Extensions of Mendelian Genetics
In incomplete, or partial, dominance, no one allele is dominant.
Multiple alleles of a gene may exist in a population.
Tay-Sachs disease (http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?272800) is a human disorder that illustrates the principle of incomplete dominance. Extensive information on the biochemical basis, molecular genetics, allelic variation, and further references are found on this page.
Lethal alleles may be recessive or dominant.
- ABO blood group primer
What's your type? (http://sln.fi.edu/biosci/blood/types.html) is a primer to the ABO blood groups and a brief guide to the basics of Rh factor. It has a neat animated gif of a beating heart.
- Blood group incompatibilities
Blood group incompatibilities (http://www.ohsu.edu/cliniweb/C20/C20.188.html) provides links to disorders caused by maternal fetal incompatibility of Rh type.
Phenotypes are often controlled by more than one gene.
FlyBase (http://flybase.bio.indiana.edu/) contains references to many alleles that are lethal in Drosophila.
- Genetic Testing for Hungtinton's Disease
Genetic Testing for Hungtinton's disease (http://www.hdsa.org/) is a guide to the presymptomatic testing for this fatal disease. This site provides a brief overview of the test, a discussion of the difficulty of the decision to be tested, and a list of testing centers by state.
- Huntington's Disease
Huntington's disease (http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?143100) is a comprehensive listing of the biochemistry and genetics of this disease.
X-linkage describes genes on the X chromosome.
- Epistatic Genes
(http://www.blc.arizona.edu/courses/181gh/rick/genetics3/epistasis.html) This site uses the example of coat color in mice and cats to demonstrate epistasis.
Phenotypic expression is not always a direct reflection of the genotype.
- Lesch-Nyhan Syndrome
The genetics, biochemistry, and clinical indications for Lesch-Nyhan syndrome (http://www.icondata.com/health/pedbase/files/LESCH-NY.HTM), an X-linked recessive disorder, are available at this site.
- Lesch-Nyhan Syndrome
The Online Mendelian Inheritance in Man entry for Lesch-Nyhan syndrome (http://www.ncbi.nih.gov/entrez/dispomim.cgi?id=300322) may be viewed at this site. It includes extensive references to this disease.
Genetic fate of purebred dogs.
- Siamese Breed FAQ
The Traditional Siamese Breed FAQ (http://www.travelswithtigger.com/fanciers/trad-siamese-faq.html) contains information on the genetics of coat color in this breed.
FlyBase (http://flybase.bio.indiana.edu/) contains references to many alleles that have variable penetrance, expressivity and exhibit position effects in Drosophila.
- Uniparental Disomy and Genomic Imprinting
Uniparental disomy and genomic imprinting (http://ahsc.arizona.edu/~msrgsn/gd/gdvol10c.htm) is a discussion of human disorders that result from the inheritance of both copies of a chromosome from one parent.
- Prader-Willi Syndrome
Prader-Willi syndrome (http://www.ncbi.nih.gov/entrez/dispomim.cgi?id=176270) is caused by the maternal inheritance of a region of chromosome 15 in the absence of the corresponding region of the paternal chromosome. This site is the official site of the Prader-Willi Syndrome Association.
- Angelman Syndrome
Angelman syndrome (http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?105830) results when this same region of chromosome 15 is contributed only by the paternal parent.
- The Dog Genome Project
The Dog Genome Project (http://mendel.berkeley.edu/dog.html) is the central site for the genetic analysis of the genome of purebred dogs. This site has information on genetic disorders of dogs as well as links to other sites for general breed information.