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By Enrique Patiño and Sergio Chaim,
with contributions from Tomoko, Ramona and others...
Last Update:
4/24/2005
Editor's note
This is work in progress, but if we wait until
we are done to publish it, it may be a while.
Plus, we think that we should try to get your
help in finishing this piece; particluarly the
gene tables. As editors, we decided to publish
this article as a draft. We will make an announcemet
on our forum each time we update or modify this
article. We will mark the new update date each
time. When we get close to where we are happy
with it, we may replace this article in the
April 2005 issue with a redirect page to the
revised gene tables. We will use pictures form different sources to fill in the tables where possible
Introduction
A lot of the material here we
have borrowed from other sources, including
some of the text. Some of the text has been
edited to fit our format, but some of it remains
a lot like the original source. But since what
we are doing here is simply organizing information
as a public service, we figure that any infringement
of copyrights may be forgiven. If anyone has
a problem or has comments about format or copyright
issues in essays like this, please send us an
email. We may be missing some citations. We
do not claim to be a scientific publication,
but do our best in referencing as well as we
can with our limited time. It is our hope that
this way of organizing information is useful
to our readers. Ata point where we are ready
to update this presentation, we may move it
out of this format into a separate e-booklet.
Guppy Genetics
- A Relative Old Science
One important point to make is that the study
of guppy genetics is not new. In the Natural
Environment Research Council’s Ecological Dynamics
and Genes (EDGE) Programme webpages (UK), someone
wrote: “In the early 1900s,
the guppy (Poecilia reticulata) was
already a subject of genetic investigation.
At this time, quantitative genetic theory and
methodology had not yet been developed, but
significant progress in the understanding of
guppy genetics was made without the knowledge
of polygenic inheritance and quantitative genetics.
The reason for this is that much variation in
male colour pattern is determined by a relatively
small number of genes which can be identified
by their distinct phenotypic effects. Moreover,
the sex-linked genetic control of these characters
and the ease of guppy rearing, facilitated these
early genetic experiments. After the introduction
of the concept of polygenic inheritance, guppies
were investigated using quantitative genetic
approaches, and various breeding designs which
included selection experiments, parent-offspring
regressions, sib analyses and combinations of
these techniques were employed.” In other
words, while some of the latest genetic techniques
such as genetic linkage mapping, microsatelites
and such modern laboratory techniques, as well
as important genetics studies in other teleosts
such ad the medaka and zebrafish, do shed important
light into "new frontiers" in guppy
genetics, we can't dismiss what we know about
guppy genetics from earlier work as useless
or irrelevant; especially at the level of the
sofisticated hobbyist. Fine tuning a strain
requires a lot of attention to the smallest
details.
Old Scientific Literature
While scientific papers published in the early
20th Century significantly contribute to our
undertanding of the genetic baseline of the
guppy, as a species, one has to know how to
interpret the information they offer. For example,
hobbyists know of the existance of phenotypes
that do not fall into the patterns describen
in Winge's papers, and that have not been discussed
in the scientific literature yet. How do these
phenotypes and corresponding genotypes relate
to Winge's genes? Or how do we know for sure
if Winge's "genes" are not really
"gene complexes"? This are important
questions because much of the genetics that
is important to the current hobbyist is linked
to the sex chromosomes.
Wild Guppies
Adapted from Brooks,
R. and J. A. Endler (2001)... Wild male
guppies are quite variable (within and among
population) with respect to secondary sexual
characteristics such as: body and tail size,
spots of pterin and carotenoid (red, orange,
and yellow), melanin (black and fuzzy black),
and structural color (iridescent blue, green,
and silver). It is comon for these color patterns
to vary in size, shape, and position among individual
males to such a degree that one could easily
identify individuals within a group. The genetic
basis for this variation has been well studied
(Endler 1983; Houde and Endler 1990; Endler
and Houde 1995).
Adapted from Lindholm and Breden (2002)...
