Download STEP 1 - BrainMass

STEP 1
The first thing you need to do is determine the genotype of the captive minks. It
says that he wants to “maintain production of all long-haired minks”. This suggests to
me that in his current mink population every offspring is long-haired. Now let’s think
about the genotype/phenotype relationship. We know from the statement that long hair
(L) is dominant over short hair (l); this means that to have a long-hair phenotype (a
long haired animal) we only need one dominant gene (L). Therefore minks with genes
LL and Ll will be longhaired and ll will be shorthaired. Mating LL with LL will give
us only LL offspring, ll x ll will give only ll animals, whereas LL x ll, LL x Ll, and Li x
ll will give us a mix of short and long haired offspring (LL, Ll or ll). The predicted
ratio of each of these combinations can be figured out using the punnet square
technique, and will be important to us when we determine which wild minks to keep in
captivity. So knowing all that, and knowing that in captivity we only get longhaired offspring 100% of the time, what genotype (ll, Ll, or LL) are the captive
animals?
STEP 2
The statement tells us we have 5 wild minks, 4 with long hair and 1 with short
hair. We must now figure out the genotypes of these wild minks using their phenotypes
and/or punnet squares. To maintain 100% long-haired mink production in captivity
we want to select the two minks with what genotype? (Think back to step 1 for
help). Let start with the one short-haired mink, remember short hair is a recessive trait,
therefore and animal must have two copies of the short hair allele to express short hair
as a phenotype. Therefore the short hair mink has to have what genotype (LL, Ll
or ll)? Will a mink with this genotype produce all long haired offspring when
mated with our captive animals?
To determine the genotype of the 4 minks with long-hair will must conduct
mating studies. We can mate these 4 minks with either the short haired wild mink with
known genotype or the captive minks with known genotype (step 1) and see what hair
lengths the offspring have. We will use a punnet square to predict what the offspring
should look like when different genotypes are mated together, then we would (if we
were the breeder) actually mate the animals and see what the offspring look like). We
could then compare actual to predicted and determine the wild minks genotypes. We
are looking for two wild mink that will only produce long haired mink when mated
with our captive animals. Perform a punnet square with the following combinations
LL x LL, LL x Ll, Ll x Ll, these represent all the possible combinations when
mating longhaired animals together, you could also try LL x ll, and Ll x ll, to
determine the offspring genotypes for long haired animals (either LL or Ll) mated
with a short haired animal. The combination of you captive genotype with either LL
or Ll (the possible wild long haired genotypes) that gives 100% long-haired animals
(i.e. no ll genotypes) are the animals we are looking for.
EXAMPLE
A punnet square example using the smooth (S) and wrinkled (s) pea, where the
smooth allele is dominant. We want to mate a smooth pea, genotype Ss with a
wrinkled pea, genotype ss. We place the parent genotypes on the outside and combine
the rows with columns to get the possible offspring (see below). What we find is that
we predict 50% of the offspring to be smooth (Ss) and 50% to be wrinkled (ss) or a 1:1
ratio. In actuality we may not get this ratio if we mated these parents once because
these are predictions based on the likelihood of certain alleles being available in the
female egg and male sperm (remember a male with genotype Ss will have 50% of his
sperm with s and 50% with S after meiosis, same for a female). Therefore when we are
conducting mating studies to determine what the genotype of an animal with known
phenotype is we want to do each mating or cross multiple times and look at the
phenotypic ratio (i.e 1:1) of all of the offspring to determine the genotype of the
parent(s).
S
S
S
Ss
Ss
S
Ss
Ss
See this website or search punnet square if you need more help with punnet
squares. http://www.borg.com/~lubehawk/psquare.htm
Step 3
Bringing it all together/review. You need to do the following:
1. Determine the genotype of the captive animals based on the information in the
statement and the information I discussed in step 1.
2. You want to determine the genotype of the wild animals by using their
phenotype of punnet squares (mating studies).
3. You would advise the breeder to conduct mating studies (remember multiple
matings of each pair), look at the ratios of the phenotypes of the offspring i.e 1
short hair: 1 long hair and determine the genotype of the wild minks by
comparing your predicted ratios from the punnet squares to the actual offspring.
4. Then the breeder should select animals that just give long haired offspring when
mated with his captive animals. If this doesn’t occur he shouldn’t keep any of
the wild minks, unless he is ok with some short haired offspring.
Good Luck