Genetics is a branch of biology that studies
heredity and how certain characteristics or traits
are passed from parents to offspring.
Genetics means the study of inherited variation also known
(1)The study of genes through their variation.
(2) The study of inheritance. Polymorphism is the
occurrence, together in the same population, of more
than one allele or genetic marker at the same locus with
the least frequent allele or marker occurring more
frequently than can be accounted for by mutation alone.
Genes are the fundamental physical and functional unit
of heredity, which carries information from one
generation to the next.
We begin with explaining the chromosome. The structure of
the chromosome consists of two long strands of
Deoxyribonucleic Acid (DNA) that are bound together, and
twisted into the shape of a helix. The DNA helix is
organized additionally by becoming wrapped around proteins
called histones forming a DNA-protein complex known as a
nucleosome. During cell division, the nucleosomes coil
further into a dense, visible (stainable) mass of DNA most
people think of as a chromosome.
Homologous chromosomes are a matching pair of chromosomes
containing the same genetic loci in the same order. One of
the homologous chromosomes is received from the father, and
the other is received from the mother.
Because there are two chromosomes in the pair, the pair
contains two different alleles at every loci, one on each
chromosome. This allows for a great deal of variation in
individuals, by means of dominant traits, recessive traits,
polygenic traits, and masking genes. In the figure to the
right, we show a set of chromosomes showing only one locus.
However, a chromosome pair can have more than one locus as
you will learn with angelfish genetics (see next figure).
Locus is a single
set of alleles on the chromosome.
Ex: D/+ (Black Lace) shows only
one position (location) on the chromosome.
Loci is more than one set of alleles on the chromosome.
Ex: D/+ - S/+ (Black Ghost ), this
shows two positions (locations) on chromosome.
Understanding the basics of the chromosome will help us
when learning the genetics of angelfish, the alleles, and
Below are a few common terms to help you understand other
sections in the genetics category of this site. For a full glossary of terms used
in genetics, please see our "Genetic
Allele: One alternative of a pair or group of genes
that could occupy a specific position on a
Chromosome: A linear strand of DNA harboring many
Dominant: An allele producing the same phenotypic
effect whether inherited heterozygously or
homozygously; an allele that "masks" a recessive
Gene: A unit of genetic information that occupies a
specific position on a chromosome and comes in
multiple versions called alleles.
Genotype: The genetic constitution of an organism.
Heterozygous: Having a genotype with two different
and distinct alleles for the same trait.
Homozygous: Having a genotype with two of the same
alleles for a trait.
Phenotype: The physical or observable
characteristics of an organism.
Recessive: An allele producing no phenotypic effect
when inherited heterozygously and only affecting the
phenotype when inherited homozygously; an allele
"masked" by a dominant allele.
It is important to remember that an Angelfish's color,
growth rate and adult size are a product of not only it's
genetic material but also environmental factors. These
factors include, but are not limited to, tank size,
temperature, frequency of feeding, nutrition, water quality,
and the length of day called the "photo period."
Norton has spent over 20 years studying the genetics of
Angelfish. Her articles will help you to understand how the
genetics and environmental influences work together to
produce many of our angelfish varieties. The
terminology" will allow you to have a better understanding of
the term itself and how it works.