January 2022

Linkage and crossing over: Definition, importance, and Examples

Crossing over Definition
At the tetrad phase, the improvement of novel mixtures because of section transfer with the aid of using non-sister chromatids of homologous chromosomes is referred to as crossing over
Factors that affect crossing over
1. Temperature: High and low temperatures increases the frequency of crossing over
2. Radium rays: This increases cross-over as well
3. Age: Older women have a higher likelihood of crossing over
Importance
1. It is used to generate linkage maps or genetic maps
2. Crossover produces recombinations or novel mixtures which adjust the genetic pool with the aid of using converting gene frequency and subsequently offer a pathway for evolution.

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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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