What makes genes

The marks can be passed on from cell to cell as they divide, and they can even be passed from one generation to the next. Specialized cells can control many functions in the body.

For example, specialized cells in red blood cells make proteins that carry oxygen from air to the rest of the body. The epigenome controls many of these changes within the genome.

Lifestyle and environmental factors such as smoking, diet and infectious diseases can bring about changes in the epigenome. They can expose a person to pressures that prompt chemical responses.

These responses can lead to direct changes in the epigenome, and some of these changes can be damaging. Cancer can result from changes in the genome, the epigenome or both. Changes in the epigenome can switch on or off the genes that are involved in cell growth or the immune response. These changes can cause uncontrolled growth, a feature of cancer, or a failure of the immune system to destroy tumors.

Researchers in The Cancer Genome Atlas TCGA network are comparing the genomes and epigenomes of normal cells with those of cancer cells in the hope of compiling a current and complete list of possible epigenomic changes that can lead to cancer. Researchers in epigenomics are focused on trying to chart the locations and understand the functions of all the chemical tags that mark the genome.

This information may lead to a better understanding of the human body and knowledge of ways to improve human health. Gene therapy uses sections of DNA to treat or prevent disease. This science is still in its early stages, but there has been some success.

For example, in , scientists reported that they had managed to improve the eyesight of 3 adult patients with congenital blindness by using gene therapy. In , a reproductive endocrinologist, named John Zhang, and a team at the New Hope Fertility Center in New York used a technique called mitochondrial replacement therapy in a revolutionary way.

They announced the birth of a child to a mother carrying a fatal genetic defect. Researchers combined DNA from two women and one man to bypass the defect. The result was a healthy baby boy with three genetic parents. This type of research is still in the early stages, and much is still unknown, but results look promising.

Scientists are looking at different ways of treating cancer using gene therapy. In one study, 82 percent of patients had their cancer shrink by at least half at some point during treatment.

Women with the BRCA1 gene have a significantly higher chance of developing breast cancer. A woman can have a test to find out whether she carries that gene. BRCA1 carriers have a 50 percent chance of passing the anomaly to each of their children. Scientists say that one day we will be able to test a patient to find out which specific medicines are best for them, depending on their genetic makeup.

Some medicines work well for some patients, but not for others. Gene therapy is still a growing science, but in time, it may become a viable medical treatment. An international team of researchers reveals 83 new genetic variants that affect human height. Each has a specific set of genes that is the same from person to person. One copy of each chromosome in a pair is inherited from each parent, which means that you inherit one copy of each gene from your mother and one copy from your father.

Each chromosome has a centromere at its center, which is a small structure that divides the chromosomes into two parts see figure 2. Each part is called an arm. Genes are located on the arms of the chromosomes.

Chromosomes have caps on each arm called telomeres, which help to protect the chromosomes. As you get older, your telomere caps get shorter and shorter and are less able to protect your chromosomes from getting damaged. Genes are small segments of DNA that have different functions. Many, but not all, genes make the proteins that our bodies need to function.

Some carry messages. Still others function as building materials. All organisms need proteins so that their cells can live and grow.

Each tRNA carries a three-letter sequence on one end and an amino acid on the other. Then, another helper molecule, known as a ribosome RY-boh-soam , joins the amino acids on the other end to make the protein. Scientists first thought that each gene held the code to make one protein only.

They were wrong. Using the RNA machinery and its helpers, our cells can make way more than 20, proteins from their 20, genes. It could be a few hundred thousand — perhaps a million! How can one gene make more than one type of protein? Only some stretches of a gene, known as exons , code for amino acids. The regions in between them are introns. Scientists refer to this as mRNA splicing.

The same mRNA may be spliced in different ways. This often happens in different tissues perhaps skin, the brain or the liver. Most genes have multiple switches. Different start or end sites create different proteins, some longer and some shorter.

These DNA binding sites may be far away from the gene, but still influence when and how the cell reads its message. Splicing variations and gene switches result in different mRNAs. And these are translated into different proteins. Proteins also may change after their building blocks have been assembled into a chain. Genes that are on the X chromosome are said to be X-linked.

Genes that are on the Y chromosome are said to be Y-linked. Parents pass on traits or characteristics, such as eye colour and blood type, to their children through their genes. Some health conditions and diseases can be passed on genetically too. Sometimes, one characteristic has many different forms. Changes or variations in the gene for that characteristic cause these different forms.

These two copies of the gene contained in your chromosomes influence the way your cells work. The two alleles in a gene pair are inherited, one from each parent. Alleles interact with each other in different ways. These are called inheritance patterns. Examples of inheritance patterns include:.

An allele of a gene is said to be dominant when it effectively overrules the other recessive allele. The allele for brown eyes B is dominant over the allele for blue eyes b. So, if you have one allele for brown eyes and one allele for blue eyes Bb , your eyes will be brown. This is also the case if you have two alleles for brown eyes, BB.

However, if both alleles are for the recessive trait in this case, blue eyes, bb you will inherit blue eyes.

For blood groups, the alleles are A, B and O. The A allele is dominant over the O allele. Blood group A is said to have a dominant inheritance pattern over blood group O. If the father has two O alleles OO , he has the blood group O. For each child that couple has, each parent will pass on one or the other of those two alleles.

This is shown in figure 1. This means that each one of their children has a 50 per cent chance of having blood group A AO and a 50 per cent chance of having blood group O OO , depending on which alleles they inherit.

The combination of alleles that you have is called your genotype e. The observable trait that you have — in this case blood group A — is your phenotype. If a person has one changed q and one unchanged Q copy of a gene, and they do not have the condition associated with that gene change, they are said to be a carrier of that condition.

The condition is said to have a recessive inheritance pattern — it is not expressed if there is a functioning copy of the gene present. If two people are carriers Qq of the same recessive genetic condition, there is a 25 per cent or one in four chance that they may both pass the changed copy of the gene on to their child qq, see figure 2.

As the child then does not have an unchanged, fully functioning copy of the gene, they will develop the condition.