| Copyright © 2000-2007 Wes Harris. All rights reserved. |
Terms of Heredity - Genetics Definitions
These "terms of heredity" are provided to help people use the Advanced
Genetics Wizard.
Since there seems to be some confusion about codominance, I've provided
references
to published, scientific material to back up my use of the term.
Basic definitions of some common genetics terms are at the bottom of this
page.
Published References About Codominance
"In his law of dominance, Mendel did not accommodate different degrees of
dominance. As such examples were discovered (Bateson 1913), various
new terms were introduced. Within and between textbooks of genetics,
definitions are inconsistent. Various names have been used: partial
dominance, incomplete dominance, codominance, lack or absence of
dominance, intermediate dominance, imperfect dominance, egalitarian
dominance, and transdominance. The definitions vary from text to text and
depend on interpretation of allelic function, although an allele’s function is
seldom known and often must be assumed. In all these usages there is one
consistent aspect; each genotype has a distinguishable phenotype, and the
genotype may be inferred from the phenotype. Perhaps none of the terms
that have been used are all-inclusive, but some such term is desirable for
teaching purposes. We have chosen the term codominance as simplest,
shortest, and adequately inclusive. One can still use specialized sub-
definitions for well-analyzed cases. In our more that 20 years of teaching
this method has worked well."
BioScience Vol. 45 No. 2 Feb. 1995 pp. 98-104
Three neglected advances in classical genetics.
By Wilmer J. Miller and Willard F. Hollander
--------------------------------------------------------------------------------
"The definitions given or inferred for the intermediate form of dominance
usually require knowing the exact function of the gene. This is very seldom
known for most characters at present. All the "codominant" usages actually
show or imply 3 phenotypes for 2 codominant alleles for the monohybrid
genotypes in diploids. Why not use this consistency among names and their
usages as the single criterion and use only one name? I prefer the shortest,
codominance."
"So, for beginning students, as well as teachers and researchers, all genes
fit one of 3 categories: dominant, codominant, or recessive. When more
sophisticated nuances implying different functions are desired, then other
names can be used with a definition (please) for this next level of usage."
Brazilian Journal of Genetics
20, 4, 663-665 (1997)
By Wilmer J. Miller
Both of the quotes above were reprinted here with the permission of
Dr. Wilmer J. Miller, Professor of Genetics, Emeritus.
--------------------------------------------------------------------------------
Basic Genetics Definitions
Allele - either of the two paired genes affecting an inherited trait (one from
the father, one from the mother).
Codominant - an allele that causes the homozygous form to look different
than wild type and the heterozygous form to have traits of both. (All three
look different from each other.)
Dominant - an allele that causes the homozygous form and the
heterozygous form to look the same as each other, but different than wild
type.
Recessive - an allele that affects a animal's appearance if it's present in the
homozygous state only. An animal that's heterozygous for a mutant,
recessive gene looks wild type, but that gene can be passed on to
offspring.
Heterozygous - having two different alleles for a genetic trait.
Homozygous - having identical alleles for a genetic trait.
Wild Type - the way an animal looks with the greatest frequency in a wild
population ("normal").
The Genetics Wizard is the property of Barry C. Nielson
Copyright © 2000-2007 Barry C. Nielsen. All rights reserved.
These "terms of heredity" are provided to help people use the Advanced
Genetics Wizard.
Since there seems to be some confusion about codominance, I've provided
references
to published, scientific material to back up my use of the term.
Basic definitions of some common genetics terms are at the bottom of this
page.
Published References About Codominance
"In his law of dominance, Mendel did not accommodate different degrees of
dominance. As such examples were discovered (Bateson 1913), various
new terms were introduced. Within and between textbooks of genetics,
definitions are inconsistent. Various names have been used: partial
dominance, incomplete dominance, codominance, lack or absence of
dominance, intermediate dominance, imperfect dominance, egalitarian
dominance, and transdominance. The definitions vary from text to text and
depend on interpretation of allelic function, although an allele’s function is
seldom known and often must be assumed. In all these usages there is one
consistent aspect; each genotype has a distinguishable phenotype, and the
genotype may be inferred from the phenotype. Perhaps none of the terms
that have been used are all-inclusive, but some such term is desirable for
teaching purposes. We have chosen the term codominance as simplest,
shortest, and adequately inclusive. One can still use specialized sub-
definitions for well-analyzed cases. In our more that 20 years of teaching
this method has worked well."
BioScience Vol. 45 No. 2 Feb. 1995 pp. 98-104
Three neglected advances in classical genetics.
By Wilmer J. Miller and Willard F. Hollander
--------------------------------------------------------------------------------
"The definitions given or inferred for the intermediate form of dominance
usually require knowing the exact function of the gene. This is very seldom
known for most characters at present. All the "codominant" usages actually
show or imply 3 phenotypes for 2 codominant alleles for the monohybrid
genotypes in diploids. Why not use this consistency among names and their
usages as the single criterion and use only one name? I prefer the shortest,
codominance."
"So, for beginning students, as well as teachers and researchers, all genes
fit one of 3 categories: dominant, codominant, or recessive. When more
sophisticated nuances implying different functions are desired, then other
names can be used with a definition (please) for this next level of usage."
Brazilian Journal of Genetics
20, 4, 663-665 (1997)
By Wilmer J. Miller
Both of the quotes above were reprinted here with the permission of
Dr. Wilmer J. Miller, Professor of Genetics, Emeritus.
--------------------------------------------------------------------------------
Basic Genetics Definitions
Allele - either of the two paired genes affecting an inherited trait (one from
the father, one from the mother).
Codominant - an allele that causes the homozygous form to look different
than wild type and the heterozygous form to have traits of both. (All three
look different from each other.)
Dominant - an allele that causes the homozygous form and the
heterozygous form to look the same as each other, but different than wild
type.
Recessive - an allele that affects a animal's appearance if it's present in the
homozygous state only. An animal that's heterozygous for a mutant,
recessive gene looks wild type, but that gene can be passed on to
offspring.
Heterozygous - having two different alleles for a genetic trait.
Homozygous - having identical alleles for a genetic trait.
Wild Type - the way an animal looks with the greatest frequency in a wild
population ("normal").
The Genetics Wizard is the property of Barry C. Nielson
Copyright © 2000-2007 Barry C. Nielsen. All rights reserved.
Discover the mysteries of the natural world, unravel the fabric of time and
space or just figure out the odds of producing all those wild combinations of
genes without building a punnett square. The Punnett square is a diagram
designed by Reginald Punnett and used by biologists to determine the
probability of an offspring having a particular genotype. It is made by
comparing all the possible combinations of alleles from the mother with
those from the father.
space or just figure out the odds of producing all those wild combinations of
genes without building a punnett square. The Punnett square is a diagram
designed by Reginald Punnett and used by biologists to determine the
probability of an offspring having a particular genotype. It is made by
comparing all the possible combinations of alleles from the mother with
those from the father.
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