Name: __________________________________
Date: ___________________________________
Flynt - ____th Grade Science
Mr. Flynt and I have a cat named Rainy. She is solid grey with a tiny white locket on her chest. At first
glance, she seems to have a very simple coat pattern, right? Not so fast! Her genotype is as follows: BB dd
XoXo aa TT ww C- Ss (or ss).
Got all that? The color and marking pattern of a cat's coat is determined by polygenic inheritance of no
fewer than eight (8) different genes, much like human eye color, which is believed to be controlled by 6 or more
genes. For each individual gene, there may be a variety of inheritance patterns, including but not limited to
multiple alleles, incomplete dominance, codominance, sex-linked inheritance, epistasis, and pleiotropy—just to
name a few.
Are you ready to explore all of these genes and inheritance patterns in order to wrap your head around
all the different possibilities that arise when polygenic traits—some with multiple alleles—are involved in
determining a phenotype?

The Color Gene: Rainy is most likely BB.
o
The black allele, "B", is dominant over the other two alleles, b (chocolate) and bl (cinnamon).

The genotypes BB, Bb, and Bbl all produce either a solid black coat or a black-and-brown tabby
(striped) coat, depending upon the presence of the agouti gene (mentioned later).


o
Thus, the genotypes bb and bbl both result in dark brown coat color called “chocolate.”
The light-brown cinnamon allele, "bl", is also a rare allele and is recessive to both black (B) and chocolate
(b).


Even though Rainy looks gray, she is technically a black cat. Her black color is diluted to gray
(actually called blue) by another gene. She is most likely BB based on her parentage and the
rarity of the other two color gene alleles.
The dark-brown chocolate allele, "b", is a rare allele and is recessive to black (B) but dominant to
cinnamon (bl).

o
Technically, the black is an almost-black, super-dark brown that is virtually black. There
is not such color as true back in cats.
The genotype blbl results in a light brown coat color called “cinnamon.”
The Color Density Gene: Rainy is dd.
o
This gene controls the uniformity of distribution of pigment throughout the hair and comes in two alleles:
dense, "D", and dilute, "d".

The dense allele, "D", is dominant and causes pigment to be distributed evenly throughout each
hair, making the color deep and pure. A dense coat will be black, dark brown, medium brown, or
orange.

The dilute allele, "d", is recessive, and results in pigmented regions in the hair shaft surrounded
by translucent un-pigmented areas, allowing white light to shine through and diluting the color.

A black coat dilutes to “blue.”  This is why Rainy is gray.

A chocolate coat dilutes to “lilac.”

A cinnamon coat dilutes to “fawn.”

An orange coat dilutes to “cream.”

The Agouti Gene: Rainy is aa.
o
This gene will control ticking and comes in two alleles: agouti, "A", and non-agouti, "a".
o
The agouti allele, "A", is dominant, and produces a banded or ticked (agouti) hair, which in turn will
produce a tabby (striped or spotted) coat pattern.
o
The non-agouti allele, "a", is recessive. It suppresses ticking, which in turn will produce a solid-color coat
(like Rainy’s). This gene only operates upon the color gene (black, dark brown, or light brown).
o
The non-agouti allele (a) is masked by the dominant “O” orange allele of the orange-making gene, which
is why all orange cats are striped tabbies.


Thus, there are NO solid orange cats!
The Tabby Gene: Rainy is probably TT.
o
This gene is only expressed in cats that are AA or Aa for the agouti gene. This gene determines the way
the agouti gene is expressed.

Since Rainy is homozygous recessive for the agouti allele (aa), we can’t see her “stripes” to know
for sure which genotype she carries. However, TT is most likely her genotype based on her
parentage and the most common alleles in the US.

o
The TT genotype results in the common striped and spotted patterns (both are known as mackerel) that
are very common the US domestic cats.

o
o

The mackerel allele (T) is codominant to Ta and dominant over tb.
The TaTa genotype results in an all-over agouti ticked coat known as Abyssinian (very rare).

o
Even cats with solid coats sometimes show very faint stripes on their tail or legs. This is
true of Rainy. These ghost stripes, along with the phenotype of her mother, Annie (who is
TT for her mackerel stripes), plus the rarity of the other two alleles in US domestic cat
populations, leads me to conclude that Rainy is most likely TT.
The ticked or Abyssinian allele (Ta) is codominant to T and dominant over tb
The TTa genotype is the heterozygous combo of the mackerel and Abyssinian alleles.

