Although only 2% of people worldwide have naturally blond hair, this percentage

Question

Although only 2% of people worldwide have naturally blond hair, this percentage increases to 80% some regions of Scandinavia. The highest prevalence of blond hair outside of Europe occurs in the Solomon Islands (5-10% of islanders are blond), a cluster of islands in Oceania near Australia. Different mutations in different genes are associated with blond hair in these different populations and the mutations occurred after these populations were isolated from each other.

The questions below are taken from data from two research articles which explore the origins of blond hair (some of the data have been modified so they make sense to you).

In Europeans, one of the mutations most strongly associated with blond hair occurs not within a coding sequence but in an enhancer located 355 kilobase pairs upstream of the gene KITLG. KITLG encodes a signaling protein, Kit, that regulates the pigment production pathway (under-production of Kit leads to white hair). In blond Solomon Islanders, there is a mutation in the coding region of the gene TYRP1, which encodes the pigmentation enzyme tyrosinase-related protein 1.

Questions 1 and 2:

Many blond Europeans have a single point mutation upstream of the KITLG gene. A strain of mouse known as Steel Panda has very light-colored fur (mouse on the right in the figure below) as a result of a different mutation in the region upstream of the KITLG gene. In this case, x-ray exposure caused a double strand break in the chromosome. The broken section was repaired by re-ligating it back into the chromosome, but in the reverse orientation.

1:

Which mutation is likely to alter the sequence of the Kit protein?

Question 1 options:

The point mutation in blond Europeans

The x-ray irradiation induced mutation in the Steel Panda mice.

neither a or b

2:

Imagine that one of these mutations does not alter the sequence of the Kit protein. Which of the following mechanisms could account for the “blond” phenotype?

Question 2 options:

Deletion of the KITLG promoter

Activation of the KITLG promoter

No expression of Kit protein

Normal expression of the Kit protein

Overexpression of Kit protein

Excision of the KITLG gene from its promoter

The point mutation in blond Europeans

The x-ray irradiation induced mutation in the Steel Panda mice.

neither a or b

Explanation / Answer

1. B The x-ray irradiation induced mutation in the Steel Panda mice.

The mutation is due to inversion of the DNA in the coding region. X-ray irradiation is responsible for breaking the DNA strand, the repair mechanisms religated the broken fragment in the reverse orientation.

2. A, C, and F

The blond pheonotype is due to underexpression of the Kit protein. This may occur either due to deletion of the KITLG promoter, lack of expression of Kit protein, or excision of KITLG gene from its promoter.

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