Question

The last sections of #6 should read: Anurak remembers hearing that one of his parents' grandmothers had the same disease, but he can't remember which parent. Do you think it was his mother's grandmother or his father's grandmother? (1points) Is it surprising that his great-grandmother had the disease, given that she is a female? Why? (2points) Thanks Scott

Answer 1

Part A: Being a genetic counsellor I would tell them not to worry about their child having the disease, because their child will be born normal, without any disease. This is due to the imprinted gene which is maternally-expressed. Maternally-expressed imprinted gene means an allele in Anurak's gene which he inherited from his mother is causing the disease to express. Whereas the disease is said to be paternally-silenced that means even though Anurak has the disease but his wife is normal, and the disease cannot be passed from father to offspring (paternally-silenced).

During gamete formation, one allele from each parent comes and forms a new genotype (gene), [Mendalian inheritance], in this case, the mutation in imprinted gene causing the disease, which is said to be maternally-expressed is passed on to Anurak from his mother, and even though his father had the same disease theory says that he would not have passed.

Part B: When Anurak's mother wants to have a child with a different person (not Anurak's father), being a genetic counsellor I would tell them to worry that their child may be born with the disease (50% chance). Because Anurak got this disease from his mother, so his mother is also affected with the disease there is a 50% chance out of the 4 possible offsprings that the child will also get the disease.

When the gamete formation happens, one allele from each parent will interact and make a genotype, so out of 4 alleles, 1 allele is from Anurak's mother, which will pass on to the 2 offspring (if considering 4 offsprings in each case of gene formation) and other 2 might be a carrier or normal depending upon the genotype makeup.

Part C: I surely believe that it was Anuraks's, mother's grandmother had this disease as the disease is maternally expressed, and paternally silent. Anurak's mother's grandmother passed the diseased allele to Anuraks's grandmother and from there it was passed to Anurak's mother, now here Anurak's mother's phenotype is not discussed, she definitely has the disease because theory says, half of the progeny of the affected females will be affected.

Part D: No, it is not surprising that his great-grandmother had the disease, given that she is a female. As the disease is said to be maternally-expressed, only mothers having the disease can pass it on to 50% of the progeny, and paternally it is silent.

Pedigree Chart:

Maternal Great-grandfather Maternal Great-grandmother Grandmother Anurak's Mother New Man Anurak's Father Anurak Half progeny have disease irrespective of gender Carrier (irrespective of gender) Normal progenies But none are infected