Polysaccharide storage myopathy (PSSM) is a dominant aurosomal hereditary condit
ID: 209270 • Letter: P
Question
Polysaccharide storage myopathy (PSSM) is a dominant aurosomal hereditary condition in horses chat can cause muscle damage and inability to move. It is often referred to as "tying-up" Equine hyperkalemic periodic paralysis (HYPP) is also a dominant autosomal hereditary condition in horses that has been traced back to a horse named Impressive who died in 1995 at the age of 26. Symptoms of HYPP include muscle twitching and unpredictable paralysis attacks that can lead to sudden death. Recall that with dominant disorders, only one dominant allele will result in the condition being manifested. A stallion with HYPP and PSSM whose mother had neither disorder is crossed with a mare who has neither HYPP nor PSSM. 6. . Construct a Punnett square and state the probability that this cross will result in a foal that hats neither HYPP nor PSSM. What are the possible genotypes and phenotypes of all the foals? Probability of a foal without HYPP or PSSM: . . Possible genotypes and phenosypes of all of the foals:Explanation / Answer
Both PSSM (Polysaccharide Storage Myopathy) and HYPP (Hyperkalemic Periodic Paralysis) are autosomal dominant disorders. The allele for PSSM can be denoted by the letter 'M' and that for HYPP by the letter 'H'.
MM - PSSM HH - HYPP
Mm - PSSM Hh - HYPP
mm - Normal hh - Normal
Since the cross here contains two different traits, it is considered as dihybrid cross.
1) A Mare is an adult female horse, Stallion represents adult male and foal is an offspring.
Here, the cross is made between a stallion who has both PSSM and HYPP. Hence its genotype can be either MMHH or MmHh. Since it is already said that the mother of this stallion is a normal female, it is sure that the stallion might have got normal alleles for both PSSM and HYPP from his mother ( he might have inherited the disease allele from father). Hence the genotype of stallion must be MmHh (ie, heterozygous for both the diseases). The mare is normal for both the traits and hence its genotype will be mmhh.
The cross can be represented in a punnet square as follows :
MmHh X mmhh
The probability of a foal that has either PSSM nor HYPP (ie, with genotype 'mmhh') is 1/4 or 0.25.
2) Four types of foals are possible for this cross. Their genotypes and phenotypes are respectively,
3) Probability of foal without PSSM or HYPP ( ie, with genotype mmHh or Mmhh) is 2/4 ie 0.5
MH Mh mH mh mh MmHh - Both PSSM & HYPP Mmhh - Has PSSM and no HYPP mmHh - Has HYPP but no PSM mmhh- Normal ( no PSSM & HYPP)