How does dna determine characteristics

Like a recipe book it holds the instructions for making all the proteins in our bodies. Genes are small sections of DNA within the genome that code for proteins. They contain the instructions for our individual characteristics — like eye and hair colour.

If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? Open survey. In: Facts In the Cell. DNA provides instructions for making proteins as explained by the central dogma. A trait that disappeared in one generation could reappear, unchanged, in the next.

Mendel reasoned that since traits are inherited in a discrete form, then hereditary information must also come in discrete parcels that are passed down unchanged from generation to generation. He called these parcels of hereditary information "Elemente," and today we know them as genes. All individuals in a species have the same set of genes: in peas there is a gene for pod color, a gene for plant height, a gene for pea shape, and so on.

What makes individuals different is that a gene can have several different forms, or alleles. Thus, in peas, the pod color gene has green and yellow alleles, the plant height gene has tall and dwarf alleles, and so on.

Individuals have two copies of each gene, one inherited from each parent. How the two copies interact with each other determines an organism's characteristics. What matters is how many of which type of allele an individual gets. Mendel laid the foundation for our understanding of this business. He referred to the form of a trait that was visible in his first generation of hybrids green pods, for example as dominant.

He called the other form of the trait yellow pods, for example recessive. In pea plants, for example, the green-pod allele is dominant, while the yellow-pod allele is recessive. Only individuals that inherit two recessive alleles show the recessive form of a trait. The words in the RNA then need to be "read" to produce the proteins, which are themselves stretches of words made up of a different alphabet, the amino acid alphabet.

To understand how this all comes together, consider the trait for blue eyes. That message is then translated into the blue protein pigments found in the cells of the eye. For every trait we have--eye color, skin color and so on--there is a gene or group of genes that controls the trait by producing first the message and then the protein.

Sperm cells and eggs cells are specialized to carry DNA in such a way that, at fertilization, a new individual with traits from both its mother and father is created. Newsletter Get smart. Sign up for our email newsletter. Already a subscriber? This base-to-base bonding is not random; rather, each A in one strand always pairs with a T in the other strand, and each C always pairs with a G. The double-stranded DNA that results from this pattern of bonding looks much like a ladder with sugar-phosphate side supports and base-pair rungs.

Note that because the two polynucleotides that make up double-stranded DNA are "upside down" relative to each other, their sugar-phosphate ends are anti-parallel , or arranged in opposite orientations.

This means that one strand's sugar-phosphate chain runs in the 5' to 3' direction, whereas the other's runs in the 3' to 5' direction Figure 4. It's also critical to understand that the specific sequence of A, T, C, and G nucleotides within an organism's DNA is unique to that individual, and it is this sequence that controls not only the operations within a particular cell, but within the organism as a whole.

Images like this one enabled the precise calculation of molecular distances within the double helix. Beyond the ladder-like structure described above, another key characteristic of double-stranded DNA is its unique three-dimensional shape.

The first photographic evidence of this shape was obtained in , when scientist Rosalind Franklin used a process called X-ray diffraction to capture images of DNA molecules Figure 5.

Although the black lines in these photos look relatively sparse, Dr. Franklin interpreted them as representing distances between the nucleotides that were arranged in a spiral shape called a helix.

Around the same time, researchers James Watson and Francis Crick were pursuing a definitive model for the stable structure of DNA inside cell nuclei. Watson and Crick ultimately used Franklin's images, along with their own evidence for the double-stranded nature of DNA, to argue that DNA actually takes the form of a double helix , a ladder-like structure that is twisted along its entire length Figure 6. Franklin, Watson, and Crick all published articles describing their related findings in the same issue of Nature in Most cells are incredibly small.

For instance, one human alone consists of approximately trillion cells. Yet, if all of the DNA within just one of these cells were arranged into a single straight piece, that DNA would be nearly two meters long! So, how can this much DNA be made to fit within a cell?

The answer to this question lies in the process known as DNA packaging , which is the phenomenon of fitting DNA into dense compact forms Figure 7.

During DNA packaging, long pieces of double-stranded DNA are tightly looped, coiled, and folded so that they fit easily within the cell.

Eukaryotes accomplish this feat by wrapping their DNA around special proteins called histones , thereby compacting it enough to fit inside the nucleus Figure 8. Together, eukaryotic DNA and the histone proteins that hold it together in a coiled form is called chromatin. It is impossible for researchers to see double-stranded DNA with the naked eye — unless, that is, they have a large amount of it.

Modern laboratory techniques allow scientists to extract DNA from tissue samples, thereby pooling together miniscule amounts of DNA from thousands of individual cells. When this DNA is collected and purified, the result is a whitish, sticky substance that is somewhat translucent. To actually visualize the double-helical structure of DNA, researchers require special imaging technology, such as the X-ray diffraction used by Rosalind Franklin.

However, it is possible to see chromosomes with a standard light microscope, as long as the chromosomes are in their most condensed form.