Our cairn terrier Comet (aka Geo-dog) is going to be the subject
of my second "geo-netics" cache series- merging genetics and
caching. Cairns come in many colors and Comet is a black brindle
color with tan points. Brindle means he has stripes and that a
single strand of hair has variation in color, in Comet's case that
variation is primarily tan.
A Punnett Square is a way to determine possible combinations of
alleles (or traits) and expected ratios of these traits from two
parents. Each parent contributes one allele for a single trait to
the offspring, so there are two sets of two alleles (one set from
each parent) that can be expressed in offspring. As an example lets
use eye color. The father has brown eyes so he could be BB or Bb
because the allele for brown (B) is dominant over the allele for
blue (b), which means you only need one B for brown eyes. We will
say he is Bb. The mother has blue eyes so she has to be bb because
for a recessive gene to be expressed there need to be two copies. A
Punnett Square on eye color would be Bb x bb. (see image) 50% of
offspring (or 2) would have brown eyes (Bb) and 50% (o r2) would
have blue eyes (bb).
Cairn terriers can be cream, sand, grey, red or brindle colored.
A brindle coat requires complex genetics. Brindle is one of the
recessive genes on the K locus. There are three K locus genes - K
(dominant black), kbr (brindle) and k (non-solid black - allows A
locus to be expressed). K is the top dominant and k is the bottom
recessive. kbr sits between the two. A brindle coat is entirely
dominated by K (so just one K gene will stop brindle from being
expressed). A brindle dog can be kbrkbr or kbrk. A dog with one or
two kbr genes or two kk genes will express whichever gene it has on
the A locus. The following list shows how the different A locus
genes affect the appearance of brindle.
Brindle + AyAy (sable),Dominant, dog will be solid brindle
Brindle + atat (tan points) - dog will be black with brindle
points = COMET
To find the cache you have to answer some questions about Comet
and his 15 litter mates. A no brindle male mates with a solid
brindle female. Kkbratat x kbrkbrAyat.
The cache is at N39 04.ABC, W104 54.DEF
AB: Two digits. What is the percentage of non-brindle offspring?
Now subtract 3.
C: How many non-brindle offspring are there?
DE: What is the percentage of solid brindle offspring? Now add
1.
F: Including Comet, how many offspring are brindle with tan
points? Now subtract 3.
You can check your answers for this puzzle on
Geochecker.com.