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27 Sep 2018

Imagine that you have a particular genetic trait and that you have four children. Two of the four children also possess this trait. Meanwhile, the other biological parent of your children does not possess the trait.

Explain why you think the trait in the scenario is dominant or recessive.

Based upon your response, describe why it would or would not be possible for the trait in the scenario to âskipâ a generation.

Patterns of inheritance within organisms like pea plants, fruit flies, mice, and others are somewhat easy to determine since their mating practices can easily be controlled. Apart from controlling who mates with whom, what other characteristics make species like these ideal for studying genetics?

Select and describe a health problem that you believe has a genetic component at least partially inherited. If you do not identify an inherited health condition within your family, choose a disease that interests you or impacts a friend or other family member. Would you be interested in having genetic testing to determine whether you carry a genetic mutation for a particular disorder or a genetic predisposition for a disease? Why/why not? What are the advantages and disadvantages of determining your predisposition?

Explore the current state of research for the health problem you selected. Focus on one of the following to discuss as they relate to the genetics of the disease:

Cause

Testing/Screening/Prevention

Treatments/Therapies/Cures

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Jarrod RobelLv2

29 Sep 2018

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1.) This summer, there was a surge in the number of albino children killed for their body parts in the African country of Malawi (yes, it's bizarre but sadly true: http://goo.gl/8o0imm and http://goo.gl/DK0r8M). Albinism in humans is inherited as a simple recessive trait. Assuming that two non-albino (normal) parents have five children, four of which are normal and one of which is albino, which of the following statements is true? Select all that apply (you must select all correct answers to get credit). Assume that 'A' indicates the non-albino allele and 'a' indicates the albino allele.

Multiple answers:You can select more than one option

A)The 4 normal children are heterozygous Aa

B)At least one of the normal siblings must be homozygous AA

C)The frequency of albino children is as expected for Mendelian inheritance

D)One of the parents cannot be Aa

E)One third of the normal children expected to be AA while the others Aa

2.)

Albinism in humans is inherited as a simple recessive trait. Assuming that a normal male and an albino female have 6 children, all normal, which of the following statements is true? Select all that apply (you must select all correct answers to get credit).

Multiple answers:You can select more than one option

A)The father could be heterzygous for the trait

B)The probability that all the children are heterozygous for the trait is (1/2)^5 = 1/32

C)The father cannot be Aa

D)The children should all be heterozygous for the trait

E)One would expect about 2/3 of the normal children to be Aa

F)The father must be AA

3.)

Given an albino male mating with a normal female to produce 3 normal children and 3 albino children, which of the following of Mendel's postulates are not being demonstrated by this particular scenario? Select all that apply (to get credit, all your choices must be correct).

Multiple answers:You can select more than one option

A)Postulate of segregation

B)Postulate of dominance

C)Postulate of independent assortment

D)Postulate of unit factors

4.)

Consider the cross: Ee ff Gg HH x Ee Ff gg HH (assume these are designations for genes that are inherited in a Mendelian fashion). What is the probability that a single offspring from this cross would be genotypically: ee Ff Gg HH or Ee ff gg HH?

A)1/16

B)1/32

C)9/64

D)1/6

E)3/16

F)27/64

G)1/64

H)3/64

I)1/8

J)3/8

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 30âs.

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
Lauraâs (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) âCFTR gene DNA sequenceâ. You will see an alignment of the NIH human genome sequence of the CFTR gene â called âReferenceâ rather than âwild-typeâ- 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 â-â 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 â-â 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?

1. Characters that show a continuous range of variation, such as height and eye color, usually are controlled:

a.	by a single gene with two alleles that are codominant.

b.	by many genes with an additive effect.

c.	by epistatic interactions between two genes.

d.	mainly by the environment, with only a small genetic component.

2. In humans, red-green colorblindness is inherited as a sex-linked recessive trait. In order for a woman to be red-green colorblind, which of the following statements must be true.

a.	Her mother must be red-green colorblind.

b.	All of her brothers must be red-green colorblind.

c.	Her father must be red-green colorblind.

d.	All of the above statements must be true if a woman is red-green colorblind.

3. The x-ray crystallography data collected by Rosalind Franklin suggested to Watson and Crick that the:

a.	structure of DNA is a double helix.

b.	two strands of the DNA molecule are joined by hydrogen bonds between the bases.

c.	four bases within DNA pair in a specific way.

d.	two strands of the DNA molecule are joined by covalent bonds between the bases.

4. In the genetic code, _________ one amino acid.

a.	one nucleotide specifies

b.	two nucleotides specify

c.	three nucleotides specify

d.	four nucleotides specify

5. During Meiosis I, a homologous pair of chromosomes may not separate, resulting in daughter cells that have extra chromosomes or are missing chromosomes. This can lead to genetic disorders, including Down Syndrome. This phenomenon is called:

a.	independent assortment.

b.	nondisjunction.

c.	segregation.

d.	crossing over.

6. You are a human geneticist studying the incidence of retinitis pigmentosa in the residents of Tristan de Cunha, a group of small islands in the middle of the southern Atlantic Ocean. The allele for retinitis pigmentosa, which causes a form of blindness, is inherited as an autosomal recessive. You have determined that the frequency of this allele (r) in the population is 0.4 (40%). Using the principles of the Hardy-Weinberg rule, you would estimate the frequency of individuals who are heterozygous for this allele (Rr) in the population to be:

a.	0.16 (16%)

b.	0.24 (24%)

c.	0.36 (36%)

d.	0.48 (48%)

7. Natural selection acts at the level of the:

a.	phenotype.

gene.

c.	population.

d.	nucleotide.

8. You are working with pea plants, trying to recreate the experiments that Mendel performed. You are doing a dihybrid cross with a plant that is heterozygous for both seed shape and seed color, with the genotype RrYy. Which allelic combinations would you expect to find in the gametes produced by this plant?

a.	This plant would produce only RY and ry gametes.

b.	This plant would produce only RrYy gametes.

c.	This plant would produce RY, Ry, rY, and ry gametes.

d.	You cannot determine which gametes this plant can produce without knowing the genotypes of its parents.

9. Biochemist Erwin Chargaff found that in DNA there is a special relationship between the four bases that we now call Chargaff's rule. His observation was that, in an organism's genome the:

a.	percentage of A nucleotides = the percentage of T nucleotides, and the percentage of C nucleotides = the percentage of G nucleotides.

b.	four bases all occur in an equal frequency (25%) within each organism.

c.	percentage of A nucleotides = the percentage of G nucleotides, and the percentage of C nucleotides = the percentage of T nucleotides.

d.	genetic material is composed of proteins, not DNA.

10. During DNA replication:

a.	each strand of the double helix acts as a template for the synthesis of a new strand.

b.	the enzyme DNA polymerase adds nucleotides to the strand being synthesized.

c.	the bases A,C,G and T are required.

d.	All of the above are true of DNA replication.

11. During translation, amino acids are joined by peptide bonds to make polypeptides. The formation of these peptide bonds is catalyzed by:

12. If an allele (R) at a gene with two alleles shows complete dominance, individuals with the genotypes ______ will have the same phenotype.

a.	RR and rr.

RR and Rr

Rr and rr

d.	Each of the three possible genotypes will have a different phenotype.

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