Selectively Breeding Sheep

Transcription

1 Selectively Breedig Sheep ame Part 1: atural Selectio ad Selective Breedig What is atural selectio? What is selective breedig? What are the advatages of selective breedig? Give a example of selective breedig ad describe what trait might be selected for by the breeder. Part 2: Usig Puett Squares i Sheep Breedig Imagie you are a sheep farmer ad there is a strage disorder that is affectig the lambs that are bor i your flock. The paret sheep are healthy, but the lambs have bet limbs ad twisted spies. May of them are dyig, which will drastically reduce your icome to the farm ad the logevity of your flock. How ca you make wise matig decisios to prevet the births of these sick lambs? Spider Lamb Sydrome (SLS) i sheep is a recessive geetic disorder. It causes skeletal deformities icludig bet limbs ad twisted spies. It is difficult for sheep breeders to elimiate the risk of SLS i a flock because parets of SLS lambs do ot exhibit ay symptoms. This is a recessive disorder, so both parets must carry a recessive allele i order for the lamb to be affected. Breeders have the difficult task of usig a combiatio of selective breedig techiques ad DA tests to esure healthy lambs. DA tests ca be expesive, so istead of purchasig DA tests for a etire flock, breeders ca test certai sheep ad use Puett Squares to predict the probability of other sheep i the flock of carryig recessive alleles. 1

2 Selectively Breedig Sheep (cotiued) 1. You mate two sheep that are carriers for SLS, which meas both the ram ad the ewe have oe domiat allele ad oe recessive allele. Fill out the Puett Square. Possible Combiatios = Healthy Sheep =Healthy Sheep, but a carrier of the SLS gee = Lamb with SLS What is the probability that the offsprig will have SLS? What is the probability that the offsprig will be carriers? Do you thik that breeders should mate two SLS carriers? Why or why ot? 2. You mate a sheep that does ot carry a recessive spider allele with a carrier sheep. Fill out the Puett Square. 2

3 Selectively Breedig Sheep (cotiued) What is the probability that the offsprig will have SLS? What is the probability that the offsprig will be carriers? Do you thik that breeders should mate a RR sheep with a carrier? Why or why ot? 3. You buy a healthy ram from a eighborig farm, ad you do ot kow his geotype. You mate him with a SLS carrier ad the lamb is bor with SLS. Fill i the Puett Square with the geotype of the ram ad his offsprig. Ram 3

4 Selectively Breedig Sheep (cotiued) 4. A relatively simple geetic test is available for SLS. Accordig to the iformatio below, how much would it cost to test a aimal for SLS? If you have a large flock ad a limited budget, which sheep (rams or ewes) do you thik you should select for testig ad why? Costs associated with geetic tests available from Uiversity of Califoria- Davis Veteriary Geetics Laboratory. A gel electrophoresis showig DA bads for homozygous ormal (), heterozygous carriers (), ad homozygous SLS () sheep. 4

5 Selectively Breedig Sheep ame Part 1: atural Selectio ad Selective Breedig What is atural selectio? atural selectio is also kow as atural breedig. Aimals/plats have free choice i who to breed/reproduce with. What is selective breedig? Selective breedig is also kow as artificial selectio or uatural selectio. It is the process by which humas breed plats ad aimals for particular traits. What are the advatages of selective breedig? Breeders get to select which traits they wat i their livestock. Give a example of selective breedig ad describe what trait might be selected for by the breeder. Aswers will vary. A rabbit breeder chooses to breed the rabbits that have the best markigs. Part 2: Usig Puett Squares i Sheep Breedig Imagie you are a sheep farmer ad there is a strage disease that is affectig the lambs that are bor i your flock. The paret sheep are healthy, but the lambs have bet limbs ad twisted spies. May of them are dyig, which will drastically reduce your icome to the farm ad the logevity of your flock. How ca you make wise matig decisios to prevet the births of these sick lambs? Spider Lamb Sydrome (SLS) i sheep is a recessive geetic disorder. It causes skeletal deformities icludig bet limbs ad twisted spies. It is difficult for sheep breeders to elimiate the risk of SLS i a flock because parets of SLS lambs do ot exhibit ay symptoms. This is a recessive disorder, so both parets must carry a recessive allele i order for the lamb to be affected. Breeders have the difficult task of usig a combiatio of selective breedig techiques ad DA tests to esure healthy lambs. DA tests ca be expesive, so istead of purchasig DA test for a etire flock, breeders ca test certai sheep ad use Puett Squares to predict the probability of other sheep i the flock of carryig recessive alleles. 1

6 Selectively Breedig Sheep (cotiued) 1. You mate two sheep that are carriers for SLS, which meas both the ram ad the ewe have oe domiat allele ad oe recessive allele. Fill out the Puett Square. Possible Combiatios = Healthy Sheep =Healthy Sheep, but a carrier of the SLS gee = Lamb with SLS What is the probability that the offsprig will have SLS? There is a 25% chace the offsprig will have SLS. What is the probability that the offsprig will be carriers? There is a 50% chace the offsprig will carry the SLS allele. Do you thik that breeders should mate two SLS carriers? Why or why ot? Aswers will vary. 2. You mate a sheep that does ot carry a recessive spider allele with a carrier sheep. Fill out the Puett Square. 2

7 Selectively Breedig Sheep (cotiued) What is the probability that the offsprig will have SLS? There is a 0% chace the offsprig will have SLS. What is the probability that the offsprig will be carriers? There is a 50% chace the offsprig will be carriers. Do you thik that breeders should mate a RR sheep with a carrier? Why or why ot? Aswers will vary. 3. You buy a healthy ram from a eighborig farm, ad you do ot kow his geotype. You mate him with a SLS carrier ad the lamb is bor with SLS. Fill i the Puett Square with the geotype of the ram ad his offsprig. Ram 3

8 Selectively Breedig Sheep (cotiued) 4. A relatively simple geetic test is available for SLS. Accordig to the iformatio below, how much would it costs to test a aimal for SLS? If you have a large flock ad a limited budget, which sheep (rams or ewes) do you thik you should select for testig ad why? The cost of a test is $20. Testig rams should be tested because they will be mated with multiple ewes ad pass their gees off to more offsprig tha a sigle ewe. This is a more cost effective strategy. Costs associated with geetic tests available from Uiversity of Califoria- Davis Veteriary Geetics Laboratory. A gel electrophoresis showig DA bads for homozygous ormal (), heterozygous carriers (), ad homozygous SLS () sheep. 4