Question

Lois Lane Kent's husband has passed on three unusual traits to their daughter; X-ray vision, sensitivity to kryptonite and muscles of steel. A book given to Mr. Kent by his mother states that the genes for these traits are dominant, and that the vision and muscle loci are located 16 map units apart on the same autosome, while the kryptonite locus is located on another autosome.  

Assuming that an average human male eill someday marry this "Super Girl", Lois is worried about the chances that her grandchildren will inherit the same genes that have made her daughter such a difficult child to raise. What is the possibility of Lois Lane Kent's grandchildren will have:

A) All three dominant traits

B) X-ray vision and sensitivity to kryptonite, but normal muscles?

Answer 1

LLK's daughter has one chromosome with the dominant X-ray and Muscle allele linked 16 map units apart (inherited from Superman). On the other homologous chromosome she has the normal vision and muscle allele linked 16 map units apart (inherited from Lois Lane). On a different chromosome she has the kryptonite sensitive allele (from Superman) and the other homologous chromosome has the kryptonite resistant allele (from Lois Lane). Her average human male husband is homozygous recessive for all traits. When LLK's daughter makes eggs through meiosis, there is a 16% chance of recombination between the allele for vision and the muscles. Therefore,
42% of her eggs will carry a chromosome with the X-ray vision allele and the muscle of steel allele.
42% of her eggs will carry a chromosome with the normal vision allele and the normal muscle allele.
8% of her eggs will carry a chromosome with the X-ray vision allele and the normal muscle allele.
8% of her eggs will carry a chromosome with the normal vision allele and the muscle of steel allele.

50% of her eggs will carry another chromosome with the kryptonite sensitive allele.
50% of her eggs will carry another chromosome with the kryptonite resistant allele.

For LLK's average male husband:
100% of his sperm will have a chromosome with the normal vision allele and the normal muscle allele, and a chromosome with the kryptonite resistant allele.

Combining the LLK's daughter's eggs randomly with her average male husband sperm, we get:

A) Answer is 21%, because 42% of her eggs will have a chromosome with the X-ray vision allele and the muscle of steel allele, and 50% of those will also have a chromosome with the kryptonite sensitive allele. It doesn't matter what sperm her husband donate (they are all the same with regards to these 3 alleles) since his alleles are all recessive.

B) Answer is 4%, because 8% of her eggs will have a chromosome with the X-ray vision allele and the normal muscle allele, 50% of those will also have a chromosome with the kryptonite sensitive allele.