Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.
Determine the alleles for the NF1 gene and the DNA marker gene on each chromosome carried by the four family members in generation I and generation II. Use N for the dominant NF1 allele and n for the recessive allele and assume I-1 is heterozygous for the disease allele (Nn).

Question

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.

What is the estimated recombination frequency between the NF1 gene and the DNA marker?

Pedigree chart showing NF1 gene segregation with darkened symbols for affected individuals and DNA marker genotypes.

Determine the alleles for the NF1 gene and the DNA marker gene on each chromosome carried by the four family members in generation I and generation II. Use N for the dominant NF1 allele and n for the recessive allele and assume I-1 is heterozygous for the disease allele (Nn).

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next problem. It says blank is a type of physical mapping in which high molecular weight DNA is digested using a restriction enzyme with a few restriction sites. And our answer choices are a micro satellite mapping. B radiation, hybrid mapping mapping, C fish capital F I S H mapping and D macro restriction mapping. Well, we actually have a clue in the name right here. We're looking for a type of mapping where there's very large DNA, high molecular weight DNA digested using what we would call rare cutter enzymes. So restrictions enzymes that only have a few restriction sites. So chopping up these big pieces of DNA into smaller but still large pieces. And what we're looking for is macro restriction mapping. And again, we have a clue right. In the name, we have macro, meaning large and restriction, referring to those restriction enzymes. And this macro restriction mapping is a sort of rough approach to looking at the location of genes in large um whole portions of DNA and large portions of chromosomes. Um It involves cutting the fragments by those rare cutter restriction enzymes and then using gel electrophoresis to separate those fragments by size. And then you the pattern of these size fragments can be used to create a physical map that depicts the relative placement of genes and by the sizes of those fragments. And it's effective in mapping DNA molecules large regions of them. So whole chromosomes or genomic regions. But again, obviously low resolution, it's also useful when sequencing is not possible or too expensive. Um again, breaking that down and sort of rough general locations of things in these very large pieces. Let's take a look at our other answer choices to understand why they're not correct choice. A is micro satellite mapping. And this is a different approach to mapping that uses the short tandem repeats in DNA, those highly repetitive pieces of DNA in which certain motifs are repeated 5 to 50 times and they occur in thousands of locations throughout the genome and have a much higher rate mutation rate than other DNA and therefore vary in individuals. These are the kind of regions that are used in DNA fingerprinting, distinguishing one individual from another because they vary so much. So that's kind of the most common usage we know of these um these little repeat segments, but they can be used in mapping. And that's because many of these are found within genes of known or geat function. So these little repeated regions called microsatellites or short tandem repeats, the regions that occur within these genes of known function. Can actually be used to link genetic maps of related species. So you can almost use them as little little labels of these known genes and track them across different species and use them to help make maps of other species DNA based on DNA regions we already know. So that's what that micro satellite mapping is. But it's not this mapping of high molecular mot DNA with restriction enzyme, cutting it into fragments. So it's not our correct answer. So we can eliminate that. Then there's choice B radiation hybrid mapping. And this one is quite different from our macro restriction uh mapping in this technique. This is a technique for mapping mammalian cell. The mammalian DNA excuse me in which the chromosomes are broken into segments using x-rays. These segments are then cloned in rodent cells. And as you examine the DNA in those cells, the location of different genes on either the same or separate fragments. So you've chopped your chromosomes up into fragments, gives you an idea of the distance between those genes. So genes that are closer together are more likely to end up more often on the same fragment. After that DNA has been broken up. Whereas genes farther apart, of course, more often will end up on separate fragments. So another form of chopping up the DNA and then looking at things but a different method. So not our answer. And then finally choice C F I S H mapping, fish mapping just gonna put our little description down at the bottom here since I'm running out of space and that involves using and here you have fluorescence labeled probes. That's what the F is from fluorescent N C two hybridization. And those probes are for specific DNA sequences, they can be labeled with different colors of fluorescence. And then those probes bind to chromosomes bind to their complementary sequence on the chromosomes and then their locations on the chromosomes can actually be visualized. You see where the fluorescence is and you can see the physical location of the gene. So that's what that technique is. But again, not the one we're looking for in our answer. So not our answer choice. So again, we have choice. D macro restriction mapping is the type of physical mapping in which high molecular weight DNA is digested using a restriction enzyme with a few restriction sites. See you in the next video.

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Key Concepts

Autosomal Dominant Inheritance

Genetic Linkage and Markers

Pedigree Analysis