In Mendelian inheritance

Mendelian inheritance

Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...

, a child receiving a dominant allele

Allele

An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...

 from either parent will have the dominant form of the trait. Only those that received the recessive allele from both

Zygosity

Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

 parents present with the recessive phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

. Purely Mendelian traits are a tiny minority of all traits, since most phenotypic traits exhibit incomplete dominance, codominance

Codominance

Codominance refers to a relationship between two alleles of a gene. It occurs when the contributions of both alleles at a single locus are visible and do not overpower each other in the phenotype....

, and contributions from many genes

Quantitative trait locus

Quantitative traits refer to phenotypes that vary in degree and can be attributed to polygenic effects, i.e., product of two or more genes, and their environment. Quantitative trait loci are stretches of DNA containing or linked to the genes that underlie a quantitative trait...

.

The recessive phenotype may theoretically skip any number of generations, lying dormant in heterozygous

Zygosity

Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...

 "carrier" individuals until they have children with someone who also has the recessive allele and both pass it on to their child.
These traits include:

• Ability to taste
  Taste
  Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
  
   phenylthiocarbamide
  Phenylthiocarbamide
  Phenylthiocarbamide, also known as PTC, or phenylthiourea,is an organosulfur thiourea containing a phenyl ring.It has the unusual property that it either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster...
  
   (dominant)
• Ability to smell (bitter almond-like) hydrogen cyanide
• ACHOO syndrome (dominant)
• Albinism
  Albinism
  Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
  
   (recessive)
• Brachydactyly
  Brachydactyly
  Brachydactyly , is a medical term which literally means "shortness of the fingers and toes" . The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait...
  
   (Shortness of fingers and toes)
• Wet (dominant) or dry (recessive) earwax
  Earwax
  Earwax, also known by the medical term cerumen, is a yellowish waxy substance secreted in the ear canal of humans and other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, and also provides some protection from bacteria, fungi, insects and water...
  
  
• Face freckles
  Freckle
  For other uses of the word, see Freckles .Freckles are clusters of concentrated melanin which are most often visible on people with a fair complexion. A freckle is also called an "ephelis". Freckles do not have an increased number of melanin producing cells...
  
   (dominant)
• Huntingtons Disease (dominant)
• Blood type
  Blood type
  A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells . These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system...
  
  

Some traits were previously believed to be Mendelian, but their inheritance is (probably) based on more complex genetic models, possibly involving more than one gene.