Structure of Dna

Every living organism is made of cells. Every cell has a nucleus, and every nucleus has chromosomes. Human beings have 46 chromosomes or 23 chromosome pairs and each chromosome contains hundreds of genes. These genes contain the recipes, for proteins that make most of the body. Structural proteins form things such as skin, hair, and muscle. These chromosomes are very long compact coils of DNA (Deoxyribonucleic Acid) that store all the information that the body inbeds such as how one looks and functions.

This paper will first describe the structure of DNA; second discuss how the structure of DNA allows it to serve as the basis for inheritance, third examine how meiosis allows DNA to be divided into gametes and finally, describe how this relates to Gregor Mendel’s patterns of inheritance. The structure of DNA DNA is a thread formed by two strands, related together to form a Double Helix. The Double Helix looks like a twisted ladder. The “sides” of this “ladder” are long units called nucleotides and are made of three parts; a nitrogenous base, a sugar, and a phosphate group.

The sides of the ladder or the nucleotides from the two separate strands of the DNA are attached by an appendage made of one of four separate bases. These appendages represent the “rungs” of the DNA “ladder” and are attached to the complimentary strand or side of the DNA. The bases or “rungs” are made of either Adenine (A) and Thymine (T) or Cytosine (C) and Guanine (G). The attachment of the strands by the bases is specific as Adenine can only join with Thymine, and Cytosine can only join with Guanine.

Since this base pairing is specific, if one knows the sequence of bases along one strand of the DNA one will also know the sequence along the complimentary strand. DNA as a Basis for Inheritance The unique pairing of the rungs of the DNA ladder is the basis for DNA acting as the molecule of inheritance. DNA duplicates in a process called DNA replication. This process involves the separation of a DNA molecule into two different strands and starts at specific sites of the double helix called origins of replication. Each of these strands serves as a template to assemble a new complementary strand.

The result of DNA replication is two identical double-stranded molecules of DNA. This process yields a new double-helix DNA molecule consisting of a single strand of old DNA, with one single strand of a newly replicated DNA. As this process occurs, genetic instructions are inherited or passed on from one generation to the next. How Meiosis Allows DNA to be divided into Gametes Mitosis and meiosis are two types of cell division. Meiosis the topic at hand, consists of two separate divisions of sex cells. In the first division, the chromosome pairs line up side by side.

Each chromosome duplicates itself. Each doubled pair then moves to the equator. Next, the members of each original pair duplicates move to the opposite poles and the cell divides. Each of the two daughter cells receives one member of each original pair of chromosomes and it’s duplicate. These two new cells divide immediately. This time the chromosomes do not duplicate themselves. Instead, one of each kind goes to each new daughter cell. Thus the two divisions of meiosis produce four sex cells. Each cell contains half the number of chromosomes found in all the other cells of an organism.

Gregor Mendel’s pattern of inheritance Gregor Mendel, known as the father of genetics first tried to understand how traits were passed on from generation to generation. From his works on pea plants he discovered the fundamental laws of inheritance. Mendel conducted genetic experiments on pea plants from 1856-1863. As a result of his experiments he came up with three theories of heredity which are: 1/- The Law of Segregation: Each inherited trait can be defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair.

Offspring therefore, inherit one genetic allele from each parent when sex cells unite in fertilization. 2/- The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. 3/- The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant. Scientists are still using Mendel’s patterns of inheritance as basis principles. He identified the hereditary unit, genes. The principle of segregation states that during the formation of gametes, the two traits carried by each parent separate.

Mendel’s principle of independent assortment states that during gamete formation, the alleles of a gene for one trait (Tt) segregate independently from the alleles of a gene from another trait (Yy). This principle applies when a cross takes place between two individuals hybrid for two or more traits that do not exist on the same chromosome. However, if two genes are linked on the same chromosome, they will not sort independently. For example, if the gene for tall is linked to the gene for yellow seed color a tall plant will have yellow seeds. If the plant is short it will have another color of seeds.

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