You have been characterizing the gene responsible for chronic hereditary ear hai

Question

You have been characterizing the gene responsible for chronic hereditary ear hair disorder by mapping restriction enzyme sites in the gene. The coding region of the gene contains a single Hind III site, but no Eco RI sites (there will be sites for both outside the gene in the other genomic DNA). At this point, you want to clone the gene so you can study it further and use it as a probe. The plasmid you want to use contains the ampicillin resistance gene, which has a Hind III site within it, and the tetracycline resistance gene, which has an Eco RI site within it. Describe the steps you would take to clone the intact gene.

Chronic hereditary ear hair disorder (CHEHD) is a recessive trait. The recessive allele differs from the wild-type allele by only a single point mutation, which conveniently falls within the Hind III site. The mutation changes the DNA sequence within the site such that Hind III does not recognize and cut the sequence. Utilizing this information, you obtain blood samples from five newborn subjects, and isolate their DNA. You cut the DNA with Hind III, and perform a Southern blot on the DNA, using your cloned gene as a probe. The following bands show up on the Southern blot:

CHEHD Southern Blot State the genotype of each of the newborns, and indicate which you expect to develop the heartbreak of CHEHD, and why.

Explanation / Answer

Chronic hereditary ear hair disorder (CHEHD) is a recessive trait. The recessive allele differs from the wild-type allele by only a single point mutation, which falls within the Hind III site. The mutation changes the DNA sequence within the site such that Hind III does not recognize and cut the sequence. Therefore, if DNA from persons with Chronic hereditary ear hair disorder (CHEHD) is added with Hind III enzyme, the enzyme cannot recognise its recognition site and therefore the DNA is uncut. Among the 5 children analysed by Southern blot analysis, the DNA sample fromchildren 1 and 3 remained uncut. Being heavy compared to cut DNA, they have moved slowly. Children 2 and 5 showed 2 bands.So, they must be homozygous for normal allele. Child 4 shows three bands. Therefore one of the allele is recessive and one is dominant.

The genotype of each of the newborn is shown below,

1 - homozygous recessive

2 - homozygous dominant

3 - homozygous recessive

4 - heterozygous (contains both dominant and recessive allele)

5 - homozygous dominant

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