination (Parasexuality)
There is no gamete formation, no gametic fusion only there is genetic recombination present in bacteria. Thus there is the transfer of genetic material from one bacteria to another bacteria, this method of genetic recombination is known as Parasexuality.

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Angiosperms: Salient Features and Dicots verses Monocots

Angiosperms: Salient Features
1. They occur in ultimate environments on the earth
2. They are covered seed-bearing plants
3. Herbs, Shrubs, Trees, Twiners, Trailers, and Climbers among others make up the sporophytic plant body
4. The Gametophytic phase is highly contracted and only represented by a few cells. The free-living existence of gametophytes is absent
5. vascular tissue is well developed, xylem and phloem are present. The xylem contains tube-like structures that are vessels, tracheids, xylem parenchyma, and xylem fibers. Phloem contains a tube that is a sieve tube, companion cells, Phloem parenchyma, and Phloem fibers

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Ovule: Structure, Types, and Embryo sac

Embryo sac and its Development
The first cell of the female gametophyte is the functional megaspore. It grows largely along the micropyle-chalazal axis and is mostly chalazal. The nucleus undergoes three mitotic divisions and forms eight nuclei. Out of the Eight nuclei, 4 are present at the micropylar end and 4 at the chalazal end. One nucleus from each group comes in the center to form 2 polar nuclei. The remaining three nuclei at the micropylar end make up the egg apparatus, whereas the remaining three nuclei at the chalazal end make up three antipodal cells. The mature female gametophyte or embryo sac is the entire structure with two polar nuclei, three antipodals, one egg, and two synergids. the Monosporic 8- nucleate embryo sac or polygonum type of embryo sac arises from a single megaspore and has 8 nuclei

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Pollination: Definition, Types, and Agents

Pollination:Definition
Pollen grains are transmitted from the Anther to the Stigma during pollination. When pollen grains land on ovule, it is known as Direct pollination e,g Gymnosperms, and some primitive Angiosperms. When pollen grains land on Stigma and form a pollen tube it is known as Indirect pollination e,g Angiosperms. Pollination’s function in fruit and seed production has been recognised since ancient times. The Arab and Assyrian kings used to perform a special religious ceremony in which the female inflorescence of the date palm was touched by the male inflorescence to ensure good fruiting. However, Thomas Millington, towards the end of the 17th century, provided the scientific underpinning for this method.

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Flower: Definition, Types, and Functions

Types of Flower
1. Complete Flower: If all the four whorls are present in the flower it is called Complete Flower (Gynoecium, Androecium, corolla, calyx).
2. Incomplete Flower: If any one of the four whorls are absent in Flower it is called Incomplete Flower (Gynoecium, Androecium, corolla, calyx)
3. Bisexual Flower: If a flower contains both male and female reproductive parts it is called Bisexual Flower.
4. Unisexual Flower: If Flower has only one reproductive part then it is called Unisexual Flower.
Pistillate Flower: If the only female part is present
Staminate Flower: If the only male part is present i.e. Androecium the flower is called Staminate Flower.
5. Dichlamydeous Flowers: If a flower contains both Calyx and Corolla it is known as Dichlamydeous Flower. It is most common in plants.
6. Monochlamydoeus Flower: If a flower contains only one whorl, the whorl which is present is known as perianth and this is seen in the case of monocot families e,g Liliaceae
7. Achlamydeous Flower: If Calyx and Corolla are absent in flower it is called Achlamydeous Flower.

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