A geneticist determines that long hair length in mink is dominant over short hair (recessive). his friend breeds mink in captivity with long hair esp for the fur inducstry and has received permission from the Kansas Department of Wildlife and Parks to trap 5 wild mink to add to his breeding stock to reduce effects of inbreeding within his colony, but he wants to otherwise maintain production of all long-haired mink. 4 of the 5 wild mink have long hair, the 5th has short hair. If he has room to house only 2 more mink as breeding stock during the subsequent 5-year period, explain how his geneticist friend should advise him to procced in conducting a test cross to detemine which (if any) of the wild-trapped mink he should retain for his breeding project for the next 5 years. (I am assuming mink breed year round and prodcue 5 litters per year)© BrainMass Inc. brainmass.com September 28, 2022, 2:15 am ad1c9bdddf
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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 long-haired offspring 100% of the time, what genotype (ll, Ll, or LL) are the captive animals?
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.
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 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
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.
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