Secondary sexual characters have been shown
to be attractive to females in the wild. A review
of the literature on the inheritance of these
attractive male traits reveals that color patterns,
caudal fin size and shape, courtship rates,
and a composite measure of attractiveness in
the wild are primarily sex linked in guppies.
An exception to this generalization is body
size. Male body size is an attractive traits
(to female guppies) and shows high heritability.
However, body size has not been shown to be
sex linked (Reynolds and Gross 1992; Yamanaka
et al. 1995; Brooks and Endler 2001).
Winge (1922a,b, 1927) and Yamamoto (1975) showed that
the presence of particular guppy color spots is controlled
by many genes exclusive to the Y chromosome, a couple
of genes exclusive to the X chromosome, several genes
that recombine between the X and Y chromosomes, and
a very small number on the autosomes. Of the color pattern
alleles that have been identified, at least 20 (but
up to 26) are on or very near to the non-recombining
section of the Y chromosome. Each male inherits and
transmits a subset of these alleles as a Y-linked
supergene (Yamamoto 1975).
At least seventeen alleles (up to 24) are known to
recombine between the X and the Y chromosome and five
are autosomal (Yamamoto 1975; Angus 1989). The autosomal
genes control body background color rather than the
presence of particular color spots (Yamamoto 1975),
except for the Zebrinus and Bar genes (Phang 2001).
Genes (for ornamentation) found on the X chromosome
or the autosomes are generally sex limited to males
in wild populations (Haskins et al. 1970). That means
that even if these are found on the X chromosome, their
phenotype is only expressed in males (in wild populations).
The exception seems to be those alleles related to melanin
production, which seem to be expressed in females as
well.
Lindholm and Breden (2002) stated.."The
extent to which color genes studied in domesticated
strains represent genes found in natural populations
is unknown." However, it has been determined
that the diverse color patterns of domesticated
color varieties of guppy are primarily determined
by X-linked and Y-linked genes (Phang et al.,
1985, 1989; Khoo et al., 1999a, 1999b, 1999c,
2003)." This means
that modern phenotypes may be inherited much
like in wild populations.
Modern Phenotypes In Today's Guppy
Labs
Many of the alleles responsible for some of
the modern phenotypes (modern strains) have
not been studied using the scientific method.
However, a lot is known, from empirical observations,
by breeders their "guppy laboratories" around
the planet. That is what we have as information
to determine the patterns of inheritance of
such modern phenotypes. This essay is just an
introductio to that subject. We basically need
your help.
If you are interested in engaging in serious
discussion about guppy genetics, or have information
you are willing to share with others, please
volunteer to moderate or help moderate a group
in guppylabs.info forum. Or, if you have specific
information that may be useful in editing, complementing,
or correcting the information presented here,
we would very much like to hear from you. Please
send any relevant information to: genetics_guppylabs.info
(replace the _ for @).
Sex Determination In guppies
Guppies have two different sex-determining chromosomes
(X and Y) and 22 homologous pairs of autosomal chromosomes,
for a total of 46 chromosomes (23 pairs). Recombination
(crossover) between the X and Y chromosome is suppressed
near a major sex-determining locus on the Y chromosome
(Angus 1989; Winge 1922a, 1927; Yamamoto 1975), but
there is an extensive homologous region in the Y chromosome
in which recombination between X and Y chromosome is
possible (about one half of the Y chromosome can pair
up with homologous regions of the X chromosome during
meiosis).
Khoo et al. (1999) suggest that the sex-determining
region is flanked on both sides by recombining regions
using a linkage map based on phenotypic traits. However,
Lindholm and Breden (2002) reported that the orientation
of the X and Y chromosomes during meiosis allows for
recombination in only two of 49 possible crossover sites
(4%), and suggested that recombination is not
very common in the pairing, homologous region of the
X and Y chromosomes.
