Download Genetics Lab Cystic Fibrosis Cystic fibrosis is a serious genetic

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Transcript
Genetics Lab
Cystic Fibrosis
Information source:
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/cftr.shtml
Cystic fibrosis is a serious genetic disorder caused by a deletion
mutation, ΔF508, of the CFTR (cystic fibrosis transmembrane
conductance regulator) gene located on chromosome 7.
The normal CFTR protein product is found in membranes of cells
that line passageways of the lungs, liver, pancreas, intestines,
reproductive tract, and skin. The protein helps cells keep salt in
balance.
When the normal protein is synthesized by ribosomes, the Golgi
apparatus transports it along the endoplasmic reticulum for
packaging. If the protein is normal the Golgi apparatus sends it to
the membrane where it can control active transport of chloride.
When a CFTR protein with a ΔF508 mutation reaches the endoplasmic reticulum, the ER
recognizes the protein as defective and marks it for recycling. As a result the protein
never becomes part of the membrane.
Individuals who are heterozygous for the ΔF508 mutation are called carriers. An
individual who inherits two alleles with the ΔF508 mutation will have cystic fibrosis and
he or she will build up a dangerous thick sticky mucus coating along the lungs and
digestive organs.
Barbie and Ken have been referred to the lab by their daughter Sally’s pediatrician for
cystic fibrosis testing. No one in Barbie or Ken’s families has cystic fibrosis.
Sally’s DNA sequence and m-RNA transcription are shown below. Translate the m-RNA
into t-RNA. Use the amino acid chart to convert the t-RNA to amino acids. Compare
Sally’s amino acid sequence to the normal amino acid sequence.
Normal Amino Acid Sequence
Ile Ile Phe Gly Val
506 507 508 509 510
Sally’s Gene Segment
DNA
ATC
ATT
GGT
GTT
ACT
m-RNA
UAG
UAA
CCA
CAA
UGA
t-RNA
Amino acid
Does Sally have cystic fibrosis? Explain your diagnosis.
Use the chart of find the amino acid coded by the transfer RNA.
ΔF508 Pedigree Chart
Roberts Family
Bill
Ann
Midge
Carson Family
Skipper
Dan
Karen
Barbie
Ken
Jill
Brad
Sally
The Roberts and Carson families were tested for the ΔF508 mutation. The results are
shown on the pedigree chart. Fill in Sally’s result based on your testing.
Construct a Punnett Square for Ann and Bill and for Karen and Dan. Use C for the
dominant normal allele and c for the recessive defective allele.
Dan
Karen
Ann
Bill
What were the chances of Ann and Bill having a child with cystic fibrosis?
What were the chances of Karen and Dan of having a child with cystic fibrosis?
Why didn’t cystic fibrosis appear in earlier generations?
Barbie and Ken have been referred to you for genetic counseling. What can you tell them
based on Punnett Square analysis?
Errors During Meiosis
Meiosis is the cell division process that ends with four daughter cells with half of the
normal chromosomes. In humans, the egg cells and sperm cells undergo meiosis to form
four haploid (half number) gametes.
Sometimes errors occur during the division process that result in cells with an additional
chromosome or a deleted chromosome. Usually gametes with an unusual number of
chromosomes simply do not have the opportunity to become an embryo.
Although meiosis errors may occur in sperm cells, the greater number of meiosis errors
occur in egg cells. Chromosome errors during meiosis are more common among women who
conceive after age 40, but can occur at any age.
Amniocentesis is a screening process that uses a sample of the amniotic fluid surrounding
the developing fetus to determine a karyotype. Organizing the chromosomes into pairs
creates a karyotype. The table below shows some common syndromes caused by known
abnormalities.
Syndromes
Abnormality
Occurrence per 10,000
births
Lifespan (years)
Down’s
Trisomy 21
15
40
Edward’s
Trisomy 18
3
<1
Patau’s
Trisomy 13
2
<1
Turner’s
Monosomy X
2 (female births)
30-40
Kleinfelter’s
XXY
10 (male births)
normal
Source: http://genome.wellcome.ac.uk/doc_wtd020854.html
You have received an amniocentesis sample from an obstetrician. Analyze the karyotype.
Report the gender of the fetus and any abnormality. If there is an abnormality, identify
the syndrome.
Gender
Abnormality
Syndrome
Duchenne Muscular Dystrophy
Information source: http://yourgenesyourhealth.org/dmd/whatisit.htm
Duchenne muscular dystrophy is the most common form of muscular dystrophy. It occurs
more frequently in boys than in girls. The symptoms of muscle weakness begin between 3
and 5 years of age with a rapid progression of weakness. By age 12, most affected boys
are unable to walk. Muscle weakness will progress to the respiratory muscles requiring
the use of a ventilator in the final stages.
Symptoms of Duchenne muscular dystrophy are caused by the absence of dystrophin, a
protein involved in maintaining the integrity of muscle. The gene that codes for
dystrophin is located on the X chromosome.
Kevin and Karen Emmitt have come to you for genetic counseling. Karen had a brother
who died from Duchenne muscular dystrophy. Kevin has no history in his family. Their
chromosome analysis has been used to construct a Punnett square.
XM normal allele
Xm muscular dystrophy allele
Duchene MD is a condition caused by an
X-chromosome linked recessive allele.
Karen Emmitt
Analyze the Punnett Square of the Emmett Family and then answer the questions. NOTE:
Probability is based on four possible outcomes. Express your answer as a percentage
Kevin Emmett
XM
Y
XM
XM XM
XM Y
Xm
XM Xm
Xm Y
If the couple has a daughter, what is the probability
that the couple will have a daughter with MD?
If the couple has a daughter, what is the probability
that the couple will have a daughter who is a carrier
of MD?
If the couple has a son, what is the probability that
the couple will have a son with MD?
Is it possible for a son to be an MD carrier? Explain.
Why are males more likely to have MD than females? Explain.