Medicine is transforming rapidly. During this era of human history, scientists are forever changing lives, because for the first time humans are not powerless against their genes! We now have the power to not only predict, but also alter our very future. The Genetic Revolution is here!
With the power of gene therapy, scientists now have a new tool that enables them to change a patient's DNA. Medical treatments usually counteract the symptoms of a disease. But with gene therapy, doctors can cure diseases. Click to learn more
The concepts described in this website might be a review for some people, or it might be a new learning experience. Click in order to learn or review the basics of biology and genetics.
Medicine is transforming rapidly. During this era of human history, scientists are forever changing lives, because for the first time humans are not powerless against their genes! We now have the power to not only predict, but also alter our very future. The Genetic Revolution is here!
Genetics- A Brief Introduction
Genetics focus on the passing of genes from a parent to a child. Depending on the gene passed, the child could receive harmless blue eyes, or a dangerous disorder. On the right is a pedigree, often used to determine the inheritance of genetic disorders in a family.
(68)
(69)
Gregor Mendel, also known as the "Father of Modern Genetics", studied seven different pea traits and their transmission in 1866. Although he had no modern knowledge of cellular and DNA mechanisms, he was able to accurately create theories for the results he was seeing:
Law of Segregation: During meiosis (the creation of eggs or sperms), alleles possessed by the parents will segregate into different gametes, each only carrying one of the factors.
Law of Independent Assortment: In the gametes, the possible combination of each alleles are equal, because each genes separate independently of another gene.
Law of Dominance: Traits are determined by two alleles (or factors), each characteristically dominant, co-dominant, or recessive. Dominant alleles will mask the expression of recessive alleles.
Genes of a sexually reproducing organism have two copies, or alleles, one on each pair. In a population, there could be more than two alleles, resulting in variation. If a cell have two sets of homologous chromosomes, they are called diploid. Haploid cells have only one set of homologous chromosomes (gametes cells).
If a human gene has two of the same alleles, then the gene is homozygous. If the alleles are different, then it is heterozygous. Dominant alleles are usually defined with a capitalized letter, while recessive alleles are usually defined with a lowercase letter.
Dominant Allele: this allele is always expressed, even if there is only one copy. For example, a gene with alleles DD and Dd will both express the dominant allele (D), while masking the recessive allele (d)
Recessive Allele: For a recessive allele to be expressed, two identical copies of the allele is necessary. For example, to express the recessive allele r, both copies of the allele is necessary: rr. Because males only have one X chromosome, only one copy of the recessive allele on the X chromosome is needed.
The X and Y sex chromosomes can carry sex linked genes. Men usually have an X and a Y chromosome, while women usually have two Y chromosomes. Because of this, only men can inherit Y-linked traits, but both men and women can inherit X-linked traits.
A diagram showing mitosis, which creates two diploid cells
(70)
A diagram showing meiosis, which creates four haploid cells. Notice that the first three rows of the process are very similar to mitosis.
(71)
A picture showing the X and Y chromosome. The larger of the two chromosomes is the X chromosome.
(72)
(73)
(74)
(75)
(76)
When a single gene produces multiple, different, and unrelated phenotypic traits, it is called pleiotropism, or pleotrophy. This is caused by gene products, which are active in many different places in the body. One example of this disease is Marfan's syndrome.
Genes that mask the phenotypic traits of other genes are called epistatic genes. The gene that is "masked" is called the hypostatic gene. Some individuals may inherit dominant genes that cause diseases, but there may only be partial symptoms because of epistatic genes. Individuals with nonpenetrance, shows no expression of the diseased gene, but because they still have the mutated gene, they can pass the gene down to their offspring.
There are also traits which are multigenic, because they are effected by several genes. A common example is the color of the human eye, which can be affected by at least three different genes.
Somatic mosaicism is when an individual has two types of cells, one with the mutation and another without it. Humans are created from one fertilized egg, made up of one cell. When the cell divides, usually every "daughter cell" has the same DNA as the original single-cell egg. Suppose that during a two-cell stage (the fertilized egg cell had divided once, so there are only two cells), one of the cells develop a mutation, while the other cell does not. As the two cells divide and develop, half of the cells in the body would have the mutation, and half would not. This is the common explanation for people with two eye colors.