300 carries the allele for this disease. However, in some populations, including the Irish Americans, the Ashkenazi Jews and the Cajuns from Louisiana, the proportion of Tay-Sachs carriers is much higher (1 in 27 to 1 in 50) than in other populations. Which evolutionary scenario can be predicted to produce a high frequency of Tay- Sachs disease in these populations? O All three populations descend from a small number of settlers These populations experienced stabilizing selection O These populations have higher than average mutation rates These populations experienced disruptive selection The Tay-Sachs allele is advantageous at the heterozygous state

300 carries the allele for this disease. However, in some populations, including the Irish Americans, the Ashkenazi Jews and the Cajuns from Louisiana, the proportion of Tay-Sachs carriers is much higher (1 in 27 to 1 in 50) than in other populations. Which evolutionary scenario can be predicted to produce a high frequency of Tay- Sachs disease in these populations? O All three populations descend from a small number of settlers These populations experienced stabilizing selection O These populations have higher than average mutation rates These populations experienced disruptive selection The Tay-Sachs allele is advantageous at the heterozygous state

Human Biology (MindTap Course List)

11th Edition

ISBN:9781305112100

Author:Cecie Starr, Beverly McMillan

Publisher:Cecie Starr, Beverly McMillan

Chapter19: Introduction To Genetics

Section: Chapter Questions

Problem 9CT

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Tay-Sachs disease is a recessive genetic disease. Individuals with this disease rarely survive past the age of four. In the general population, approximately 1 person in 300 carries the allele for this disease. However, in some populations, including the Irish Americans, the Ashkenazi Jews, and the Cajuns from Louisiana, the proportion of Tay-Sachs carriers is much higher (1 in 27 to 1 in 50) than in other populations. Such high frequency of an otherwise rare allele is expected when Question 24 options: populations experienced disruptive selection populations were founded by a small number of settlers the allele is advantageous at the heterozygous state populations have higher than average mutation rates populations experienced stabilizing selection
Looking to the future, what changes to the frequency of the sickle-cell allele do you envision as most likely, and why? (In other words, do you envision it becoming more common or less common in human populations?) What factors (technology, climate change, etc) might be driving those changes?
Heterozygote advantage is an interesting condition in those individuals who have one of each allele (dominant and recessive) have a higher survival rate than those individuals who are either homozygous dominant or homozygous recessive. Sickle-cell anemia is such a genetic disease associated with the recessive allele. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygotes tend to…
Sickle cell anemia is caused by a recessive allele at a single gene. As we discussed in class, being a homozygote for the sickle cell allele is almost always lethal, but heterozygotes tend to be resistant against malaria although they have a mild form of anemia. Because of this heterozygote advantage, the allele for sickle cell anemia has a frequency of more than 10% in some human populations. How would present allele frequencies of the sickle cell allele change, if there was no heterozygote advantage or disadvantage (that is, that heterozygotes would be identical to ‘normal’ homozygotes – no malaria resistance, no anemia)? How would the change in sickle cell allele frequencies compare to scenario a (extirpation of malaria)
Cystic fibrosis (CF) is an autosomal recessive disorderthat occurs relatively frequently among people ofEuropean descent. In an Amish community in Ohio,medical researchers reported the occurrence of cysticfibrosis (CF) as being 1/569 live births. Using theHardy–Weinberg rule, estimate the frequency of carriers of the disease allele in this Amish population.
A curious polymorphism in human populations has to do with the ability to curl up the sides of the tongue to make a trough (“tongue rolling”). Some people can do this trick, and others simply cannot. Hence, it is an example of a dimorphism. Its significance is a complete mystery. In one family, a boy was unable to roll his tongue but, to his great chagrin, his sister could. Furthermore, both his parents were rollers, and so were both grandfathers, one paternal uncle, and one paternal aunt. One paternal aunt, one paternal uncle, and one maternal uncle could not roll their tongues.a. Draw the pedigree for this family, defining your symbols clearly, and deduce the genotypes of as many individual members as possible.b. The pedigree that you drew is typical of the inheritance of tongue rolling and led geneticists to come up with the inheritance mechanism that no doubt you came up with. However, in a study of 33 pairs of identical twins, both members of 18 pairs could roll, neither member…
Of 31 children born of father–daughter matings, 6 diedin infancy, 12 were very abnormal and died in childhood, and 13 were normal. From this information, calculate roughly how many recessive lethal genes we have,on average, in our human genomes. (Hint: If the answerwere 1, then a daughter would stand a 50 percent chanceof carrying the lethal allele, and the probability of theunion’s producing a lethal combination would be 1/2 ×1/4 = 1/8. So 1 is not the answer.) Consider also the possibility of undetected fatalities in utero in such matings.How would they affect your result?
A population of water snakes is found on an island in Lake Erie. Someof the snakes are banded and some are unbanded; banding is caused byan autosomal allele that is recessive to an allele for no bands. Thefrequency of banded snakes on the island is 0.4, whereas the frequencyof banded snakes on the mainland is 0.81. One summer, a large numberof snakes migrate from the mainland to the island. After this migration,20% of the island population consists of snakes that came from themainland.a. If both the mainland population and the island population are assumedto be in Hardy–Weinberg equilibrium for the alleles that affect banding,what is the frequency of the allele for bands on the island and on themainland before migration?b. After migration has taken place, what is the frequency of the allele forthe banded phenotype on the island?
The MC1R gene affects skin and hair color in humans.There are at least 13 polymorphisms of the gene inEuropean and Asian populations, 10 of which are nonsynonymous. In Africans, there are at least 5 polymorphisms of the gene, none of which are nonsynonymous.What might be one explanation for the differences inMC1R variation between Africans and non-Africans?
A mouse strain that has undergone inbreeding for many generations (e.b. >1000 generations) will be which of the following: O homozygous for recessive alleles at every locus O homozygous for dominant alleles at every locus O have a dominant allele at each locus, but does not have to be homozygous O may have a combination of heterozygous and homozygous loci O a mixture of dominant and recessive homozygous genotypes
Identify each of the following as an example of allele, genotype,and/or phenotype frequency:A. Approximately 1 in 2500 individuals of Northern Europeandescent is born with cystic fibrosis.B. The percentage of carriers of the sickle cell allele in WestAfrica is approximately 13%.C. The number of new mutations per generation resultingin achondroplasia, a genetic disorder, is approximately5 × 10−5.
Human geneticists have found the Finnish populationto be very useful for studies of a variety of conditions.The population is small; Finns have extensive churchrecords documenting lineages; and few people havemigrated into Finland. The frequency of some recessive disorders is higher in the Finnish population thanelsewhere in the world, and diseases such as PKU andcystic fibrosis that are common elsewhere do not occur in the Finnish population.a. How would a population geneticist explain thesevariations in disease occurrence?b. The Finnish population is also a source ofinformation for the study of quantitative traits. Thegenetic basis of schizophrenia is one question that canbe explored in this population. What advantage(s) anddisadvantage(s) can you imagine for studying complex traits based on the Finnish population structure?