These two alleles are probably co-dominant or incompletely dominant with respect to one
another.

This extremely rare genotype is mainly the result of careful selective breeding and results in a
golden chinchilla coat pattern (incredibly rare).
The tbtb genotype results in the “classic” bulls-eye tabby swirl pattern that is common in British domestic
cats.

The dominant mackerel allele (T) is rare in Britain. The recessive tb allele is not as common in the
US, and thus classic tabbies are rare here.

The classic bulls-eye tabby allele (tb) is recessive to both T and Ta.
The Epistatic Orange Marking Gene: Rainy is oo.
o
The orange allele, "O", is epistatic , which means that it converts all black or brown colors (BB, Bb, Bbl,
bb, bbl, blbl) to orange.
o
The orange allele, "O", also influences coat pattern, as it blocks the homozygous recessive agouti
genotype (aa) that results in solid coat colors (more on this later).

o
Thus, all orange cats are tabbies. There are NO solid orange cats.
The recessive non-orange allele, “o”, allows full (normal) expression of the black or brown colors,
whether solid or striped.

Rainy is gray, not orange, so she (and every other non-orange cat) must be homozygous recessive
for the orange marking gene.
o
This orange marking gene is sex-linked -- it is carried on the "X" chromosome beyond the limit of the "Y"
chromosome. (Are we having fun yet?)




If a male possesses the recessive “o” allele (XoY genotype), all colors except orange
(black, dark brown, or light brown) will be expressed as they normally would (they can
be solid or striped).

If a male possesses the dominant “O” orange allele ( XOY genotype), all colors
determined by the color gene will be converted to orange (and he will be an orange
tabby).
o
In females (XX), one orange marking allele (either O or o) is carried on each of the two "X"
chromosomes. Thus the possible genotypes are XOXO, XOXo, or XoXo.
o
Even though everyone uses a capital and lower case letters for the orange marking allele and talks about
this gene using dominant/recessive terms, the exact type of inheritance pattern between the two orange
marking alleles is still not fully understood. For our purposes, it basically seems to work a lot like
codominance.

If the female is homozygous recessive for non-orange, "oo", all colors except orange (black, dark
brown, or light brown) will be expressed (either solid or striped, but no orange).

If she is homozygous dominant for orange, "OO", all colors will be converted to orange (and she
will be an orange tabby).

It she is heterozygous for orange, "Oo", then the female with either be black-and-orange (known
as tortoiseshell) or black/orange/white (known as calico), depending on white spotting gene,
another gene we will mention later.
The Albinism (Oriental) Gene: Rainy is C- (most likely CC).
o
This gene controls the amount and distribution of body color. It comes in five (yes, five) alleles: full color
(C), Burmese (cb), Siamese (cs), blue- eyed albino (ca), and albino (c).
o
Neither Rainy nor her parents or sibling show any signs of being anything other than CC or C-, so I’m not
even going to get into all the different genotypes and phenotypes associated with this one gene. However,
if you are interested in the coat colors/patterns of Siamese, Burmese, Tonkinese, blue-eyed albino, or true
albino cats, you can read more here: http://www.netpets.org/cats/reference/genetics/catgenetics4.html
The Epistatic White Gene: Rainy is ww.
o
The dominant white allele, "W", converts ALL other colors (striped, solid, black, brown, orange, etc) to
solid white.

o
o
Solid white cats can thus be either WW or Ww for the white gene.
The recessive non-white allele, “w”, allows full (normal) expression of the orange, black or brown colors,
whether solid or striped.


