Scientists are now able to explore genome with technics that allows them to cut, separate and read DNA molecule.
A DNA is a large molecule that has to be cut into smaller pieces before the reading begin. Some bacterial enzymes known as restrictive enzymes are used in the laboratory for this very purpose. They are able to cut DNA into fragments of only several hundred bases long.
The next step is electrophoresis, which is a process of moving negatively charged DNA fragments through the porous gel after an electric voltage is been applied. The smaller DNA fragments will pass faster, and after usage of a particular stain that makes them visible, scientists get a model of bands based on the size of these DNA pieces.
In the next step, they join single-stranded DNA with DNA polymerase and nucleotide bases that are chemically stained. DNA polymerase forms new DNA strand based on the one they put in and because nucleotides this enzyme use are colored, scientists are able to read a complementary sequence of the examined DNA fragment.

A human genome contains 46 chromosomes, about 3 billions of nucleotide pairs, and around 20 000 genes. Only 2 percent of a human genome is included in protein synthesis. The genome of a fruit fly contains about 14 000, a chicken genome contains approximately 17 000, while grapes have roughly 30 000 genes.

An electrophoresis is a process during which negatively charged DNA fragments move through the porous gel after an electric voltage is been applied. The smaller DNA fragments will pass faster, and after usage of a particular stain that makes them visible, scientists get a model of bands based on the size of these DNA pieces.

Effect of point mutations may result in structural changes in protein synthesis, but they can also be neutral. If a point mutation affects the non-coding area of the DNA molecule, the effect will be neutral. But, if we assume that one base is added in or deleted from a coding area of the genome, the whole nucleotide sequence after the mutation point will be changed because it is read as codons – three bases at a time and always in the same direction. This will certainly alter the order of the amino acids that form a polypeptide. However, if base substitution occurs, only one codon will be affected. Since usually more that one codon determines a particular amino acid, this mutation doesn’t have to alter the protein synthesis. Base substitution can also occur in an expressed gene and change the codon as well as the amino acid. If the mutation occurs in the active site of a protein, there is a high possibility that the effect will be harmful or beneficial. However, if the mutation happens in the other segments the effect may be neutral.

Tay-Sachs disease is an autosomal recessive genetic disorder that affects the nervous system. Since male and female are heterozygous and the carriers of the recessive allele, their future children will be affected by this illness only if they inherit recessive allele from both of their parents, which would make them homozygous recessive. The probability for a child to develop this disease is 25 percent.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}t}\
{color{Blue}T} & TT & Tt\
{color{Blue}t} & Tt & {color{Red} tt}
end{tabular}
end{center}

This particular couple may advise with a genetic counselor so he could help them to decide whether they want to conceive and to inform them about other options. If a couple decides to have a baby, chorionic villi should be sampled around the 11th week, or amniocentesis could be done around the 16th week of gestation. These procedures can tell us if the baby will develop Tay-Sachs disease or not. However, the couple could determine for the in vitro conception, where only the healthy embryos will be implanted into the mother’s uterus.