Genetics Background info: About 30% of the Irish population has red hair and an inability to tan (MC1R). This is due to an unusual variant of the pigment molecule melanin, called red melanin. Another fairly common inherited condition is restless legs syndrome (RLS). It is characterized by an irresistible urge to move ones legs and can interfere with sleep, leading to chronic sleep deprivation. Both red melanin and restless leg syndrome are recessive, and their genes are on different chromosomes. Molly and Sean met in San Francisco and were drawn to each other because of their striking red hair and very pale skin (both had parents who emigrated from Ireland). Neither has a family history of restless leg syndrome. A few years later they married and had identical twins, Jerry and Garcia, both are red heads and their legs are fine. Danny and Betty lived in San Francisco too. They both had brown hair, and Danny suffers from restless leg syndrome. Their daughter, Cali, has dark brown hair and her legs are fine. Jerry and Cali have a son, Henry. He has red hair, does not tan and has restless leg syndrome. Complete the family tree by assigning the genotypes based on the phenotypes described above (Hint: obviously you can get some information from the phenotype of the individual. Further clues can be obtained from the phenotypes of the progeny). Use R or r for restless leg syndrome alleles or an underscore if the allele could be either R or r. For example, R_ would represent either Rr or RR. Use M or m for the red melanin alleles, M_ would represent MM or Mm. A) (1.5 point) Which individuals must be heterozygous for restless leg syndrome? B) (1.5 point) Which individuals might be heterozygous for restless leg syndrome? C) (1 point) Which individuals must be heterozygous for the red melanin gene? D) (2 point) Garcia marries a woman who has restless leg syndrome and red hair, what is the probability that a child of theirs will inherit both traits? Show your logic using probability, or draw a Punnett square to show the potential genotypes of their progeny. M S D B C H Solution A) Cali, Jerry; Since Henry has restless leg syndrome (rr), both of his parents should carry atleast one copy of r allele. So, Jerry and Cali are heterozygous for the restless leg syndrome. B) Molly and Sean; Since Both Molly and Sean have fine legs but their son is heterozygous for the syndrome, either of them is also heterozygous for the restless leg syndrome. C) Since Henry has red hair and no tan tendency (homozygous for red melanin gene), both of his parents should have one copy of red melanin gene. Jerry has red hair (mm) but Cali has dark brown hair, so, Cali is heterozygous for the red melanin gene. D) Genotype of woman to whom he is married = mmrr promability of getting mm = mm (the woman) x mm (garcia)= 1 Probabiity of getting rr= Rr x rr = 1/4 Probability of Garcia to be Rr is 1/2. Total probability of rr = 1/4 + 1/2= 3/4 Total probability of rrmm= 3/4 x 1= 3/4.

1. Genetics
Background info: About 30% of the Irish population has red hair and an inability to tan (MC1R).
This is due to an unusual variant of the pigment molecule melanin, called red melanin. Another
fairly common inherited condition is restless legs syndrome (RLS). It is characterized by an
irresistible urge to move ones legs and can interfere with sleep, leading to chronic sleep
deprivation. Both red melanin and restless leg syndrome are recessive, and their genes are on
different chromosomes.
Molly and Sean met in San Francisco and were drawn to each other because of their striking red
hair and very pale skin (both had parents who emigrated from Ireland). Neither has a family
history of restless leg syndrome. A few years later they married and had identical twins, Jerry
and Garcia, both are red heads and their legs are fine. Danny and Betty lived in San Francisco
too. They both had brown hair, and Danny suffers from restless leg syndrome. Their daughter,
Cali, has dark brown hair and her legs are fine. Jerry and Cali have a son, Henry. He has red hair,
does not tan and has restless leg syndrome. Complete the family tree by assigning the genotypes
based on the phenotypes described above (Hint: obviously you can get some information from
the phenotype of the individual. Further clues can be obtained from the phenotypes of the
progeny). Use R or r for restless leg syndrome alleles or an underscore if the allele could be
either R or r. For example, R_ would represent either Rr or RR. Use M or m for the red melanin
alleles, M_ would represent MM or Mm.
A) (1.5 point) Which individuals must be heterozygous for restless leg syndrome?
B) (1.5 point) Which individuals might be heterozygous for restless leg syndrome?
C) (1 point) Which individuals must be heterozygous for the red melanin gene?
D) (2 point) Garcia marries a woman who has restless leg syndrome and red hair, what is the
probability that a child of theirs will inherit both traits? Show your logic using probability, or
draw a Punnett square to show the potential genotypes of their progeny. M S D B C H
Solution
A) Cali, Jerry; Since Henry has restless leg syndrome (rr), both of his parents should carry atleast
one copy of r allele. So, Jerry and Cali are heterozygous for the restless leg syndrome.
B) Molly and Sean; Since Both Molly and Sean have fine legs but their son is heterozygous for
the syndrome, either of them is also heterozygous for the restless leg syndrome.
C) Since Henry has red hair and no tan tendency (homozygous for red melanin gene), both of
his parents should have one copy of red melanin gene. Jerry has red hair (mm) but Cali has dark
brown hair, so, Cali is heterozygous for the red melanin gene.

2. D) Genotype of woman to whom he is married = mmrr
promability of getting mm = mm (the woman) x mm (garcia)= 1
Probabiity of getting rr= Rr x rr = 1/4
Probability of Garcia to be Rr is 1/2.
Total probability of rr = 1/4 + 1/2= 3/4
Total probability of rrmm= 3/4 x 1= 3/4