Concept explainers
Canavan disease, caused by homozygosity for a recessive allele, is a severe neurodegenerative syndrome usually resulting in death by the age of 18 months. The frequency of Canavan disease is particularly high in Jewish populations. In an effort to map the gene causing this condition, researchers looked at 10 SNPs (1–10) spaced at roughly 100 kb distances along chromosome 17 in five affected Jewish patients (Cases) and four unaffected Jewish individuals (Controls). In the accompanying table, each row depicts a single haplotype. (Every individual is diploid and therefore has two haplotypes, although only one is shown in the table.) G, C, A, and T represent the actual
Case | SNP1 | SNP2 | SNP3 | SNP4 | SNP5 | SNP6 | SNP7 | SNP8 | SNP9 | SNP10 |
1 | G | T | G | T | T | T | C | A | G | T |
2 | A | T | G | T | T | T | C | A | G | T |
3 | G | T | G | T | T | T | C | A | G | C |
4 | A | A | G | T | T | T | C | T | C | C |
5 | G | A | G | C | C | T | G | A | C | C |
Control | ||||||||||
6 | A | A | G | T | T | T | C | A | G | T |
7 | G | T | G | G | C | T | G | A | G | T |
8 | A | T | C | T | C | G | C | T | C | C |
9 | G | T | C | G | T | G | G | A | C | T |
a. | Does the disease-causing mutation appear to be in linkage disequilibrium with any of the SNP alleles? If so, which ones? |
b. | Where is the most likely location for the Canavan disease gene? About how long is the region to which you can ascribe the gene? |
c. | How many independent mutations of the Canavan gene are suggested by these data? |
d. | Suppose that individuals 2–9 are Ashkenazic (whose ancestors lived in the Rhine river basin of Germany and France after the Jews were expelled from Judea in 70 A.D.) while individual 1 is Sephardic (a non-Ashkenazic Jew). Would these facts provide any information about the history of the mutations causing Canavan disease? |
e. | For mapping genes by haplotype association, why is it often helpful to focus on certain subpopulations? Does this strategy have any disadvantages? |
f. | Human chromosome 17 is an autosome, so each person has two copies of each region along the chromosome. With this in mind, explain the practical difficulty in determining haplotypes. (Hint: Consider heterozygosity.) In light of this difficulty, how could the researchers determine any individual haplotype, such as any of those shown in the table? |
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Chapter 22 Solutions
ND STONY BROOK UNIVERSITY LOOSELEAF GENETICS: FROM GENES TO GENOMES
- In a particular country in sub-Saharan Africa, a medical study revealed that 0.075% of the country's population are suffering from sickle-cell anemia. Sickle cell disease is caused by a mutation in the haemoglobin-Beta gene found on chromosome 11. Sickle cell anemia is controlled by a pair of alleles, H and h, where the individuals with the illness have the homozygous recessive genotype; those with normal red blood cells have the alternative genotype. Using the Hardy-Weinberg's equation, calculate the percentage of the population of the two genotypes for normal blood cells. In a few remote areas in that country, the percentage of sickle cell anemia reaches as high as 5%. Calculate the percentage of homozygous and heterozygous individuals with the normal blood cells and find the ratio for both phenotypes.arrow_forwardUsing figure 1 and the following background information answer the following questions. Identification of the genetic cause of hornlessness in cattle has been the subject of intensive genetic and genomic research, culminating in the nomination of two different candidate neomutations on cattle chromosome 1 that are predicted to have arisen 500-1,000 years ago: a complex allele of Friesian origin (PF), an 80,128 base pair (bp) duplication (1909352–1989480 bp), and a second, simple allele of Celtic origin (PC) corresponding to a duplication of 212 bp (chromosome 1 positions 1705834–1706045) in place of a 10-bp deletion (1706051–1706060)We report the use of genome editing using transcription activator-like effector nucleases (TALENs) to introgress the putative PC POLLED allele into the genome of bovine embryo fibroblasts to try and produce a genotype identical to what is achievable using natural mating, but without the attendant genetic drag and admixture. In our previous studies, we…arrow_forwardSix months pregnant, an expectant mother had a routine ultrasound that showed that the limbs of the fetus were unusually short. Her physician suspected that the baby might have a genetic form of dwarfism called achondroplasia, an autosomal dominant trait occurring with a frequency of about 1 in 27,000 births. The parents were directed to a genetic counselor to discuss this diagnosis. In the conference, they learned that achondroplasia is caused by a mutant allele. Sometimes it is passed from one generation to another, but in 80 percent of all cases it is the result of a spontaneous mutation that arises in a gamete of one of the parents. They also learned that most children with achondroplasia have normal intelligence and a normal life span. 1. What information would be most relevant to concluding which of the two mutation origins, inherited or new, most likely pertains in this case? How does this conclusion impact on this couple’s decision to have more children? 2. It has been…arrow_forward
- The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings and long bristles. Mutant strains have been isolated that have either curled wings or short bristles. The genes representing these two mutant traits are located on separate chromosomes. Carefully examine the data from the following five crosses shown below (running across both columns). (a) Identify each mutation as either dominant or recessive. In each case, indicate which crosses support your answer. (b) Assign gene symbols and, for each cross, determine the genotypes of the parents.arrow_forwardOrangutans are an endangered species in their natural environment (the islands of Borneo and Sumatra), and so a captive-breeding program has been established using orangutans currently held in zoos throughout the world. One component of this program is research into orangutan cytogenetics. This research has shown that all orangutans from Borneo carry one form of chromosome 2, as shown in the accompanying diagram, and all orangutans from Sumatra