Bonus: Autosomal recessive polycystic kidney disease (ARPKD) is the lesser commo
ID: 212717 • Letter: B
Question
Bonus: Autosomal recessive polycystic kidney disease (ARPKD) is the lesser common of the two types of polycystic kidney disease, occurring in 1:20,000 live births, but it is also the most deadly. It is generally identified in the first few weeks after birth. Unfortunately, the kidneys are often underdeveloped resulting in a 30% death rate in newborns with the recessive version of the disease. 0 Suppose a man who is phenotypically normal, and whose mother was normal but his father had polycystic kidney disease, marries a woman who is also phenotypically normal. The parents of the woman are both normal. They are concerned that their children may inherit this disorder and decide to come to you, their genetic counselor. You sit down to explain to them that there may be cause for concern depending on their actual genotypes. Using one or more Punnett squares show ALL possible scenarios to this couple using the information you know about each of them and their parents. For each scenario provide the percent possibility or chance for a child to have the disorder, if any. Show your work. (2 pts)Explanation / Answer
Dominant and recessive are two terms used to describe the inheritence pattern of certain traits.
A dominant allele produces a dominant phenotype in individuals who have only one copy of the allele, which can come from only one parent.
For a recessive allele to produce a recessive phenotype, the individual must have two copies of that allele, one from each parent.
If an individual has one dominant and one recessive allele for a gene , he/she will have the dominant phenotype. But , they are considered " carriers " of the recessive allele [ the allele is present but cannot express itself in the phenotype]. It can be summed up as :
* dominant allele + dominant allele = dominant phenotype
* dominant allele + recessive allele = dominant phenotype
* recessive allele + recessive allele = recessive phenotype
* recessive allele + normal allele = carrier individual
In the above mentioned case, the information we have is ;
* The man having a diseased father and normal mother marries a normal woman whose parents are also normal.
The man has inherited only one set of chromosomes from his father , who obviously had two alleles for the disease. This means that the man might have inherited one recessive allele from his father. So, he might be a carrier but will not show the phenotype .
Or it might be that the man has not inherited the allele from his father due to the genetic recombination [ crossing over of chromosomes during meiosis] . In such a case he is not even a carrier of the allele.
The woman he marries is normal, neither a carrier nor affected by the disease, because her parents are normal.
When the two marry, there might be two scenarios of their children being affected by the disease--
Father is a carrier and mother is normal--
* Three sets of sperms will be produced after spermatogenesis -- both carriers, both are normal or one carrier and one normal.
The mother will produce normal ova after oogenesis.
After fertilisation , two scenarios can occur :
1] The sperm carrying the allele fertilises the ovum. The resulting zygote will have one recessive allele. The baby will be a carrier but will not show the phenotype.
2] A normal sperm fertilises the ovum. The resulting zygote will be normal i.e it will not carry any allele for the recessive disorder. So, the baby will be normal.
Therefore, the parents of the woman need not worry because any babies born to the couple will not be affected by the disease. They might carry the allele of the disease but will not be affected by it because two alleles are needed for the disease to express itself.
There will be 50% chance of carrier babies being born and 50% chance of normal babies . There will be 0% chance of babies born with the disease.