Companies:  23andme  (provides kits for heritage and may offer health related kits in future)

Human genetics is the study of heredity in human beings. The human genome, the entirety of human genetic information, contains about 22,000 genes, which form the basis of human ineritance. The majority of genes act by guiding the production of polypeptide chains that form proteins. Proteins in turn make up living matter and catalyze a variety of cellular processes.

Definitions

Gene is the functional unit of inheritance and corresponds to the segment of DNA coding for a single protein.

Genome is an organism’s complete set of genes.

Locus is the site of the gene in the genome.

Allele is an alternative form of a gene. An individual who has two different alleles or alternative genes on a chromosome is said to be heterozygous for that locus. Such different alleles are the result of things like DNA mutations which can occur spontaneously or which occur when DNA is replicated. Alleles can be dominant or they can be recessive relative to each other. If an organism is heterozygous (a/A) for an allele, the dominant allele, A, will be the gene that gets expressed and shows up in the phenotype. The recessive allele, a, will only show up in the phenotype if the organisms is homozygous (aa) for that allele.

In the classical field of genetics, one begins by isolating mutants that have an interesting or unusual appearance like fruit flies with curly wings. Working backward from the phenotypes (appearance or behavior), one then determines the organism’s genotype (the specific set of alleles forming the genome of an individual). With the enormous amount of DNA information in databases today, the exploration of gene function often begins with a DNA sequence. Proteomics is the effort to identify and characterize all of the proteins encoded in an organism’s genome, including their postranslational modifications.

Parthenogenesis: is a form of asexual reproduction in which growth of embryos occurs without fertilization. It occurs naturally in many plants and in some invertebrate animal species such as nematodies, water flees, scorpians and some bees. 

Types of Genetic Polymorphisms 

Most of the genetic diversity among members of an individual species comes about through meiosis and genetic recombination. The greater the distance between two loci on a single chromosome, the greater is the chance that they will be separated by crossing-over occurring at a site between them. If two genes are reassorted in x% of gametes, they are said to be separated on a chromosome by a genetic map distance of x map units.

Short tandem repeats (STR): are particular nucleotide sequences that are repeated within a region of a DNA strand (called an STR locus). STR loci occur frequently in the human genome, and the number of repeated sequences within an STR locus varies highly from person to person. For example, one individual’s DNA may have eleven ATT repeats at a given STR locus, while another individual may have 14 at the same locus. These variations are referred to as alleles (see above) or markers, of the particular locus. Alleles are responsible for “polymorphisms” or genetic differences between individuals. No one allele varies enough to differentiate one person from another to a statistically significant degree. A particular set of alleles at multiple loci within an individual’s DNA, however, can be used to create a DNA “finger-print” unique to that individual. This mehthod of identificaiton is called “STR profiling” and is useful in many fields, including forensic science.

Hypervariable microsatellite sequence/Variable number of tandem repeat (VNTR): are repeated DNA sequences such as CACACA found in various positions (loci) in the human genome. The number of repeats can be highly variable in the population, ranging from 4 to 40 in different individuals. Because of the variability in these sequences at each locus, individuals usually inherit a different variant from their mother and father. Such VNTRs are used in forensic science to identify potential criminal suspects. When examining the variability at 5-10 different VNTR loci, the odds that two random individuals would share the same genetic pattern by chance is about one in 10 billion. More complex sequences called Minisatelites such as GATTCCTTn vs GATTCCTTn can also be repeated.

Single Nucleotide Polymorphism (SNP): The most common genetic variations in the human population are SNPs. An example is AGCT vs ACCT. By studying candidate genes and performing genome-wide linkage disequilibrium studies, scientists are trying to uncover the “causative SN”,” the SNP that alters gene function and thereby increases the risk of disease. SNPs that affect the function of crucial components of the T-cell antigen receptor (TCR) signaling pathways could have profound effects on the function of the immune system and thus the development of autoimmune diesase. Protein tyrosine phosphatases (PTPs) are particularly good candidates for carrying disease related SNPs because they are involved in preventing spontaneous T cell activation and they restrict the response to antigen by dephosphorylating and invactivating TCR associated kinases and their substrates. PTPs are also needed to revert activated T blasts to a resting phenotype.

Restriction Fragment Length Polymorphism (RFLP): An example is GAATTC vs GATTTC