carry the other form. Before this cytogenetic difference became known, some matings were carried out between animals from different islands, and 14 hybrid progeny are now being raised in captivitya. What term or terms describe the differences between these chromosomes? b. Draw the chromosomes 2, paired in the first meiotic prophase, of such a hybrid orangutan. Be sure to show all the landmarks indicated in the accompanying diagram, and label all parts of your drawing. c. In 30 percent of meioses, there will be a crossover somewhere in the region…arrow_forwardOrangutans are an endangered species in their natural environment (the islands of Borneo and Sumatra), and so a captive-breeding program has been established using orangutans currently held in zoos throughout the world. One component of this program is research into orangutan cytogenetics. This research has shown that all orangutans from Borneo carry one form of chromosome 2, as shown in the accompanying diagram, and all orangutans from Sumatra carry the other form. Before this cytogenetic difference became known, some matings were carried out between animals from different islands, and 14 hybrid progeny are now being raised in captivity.q3.1 q2.2 q2.1 q1.2 q1.1Borneop1.1 p1.2cenq3.1 q2.2 q2.1 p1.1Sumatrap1.2cenq1.1 q1.2a. What term or terms describe the differences between these chromosomes?b. Draw the chromosomes 2, paired in the first meiotic prophase, of such a hybrid orangutan. Be sure to show all the landmarks indicated in the accompanying diagram, and label all parts of your…arrow_forward
- Using the figure and the following background information answer the following questions about the figure Background: Identification of the genetic cause of hornlessness in cattle has been the subject of intensive genetic and genomic research, culminating in the nomination of two different candidate neomutations on cattle chromosome 1 that are predicted to have arisen 500-1,000 years ago: a complex allele of Friesian origin (PF), an 80,128 base pair (bp) duplication (1909352-1989480 bp), and a second, simple allele of Celtic origin (PC) corresponding to a duplication of 212 bp (chromosome 1 positions 1705834-1706045) in place of a 10-bp deletion (1706051-1706060)We report the use of genome editing using transcription activator-like effector nucleases (TALENs) to introgress the putative PC POLLED allele into the genome of bovine embryo fibroblasts to try and produce a genotype identical to what is achievable using natural mating, but without the attendant genetic drag and admixture. In…arrow_forwardSusan’s grandfather was deaf, and passed down a hereditary form of deafness within Susan’s family as shown in Figure Q19–12.A. Is this mutation most likely to be dominant or recessive?B. Is it carried on an autosome or a sex chromosome? Why?C. A complete SNP analysis has been done for all of the 11 grandchildren (4 affected, and 7 unaffected). In comparing these 11 SNP results, how long a haplotype block would you expect to find around the critical gene? How might you detect it?arrow_forwardThe Hemoglobin gene has two very common alleles: HbS and HbA. Bob’s professor asks him to draw the chromosomes for an individual that is HbSHbA and label the alleles. Bob draws this (below). Explain why Bob is wrong and then draw it correctly. FOXP2 is a gene in humans; humans that have mutated copies of FOXP2 often have trouble speaking. It is on Chromosome 7, which is about 160 million base pairs long. FOXP2 is at position 115 million base pairs. Which of the drawings below appropriately diagrams the location of FOXP2? Why?arrow_forward
- An STR on chromosome 5 is very closely linked to a gene involved in a dominant metabolism disorder (one one copy of the mutation causes the disease). There are four different alleles of the STR (Q, B, S, and L), each with different numbers of GATCTCG repeats. The S allele has 2 repeats, the B allele has 7 repeats, the Q allele has 10 repeats, and the L allele has 5 repeats. Part 1 Lane 1 of the gel shown below indicates the locations of PCR products corresponding to all four STR alleles when run together in one lane. DNA was loaded into the wells at the top of the gel. Move the letter of each allele to its correct position at the left of Lane 1 to indicate where each allele runs on the gel. 0000 Gabriel Andre Lane 1 O Maria Andre Maria Juliana B L Part 2 Andre and Maria are the parents in this family; all others shown on the gel are children. Daughter Juliana is born with the metabolism disorder, but daughter Camila does not have the disorder. Assuming no recombination between the STR…arrow_forwardConcordance studies of twins for a neurodegenerative disorder show MZ= 46% and DZ= 15%. Further studies have shown a possible link to a gene on chromosome 9, however, there are some individuals in the study who have the allele but do not develop the disorder (group 1), and there are other individuals who do not have the allele yet develop the disorder (group 2). Amita's older sister and maternal uncle have this disorder. Currently, Amita & her 2 younger brothers do not show symptoms. Amita's paternal grandfather was rumored to have this disorder. 1. Draw the pedigree for Amita's family and determine the mode of inheritance if any. 2. Explain how the 2 groups in the study could be possible? 3. What would you tell Amita about the heritability of this disorder?arrow_forwardA haplotype is a set of DNA variations, or polymorphisms, that tend to be inherited together. A haplotype can refer to a combination of alleles or to a set of single nucleotide polymorphisms (SNPs) found on the same chromosome. Each SNP represents a difference in a single nucleotide. For example, an SNP may replace the cytosine (C) with thymine (T) in a certain stretch of DNA. SNPs occur normally throughout a person’s DNA. They occur almost once in every 1,000 nucleotides on average, which means there are roughly 4 to 5 million SNPs in a person's genome. These variations may be unique or occur in many individuals; Most commonly, these variations are found in the DNA between genes. They can act as biological markers, helping scientists locate genes that are associated with disease. When SNPs occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function. Nucleotide Position…arrow_forward
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