Since YY males, which have no X chromosome, can be
fully viable, the X chromosome is assumed to
carry similar genes to the Y, except from those
in the sex determining region, (Winge and Ditlevsen
1938; Haskins et al. 1970; Angus 1989). Lindholm
and Breden (2002) suggest that the X chromosome
may have a region homologous to that of the
non-recombining region of the Y, but indicate
that so far no genes have been shown to be exclusively
linked to it. Traut and Winking (2001) suggested
that a large part of the non-pairing region
of the Y chromosome is made of "male-specific
repetitive DNA" [sequence], and that there
is structural variation among Y chromosomes
in this region - this is unlike any other chromosome,
where there are no "structural differences"-.
According to Nanda et al. (1994), This "male-specific
repetitive DNA" is particularly common
in domesticated strains. We will come back to
this later on our discussion.
Autosomal Effects on Sex
Determination
Some of the sex-determining factors in guppies are autosomal.
That is why it is possible to have XX males or XY females
(Nayudu 1979; Angus 1989). Colored (XX) females, one
of which (on the left of this picture) showed its anal
fin in the process of transformation to a gonopodium
(Winge, 1927)
(from
Winge, 1927)
Inheritance and Linkage
of Selected Traits In Guppies
Here we present informaton about color alleles
and traits that are known to be linked to the
sex chromosomes. We think that having this information
available to the hobbyist may be useful; you
decide. For now, consider this a "work
in progress."
Y-Linked Inheritance In Guppies
Large part of the non-homologous region of
the Y chromosome in guppies is made out of male-specific
repetitive DNA sequences (Traut and Winking
2001). It is also known that there is structural
variation among Y chromosomes in this same region
(Lindholm and Breden, 2002). This agrees with
results from other studies showing that Y chromosomes,
but not X chromosomes, of some domesticated
guppies carry large numbers of simple repetitive
DNA sequences (e.g., Nanda et al. 1990). Hornaday
et al. (1994) also showed that these male-specific
simple repetitive DNA sequences were not present
in recent descendants of wild guppies. According
to (reference),
this suggests some sort of control mechanism
limiting accumulation of such repeats through
natural selection in the wild. In our fishrooms,
our modern strains may have accumulated large
numbers of simple repetitive DNA sequences,
but are of no real consequence for "fitness"
since natural selection forces are not present
given our rearing protocols. However, these
male-specific repetitive DNA sequences may play
a role in "extending" the "normal"
coloration in male guppies of domesticated strains.
In addition to that information regarding eh
possible effects of sex-linked inheritance,
a large part of the genes responsible for guppy
coloration, body and tail
size are sex-linked in that they are
located in the sex chromosomes and are inherited
accordingly. Below is a table with a list of
Y-lined traits and genes.
X or Y-Linked Inheritance
(present in the X or Y chromosome - Crossing
over does occur between X and Y chromosomes
for these loci)
X-linked color patterns almost always have
male-limited expression. However, these can
be developed in females with testosterone treatment,
which can allow confirmation of inheritance
in females. Only patterns that have never been
reported from wild populations show weak expression
in females without testosterone treatment (Nigrocaudatus
I and II, Flavus, Pigmentiert caudalis, red
tail, blue tail, green tail, variegated tail,
and black caudal peduncle; references in table
below) and are most likely mutations restricted
to domesticated guppy populations.
By treating females with testosterone, Haskins
et al. (1961) showed that some color patterns
that were inherited on the X or the Y chromosome
in low-predation populations were exclusively
Y linked in high-predation populations. Thus,
the low-predation populations that are characterized
by higher levels of preference and elevated
levels of male coloration are also those that
exhibit color genes linked to the X chromosome
in the wild. So, X-linked inheritance is also
very imprtant for the construction of moders,
highly colored strains. We dont know how many
X-linked genes are extressed in females of moder
strains.
Autosomal Inheritance
The autosomes also have a few genes for pigmentation
and fin morphology. Zebrinus and Bar are similar
to the sex-linked pigmentation traits in that
expression is limited to males. The other known
autosomal genes for color ans shape are expressed
in both males and females.
Gene Table
This table was derived from: "will quote
source here soon"
Here is where one has to be careful aboout
how to interpret some of the phenotypes from
earlier publications.
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