Biological inheritance

Biological inheritance is the process by which an offspring cell or organism acquires or becomes predisposed to characteristics of its parent cell or organism. Through inheritance, variations exhibited by individuals can accumulate and cause a species to evolve.

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The study of biological inheritance is called genetics, which includes epigenetics.

The description of a mode of biological inheritance consists of three main categories:

• 1. Number of involved Loci

-Monogenetic (also called "simple") - one Locus

-Oligogenetic - few Loci

-Polygenetic - many Loci

• 2. Involved Chromosomes

-Autosomal - Loci are not situated on a sex chromosome

-Gonosomal - Loci are situated on a sex chromosome

-X-Chromosomal - Loci are situated on the X chromosome (the more common case)

-Y-Chromosomal - Loci are situated on the Y chromosome

-Mitochondrial - Loci are situated on the mitochondrial DNA

• 3. Correlation genotype-phenotype

-Dominant

-Intermediate (also called "codominant")

-Recessive

These three categories are part of every exact description of a mode of inheritance in the above order. Additionally, more specifications may be added as follows:

• Coincidental and environmental interactions

-Penetrance

-Complete

-Incomplete (percentual number)

-Expressivity

-Invariable

-Variable

-Heritability (in polygenetic and sometimes also in oligogenetic modes of inheritance)

-Maternal or paternal imprinting phenomena (also see epigenetics)

• Gender interactions

-Sex-linked inheritance (Gonosomal Loci)

-Sex-limited phenotype expression (e.g. Cryptorchism)

-Inheritance through the maternal line (in case of Mitochondrial DNA loci)

-Inheritance through the paternal line (in case of Y-chromosomal loci)

• Locus-Locus-Interactions

-Epistasis with other Loci (e.g. overdominance)

-Gene coupling with other Loci (also see crossing over)

-Homozygotous lethal factors

-Semi-lethal factors

Determination and description of a mode of inheritance is primarily achieved through statistical analysis of pedigree data. In case the involved loci are known, methods of molecular genetics can also be employed.

Literature

Ruvinsky and Sampson (2001) The Genetics of the Dog; CABI Publishing, Wallingford/New York.

Srb, Owen and Edgar (1965) General Genetics; Freeman & Company, San Francisco.