Can someone help me understand how to read a restriction map? Thanks! RFLPs can
ID: 191257 • Letter: C
Question
Can someone help me understand how to read a restriction map? Thanks!
RFLPs can be used to follow the inheritance of specific chromosomal regions. Under certain circumstances, RFLPs that are near a defective gene can be used to determine whether the deleterious gene is present in an unborn child.
A concerned couple has come to you for genetic counseling. Their second child (triangle) died shortly after birth from an inherited genetic disease, and the mother is pregnant again. Their first child is unaffected. The deceased child was the second individual in the family lineage to be affected: a brother of the paternal grandmother of the child was the other. The couple wishes to know whether their unborn child has this genetic disease. You have studied the genetics of this disease and know that it is caused by an autosomal recessive gene. The chromosomal region, in which the disease gene is located, has several restriction-site polymorphisms within the population as a whole, as indicated in the restriction map (Figure A). The restriction-site polymorphisms in the population are indicated with a +/- designation (+, restriction site is present; -, restriction site is absent). It is important that you understand this figure in order to correctly answer the question.
You isolate DNA samples from both parents, both sets of grandparents, and the unaffected child and characterize them by restriction mapping, as shown in the genealogy (Figure B). The bands that are dark mean that there are more molecules of that DNA fragment compared to the bands that are lighter in intensity. There are only two band intensities - light and dark.
Remember that each of us has an autosomal chromosome from our mother and an autosomal chromosome from our father so at any one locus one may be homozygous or heterozygous - we are diploid!
What restriction pattern (combination of bands) will indicate to you that the fetus is likely to be have inherited and will likely be affected by the disease?
A Presence of bands 1, 2, 6, and 9 kb
B Presence of bands 2, 6, and 9 kb
C Presence of bands 2, 4, and 6 kb
D Presence of bands 1, 2, and 9 kb
E Presence of bands 4, 5, and 6 kb
F Presence of bands 1 and 9 kb
G Presence of bands 6 and 9kb
(A) RESTRICTION MAP kb (B) GENEALOGY maternal lineage paternal lineage grandparents o- parents children kb 6 2Explanation / Answer
it is quite easy to read a plasmid map. First thing you need to imagine is to join both ends of the map together to form a single circular DNA. consider the restriction sites at both ends to be the single one and then try to solve the problem.
The upper arrow shows the presence of restriction sites where the DNA can be cut while the lower arrows shows the distance between each restriction site.
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