In males (XY), there is no homologous pairing since they only have one X chromosome and thus
only one allele for the orange marking gene. As a result there is no true dominance/recessive
blocking effect in males: they are either orange (if they have the “O” allele on their single Xchromosome) or non-orange (the recessive “o” allele is on the X chromosome).
Rainy is gray, not solid white, so she (and every other non-solid-white cat) must be homozygous
recessive (ww) for the epistatic white gene.
The epistatic white gene is associated with developmental defects that can result blue eyes and
degenerative changes in the succule and cochlea of the ear, resulting in partial or total deafness in many
all –white, blue-eyed cats.
The Piebald or White Spotting Gene: Rainy is either Ss or ss.
o
The white spotting gene results in coats that include both white markings along with solid or patterned
patches. The white spotting gene exhibit variable expression, ranging from coat patterns that are almost
entirely white with only small patches of color to coats that are almost entirely non-white (either solid or
patterned) with only a small patch of white hair on the throat or belly.

o
o
This variable expression indicates that either there are other genes that affect/influence the
amount and location of the white spotting, or that there are multiple alleles and/or multiple genes
that are involved (or all of the above).
The SS genotype is believed to result phenotypes that are mainly white with just a little bit of color.

Cats with “Van” patterns are almost all white with only a little color around the ears and tail.

Cats with “harlequin” patterns are mainly white with a few large and/or small patches of color
distributed randomly.
The Ss genotype is believed to be responsible for a variety of bicolor coat patterns, including mask and
mantle, hat and saddle, and tuxedo patterns, as well as smaller white patches or blazes on the face, throat,
chest, and/or stomach of an otherwise non-white colored cat.

In general, the white patches associated with the Ss genotype start as an inverted (upside-down)
white "V" that starts in the center of the forehead, nose, or chin and passes down the face and
under the chin, down the chest and belly, down to the legs and feet, which are usually also white.

Ss genotype is believed to be associated with cats for which approximately half or more of their
coat is non-white.

This may include cats like Rainy that have only a few white hairs limited to a small
“locket” in the throat region.
o
The ss genotype produces a normal coat without any white spots (can be either
solid or striped).
o
Recent genetic research suggests that there may be several types of minor white
markings (including gloves, mittens, lockets, and brisket spots) that are
determined independently by genes other than the white-spotted gene.

A separate gene for white “gloving” has been recently confirmed as
being responsible for the white paws seen in Birman cats.


Most breeders and geneticists now believe that there are probably similar independent genes, as
yet unidentified, that control other varieties of minor white spotting—including lockets, brisket
spots, and mittens—in the same way that gloves are determined in Birmans.

o
In this case, a Birman would be “ss” for white spotting and “gg”
for gloving (all Birmans are homozygous recessive for the
gloving trait).
In this case, cats like Rainy (as well as her dad) would probably be homozygous recessive
for the white spotting gene (ss), since their white lockets would be determined by another
gene with an entirely separate set of alleles.
Unlike the white gene or the albinism gene, the white-spotting gene does not affect eye color: if your all
white cat has green eyes, it is most definitely a colored cat with one big white spot all over.
Explain whether using a single pedigree chart would work to trace inheritance patterns of polygenic traits like
human eye color and cat coat color that are determined by multiple genes, each with multiple alleles and
inheritance patterns.
Think about and describe an example of a single phenotype that is determined by genes (genotype) but can be modified
later depending on environmental factors and/or an individual's life choices. Are these changes to phenotype heritable?
Why/why not?
Are genetic disorders always inherited from one or more of an offspring’s parents? Why or why not? If yes, explain why
some people get genetic diseases even though there is NO family history of that genetic disease. If not, explain why some
genetic disorders are inherited while others are not (if that’s the case), OR explain why NO genetic disorders are passed
on via heredity. If an individual DOESN’T inherit a genetic disease from one or more parents, are these NEW genetic
diseases able to be passed on to the NEXT generation in every case? Make sure you can defend explain your view on all
of these points.
How would you determine if wrinkled leaves or smooth leaves is the dominant factor if you start with true-breeding plants
for each trait? What exactly would you do to investigate this question? What observations/data would you look for to tell
you which trait is the dominant one?