Sicklecell anemia is caused by a mutation in the human globi

Sickle-cell anemia is caused by a mutation in the human -globin gene. The three possible genotypes are homozygous for normal -globin, heterozygous carrier (having both the normal and sickle - cell alleles), and homozygous for sickle cell anemia. Recombinant DNA technology has been used as the basis for prenatal diagnosis of sickle cell anemia. In a very high percentage of the cases observed, the normal human -globin gene is carried on a 7600 bp human DNA fragment from a HpaI digest, while the sickle-cell gene is carried on a 13000 bp HpaI fragment.

Available to you are:

A labeled sample of recombinant DNA consisting of a bacterial plasmid vector (4000 bp) carrying the 7600 bp HpaI fragment from the normal human genome.

A sample of genomic DNA from each member of a couple thought to be carriers of the sickle-cell trait and expecting their first child.

A sample of the genomic DNA obtained from the fetal cells in the amniotic fluid from the uterus of the pregnant woman.

1. You perform a Southern on HpaI digested DNA using the recombinant plasmid as a probe. What sized band (s) would you expect in each of the following cases?

a. Heterozygous carrier mother

b. Homozygous normal mother

c. Homozygous for sickle cell anemia fetus

d. Combined genomic DNA from a heterozygous carrier mother + homozygous normal

father

Please help!!

Solution

In order to determine the southern blot pattern, first we need to determine the genotype of the given phenotypes of the parents.

a) Heterozygous carrier mother (Xh X) : A carrier female will have one normal and one sickle cell allele

b) Homozygous normal mother (X X): A female with both normal alleles.

c) Homozygous for sickle cell anaemia fetus (Xh Xh) : Both sickle cell alleles.

d) Xh X + X X

Based on the above genotype, the expected results are:

a) one band of normal allele (7600 bp) and one band of sickle cell allele (13000) bp

b) one band of normal allele (7600 bp)

c) one band of sickle cell allele (13000 bp)

d) one band of normal allele and band of sickle cell allele