Genetics

DNA REPLICATION: DNA STRUCTURE, DNA-Dependent DNA Polymerase, Leading and Lagging strand

DNA REPLICATION: Definition During cell division, DNA replication occurs. It’s bidirectional, discontinuous, and semi-conservative (semi-conservative mechanism was demonstrated by Meselson and Stahl in 1958).DNA replication is a critical mechanism for an organism’s cell development, repair, and reproduction. OVERVIEW OF DNA STRUCTURE James Watson and Francis Crick established the structural model of DNA for the first […]

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DNA Packaging: Definition, Histone proteins, and Non-Histone proteins

Why is it necessary to package DNA?
The DNA is around 3 meters long and must fit into the nucleus, which is only a few micrometers in diameter. The DNA molecules must be packed into an incredibly compressed and compact structure called chromatin to fit into the nucleus. The DNA is reduced to an 11 nm fiber during the earliest phases of packaging, which represents approximately 5-6 folds of compaction. This is accomplished by packaging nucleosomes in a specific order. DNA packaging is divided into three categories.
1. The nucleosome is the first-order DNA packing.
2. Solenoid fiber is a type of second-order DNA packing.
3. Scaffold loop Chromatids Chromosome is the third order DNA packaging.

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Chromosome- Structure, Types, and Functions for Class 12th and NEET students

The Role and Importance of Chromosomes
Storage of Genetic Code: The genetic material essential for the organism’s development and growth is stored in the chromosome. A series of components called genes make up DNA molecules. Genes are regions of DNA that code for certain proteins that the cell needs to function properly.
Sex Determination: Humans have 23 pairs of chromosomes, one of which is designated as the sex chromosome. The gender of a child is determined by the chromosome passed down by the father. The child will be female if the X chromosome is passed out of the XY chromosome, and a male child will develop if the Y chromosome is passed out of the XY chromosome.
Control of Cell Division: During the process of mitosis, chromosomes check for successful cell division. The parent cells’ chromosomes ensure that the necessary information is passed on to the daughter cells that the cell needs to grow and develop properly.
Protein Synthesis and Storage: Chromosomes direct the sequences of proteins synthesized in our bodies and also keep DNA in order. The proteins are also kept in the chromosomes’ coiled shape. These proteins that are linked to DNA aid in the correct packaging of DNA.

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Mutation: Definition, Types, Effects, and Examples

Aneuploidy: It is characterized by the loss or gain of a chromosomal set. It’s a situation in which one or a few chromosomes are added or removed from the usual amount of chromosomes. As a result, the number of chromosomes in aneuploidy can differ from the number of chromosomes in the wild type.
Nullisomy, monosomy, and trisomy are three different kinds of aneuploidy.
1. Nullisomy (2n-2) is the lack of both homologous pair chromosomes. Most creatures may die as a result of these conditions.
2. Monosomy (2n-1) is the loss of one of the homologous pair’s chromosomes.
3. Trisomy refers to the addition of a second chromosome (2n+1). Trisomy includes conditions such as Klinefelter syndrome (44+XXY/XYY) and Down syndrome.

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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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