Log in
Biology
2
answers
0
watching
28
views

Cystic fibrosis (CF) is an inherited chronic disease that affects the lungs and digestive system of about 30,000 children and adults in the United States. It is caused by a recessive allele that encodes a defective chloride channel. Genetic screening has determined that two parents are carriers (heterozygous for CF). What is the probability that they have a child with CF?

Watch
2
answers
0
watching
28
views

For unlimited access to Homework Help, a Homework+ subscription is required.

Unlock all answers

Get 1 free homework help answer.
Get unlimited access
Already have an account? Log in
Share
Nelly Stracke
Nelly StrackeLv2
27 Apr 2019
Get unlimited access
Already have an account? Log in
Share

Related textbook solutions

Molecular Cell Biology
8 Edition,
Lodish
ISBN: 9781464183393
Biology: Science for Life with Physiology
6 Edition,
Belk
ISBN: 9780134555430
Biology
2nd Edition, 2013
Openstax
ISBN: 9781947172517
Concepts of Biology
OER Edition,
Openstax
ISBN: 9781938168116
Essentials of Biology
5 Edition,
Mader
ISBN: 9781259660269

Related questions

Cystic Fibrosis (CF) is an autosomal recessive genetic disease that is characterized by the secretion of thick, abnormal mucous in the lungs. The mutated gene that leads these symptoms is the CF transmembrane conductance regulator (CFTR gene). The encoded protein is a chloride channel that moves chloride ions out of epithelial cells. In a homozygous individual, the lack of this chloride channel function in a mutant slows the flow of water into extracellular spaces. This lack of water export leads to the heavy mucus in the lungs of CF patients. Although children with CF would die in childhood, current treatments provide life expectancies into the 30’s.

CF is the most frequently inherited genetic disorder among American children. It affects 1 of every 2,500 children; 30,000 currently have the disease. Although its frequency is higher in European populations, it affects all human populations. Heterozygous carrier frequencies in the US are estimated to be 1 out of 29 Caucasians, 1 out of 46 Hispanics, 1 out of 61 African Americans and 1 out of 90 Asians. There are genetic screens for carriers of CF but they are not routinely performed despite this high frequency of carriers. At least all states in the US proscribe testing of newborns to identify children with CF early so that treatment can be started. Newborn tests for CF: http://www.cff.org/AboutCF/Testing/NewbornScreening/ScreeningforCF/ . If CF is such a common genetic disease, and such a simple Mendelian trait, why is genetic screening of parents not done more frequently? Is it just economic, a pain to do, or is it more complex such that the results of genetic testing are not just positive or negative?

Answer the following questions:
1. If two parents are heterozygous carriers of CF, show a pedigree with four children showing the incidence of carriers and afflicted children. If each unafflicted child (carrier or not) mates with another person, who has a 1 out of 30 chance of being a carrier of CF, what is the expected incidence CF disease in the third generation (frequency of CF in any one of grandchildren of the original couple)?

2. Pleiotropy of Cystic Fibrosis. Watch the two videos on the left at:

http://www.cftrscience.com/MOD-animation
or, if you can not view these, read the short NIH Genetics Home Reference for Cystic Fibrosis http://ghr.nlm.nih.gov/condition/cystic-fibrosis

Connect the description with one of the following videos, or related ones (there are many) you see:
video (10 minutes) of daily life of a child with Cystic Fibrosis http://www.youtube.com/watch?v=WUsuGKzdDg8
Laura’s (20 year old) video diary of life with CF http://www.youtube.com/watch?v=Pgrf8qJXhpc&feature=related

In your own words, describe the range of CF phenotypes. List the other organs besides lungs that are affected and how does it affects those organs.

