the first offspring (or filial) generation.   The next and subsequent generations are referred to as f2, f3, etc.

alternate forms or varieties of a gene.   The alleles for a trait occupy the same locus or position on homologous chromosomes and thus govern the same trait.  However, because they are different, their action may result in different expressions of that trait.

  small molecules that are the components of proteins.  There are 20 different kinds of amino acids in living things.  Proteins are composed of different combinations of amino acids assembled in chain-like molecules.  Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.

a rare genetically inherited form of mental retardation due to the deletion or inactivation of specific genes on chromosome 15.  The inheritance of this syndrome is subject to genome imprinting.  Children with Angleman syndrome typically also have small heads, experience seizures, have pronounced speech impairment, are hyperactive, and have [..]

an incorrect 19th century theory about the inheritance of characteristics.  It proposed that inherited traits blend from generation to generation.  Through his plant cross-breeding experiments, Gregor Mendel proved that this was wrong

an individual who is heterozygous for a trait that only shows up in the phenotype of those who are homozygous recessive.  Carriers often do not show any signs of the trait but can pass it on to their offspring.  This is the case with hemophilia.

an impairment of vision caused by the lenses of the eyes becoming cloudy.  Cataracts are common in elderly people.  They may be inherited or caused by diabetes and environmental factors.

an illness that lasts for a long period of time or indefinitely.  In contrast, an acute disease is one with a rapid onset and a short but usually severe course.

  the situation in which two different alleles for a trait are expressed unblended in the phenotype of heterozygous individuals.  Neither allele is dominant or recessive, so that both appear in the phenotype or influence it.  Type AB blood is an example.  Such traits are said to be codominant.

the mating of two genetically different plants of the same species.  Usually, the term is used in reference to the crossing of two pure breeding (homozygous) plants.