Question

In zebrafish, the half baked (hab) gene is caused by a mutation in E-cadherin. A new allele of this gene, k51, has a wild-type phenotype as a heterozygote, and a strong lethal phenotype as a homozygote. However, k51/deletion has a slightly more dramatic phenotype than k51/k51. This test tells us that the new allele is: O a null allele O codominant. O dominant lethal. O temperature sensitive. O haploinsufficient. O a leaky allele O incompletely dominant. O dominant negative. O a recessive lethal allele.

Answer 1

In the first case E-cadherin is affected by the new gene. The genes that govern this protein are mostly tumor supressor genes. But here we see,

The new allele has a lethal phenotype in its recessive condition and wild type in its heterozygote condition. But in case of a deletion the allele shows a worse scenario than lethality. Such a condition can be defined by a recessive lethal allele. This can be compared with that of sickle cell anaemia but in this case heterozygote has a different phenotype than wild type phenotype.

In the second case, the new gene has lethal homozygote at 28 degree celsius and no phenotype at 22 degree celcius so the gene is temperature sensitive. This is a conditional mutation that produces mutant phenotype at 28 degrees and null phenotype at 22 degrees.