3.The DNA sequence of the CFTR gene is 170,000 base pairs in length and encodes the CFTR protein that is 1480 amino acids long. Open the accompanying text file (in Canvas/Files/Discussion folder) “CFTR gene DNA sequence”. You will see an alignment of the NIH human genome sequence of the CFTR gene – called “Reference” rather than “wild-type”- against a gene sequence containing a common mutation in CFTR. Look at the alignment and determine how the DNA sequence differs between them. What is the position number where they differ? How many and what nucleotides do they differ in? A “-“ mark in one sequence in the alignment means that that base sequence is missing the corresponding bases in the other sequence. The sequence is a long one but the differences are in bolded bright red text. Matching sequence is marked with a | linking the two sequences. Look near the sequence AAATATCATC if you use FIND tool in Word.

In another file, you will an alignment of the reference translated into a protein sequence, compared to the mutant allele translated into protein sequence. The differences are again in red whereas the areas where the proteins match are in black. Look at the alignment. How do these two proteins differ? Again, find the position number and describe how they differ at that location. A “-“ mark in the alignment means that amino acid is missing when compared to the other sequence.

4. Given that the CFTR gene can be analyzed for a mutation that causes CF, couples interested in being tested as carriers face several choices given the results.
What could be a consequence of a false positive result (couple is identified as carriers but they would not produce any children with symptoms)?

What could be a consequence of a false negative result (a test indicates the couple is not both carriers but they would produce some children with CF)?

5. The sensitivity of the test can vary with ethnic group. The following is a chart from the NCBI Genetic testing site. A sensitivity less than 100% would be likely to produce false negative results from an inability to determine that someone is carrier.

CF Carrier Test Sensitivity by Ethnic Group
http://www.ncbi.nlm.nih.gov/projects/GeneTests/static/concepts/primer/ptscarr5.shtml

Ethnic Group 1

Population Frequency of CF

Sensitivity of Carrier Detection 2

Caucasian

1 in 29

90%

Ashkenazi Jewish

1 in 29

97%

Native American

1 in 32

94%

Latino

1 in 46

57%

African-American

1 in 60

75%

Asian

1 in 90

30%

Why might different ethnic populations differ in the ability of the genetic test to identify carriers of CF?

Cystic fibrosis (CF) is caused by a genetic mutation resulting in defective proteins in secretory cells, mainly in the epithelial lining of the respiratory tract. The one in every 2,000 Caucasian babies who has the disease is homozygous for the recessive mutant. Although medical treatment is becoming more effective, in the past, most children with CF died before their teens. About 20 Caucasian in 2,000 are carriers of the trait, having one mutant and one normal allele, but they do not develop the disease. According to rules of population genetics, the frequency of the homozygous recessive genotype should be rarer than it is. What is one possible explanation for the unusually high frequency of this allele in Caucasian population?

1) You have been hired as a genetic counselor. Your first patient is a young woman named Lei who comes to you because her brother has cystic fibrosis. (Learn more about this disease in the PowerPoint slides – find out how it is inherited, is it dominant or recessive?) Lei is healthy but would like to know the risk that she is a carrier for the disease. Both her parents are healthy as is her older sister. a. Fill in the Punnett Square below with her parent’s genotypes to predict her risk of being a carrier of cystic fibrosis. You should be able to determine her parent’s genotypes from information given above. Male/ Female b. Explain to Lei her risk of being a carrier: 2). A blood DNA test for the cystic fibrosis allele becomes available and you recommend to Lei that she take the blood test and that her Fiancé Robert take the test as well. Lei’s test shows that she is a carrier. Robert is not. What is the risk that their future child will have cystic fibrosis? a. Use the Punnett Square below to predict Lei and Robert’s risk of having a child with CF? Male/ Female b. Write down your explanation to Lei and her Fiancé: 3. Another patient, Mark, comes to you because his father has just been diagnosed with the rare genetic disorder known as Huntington’s disease. Mark would like to know his potential risk of developing the disease (you must read about the inheritance pattern of Huntington’s disease in the Lecture and online games to answer this correctly!). Assume that his mother is showing no signs of Huntington’s disease. a. Fill in the Punnett Square below to predict Mark’s risk of getting Huntington’s disease. Male/ Female b. Your explanation to Mark:

Weekly leaderboard

Home
Homework Help 3,900,000
Biology 460,000
Start filling in the gaps now
Log in