subject: The Basics Of Human Genetics [print this page] The human genome refers to the whole genes of an individual. This includes the DNA, RNA, chromosomes, proteins and metabolites. Within the genome are structures of chromosomes in long double strands, which contain the DNA. Each human being has 23 pairs of chromosomes. Half of each pair is inherited from the person's father, while the other half of the pair is inherited from the person's mother. Of the 23 chromosomes, 22 of them are autosomes, while the remaining pair is composed of the sex chromosomes X and Y. The sex chromosomes determine the sex or gender of an individual. A normal male has and XY chromosome, while a normal female has XX chromosomes.
The nucleus is where the chromosomes are located. The DNA of each chromosome is arranged into several subunits-referred to as gene-of genetic information. The genes are composed of nucleotides, which have phosphates, sugar, and nitrogen-containing base. In the DNA are four bases named as adenine, guanine, thymine and cystosine. An individual's uniqueness is determined by the difference in the arrangement of the four bases on each DNA strand. The said arrangement is crucial in producing the RNA, which produces the protein.
The genetic identity of an individual is determined by that person's genotype-genes particularly combined in their cells, and the result is not shown in the physical appearance of that individual. It is the phenotype-the physical expression of the genotype-that defines the person's physical traits and characteristics including the color of the eye, hair, and skin. Every genotype is different, which makes each human different. While the human genotypes are similar in many ways, there are small differences, called polymorphisms that make each individual unique in appearance and genetic composition.
The genetic polymorphisms are crucial in identifying humans as individuals. Nonetheless, at times, the polymorphisms are related to an illness or inability to break down drugs in a normal way. Such type of polymorphism is called genetic mutation or variation, and can be inherited or spontaneous. Not all genetic mutations are bad and can lead in a disease. Sometimes, the mutation happens in an attempt by a human body to protect that body from an illness, and in so doing, result in developing a certain disease such as the cystic fibrosis. It could also be that only one gene is different, and thus, termed as single nucleotide polymorphism.
Genetic variation can happen in many ways, however, they all lead to transmission of a polymorphism from one person to the next generation. The autosomal dominant is a type of transmission in which a single copy of a gene in the autosomal chromosomes can be adequate to make a certain trait appear like an eye color or a disease.
Another way of transmission is autosomal recessive, which requires two copies of similar genes-one from mother and another from father-for a certain trait or illness to appear. There is also the X-linked recessive transmission in which the genetic variation resides on either X or Y chromosome, and can only affect either a female or male.
Genetic testing examines the DNA of the person to determine what cause a certain disease or whether a person carries a particular gene variant that can develop into a disease. If there is any presence of such genetic variation, the individual or genetic counselor may try to find out the chances of passing such genes to another generation.
