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# Genetic Variations

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1. Duchenne muscular dystrophy (DMD) is an X-linked disease for which prenatal diagnostic testing can be performed. Has prenatal genetic testing increased the detection rate of this disease, compared to prior diagnostic methods? If so, how? If not, why? In case the fetus is diagnosed with DMD and parents decide to terminate the pregnancy, are there chances that the next child will also be a carrier of the disease?

2. Jane Hill's husband, Charlie Marlow, has hemophilia A when he marries Hill, who does not have the disorder. Jane's parents also do not have hemophilia, but her brother Steve Hill does. What is the probability that the Marlows' son will have the disorder? What is the probability that their daughter will have hemophilia? Are there chances that their daughter will be a carrier of this disorder?

https://brainmass.com/health-sciences/disease-outbreak-control/genetic-variations-563357

#### Solution Preview

1. Genetic testing can detect Duchenne Muscular Dystrophy (DMD) if a known mutation is present. Prenatal genetic testing has increased the rate of DMD detection. The following article, http://www.nature.com/ejhg/journal/v21/n1/full/ejhg2012101a.html, discusses the lack of DNA testing for female fetuses. However, due to their possible carrier ability, the author felt this policy needs to change. Another option for DMD detection is neonatal testing. This is also discussed in the ...

#### Solution Summary

This solution discusses the transmission of X-linked diseases by providing external information sources as well as a PowerPoint presentation with diagrammatic explanations.

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## Genetic variation and disease

1 Define the term "genetic variation."

If a gene or locus has two alleles (A and a) in a population, what are all the possible genotypes?

If the frequency of (A) allele = p, and the frequency of (a) allele is q, what is the frequency of all possible genotypes in this population?

2 What is the Hardy-Weinberg equilibrium?

In a population, a locus A has two alleles (A) and (a). The frequency f of (A) is f (A) = 0.6; what is the f (a)?

Using these frequencies, calculate the frequencies of all possible genotypes in a population in Hardy-Weinberg equilibrium.

3 In a population (Z), the frequencies of genotypes of a two allele locus (B and b) are f(BB) = 0.3, f(bb) = 0.6, f (Bb) = 0.1. Calculate the frequencies of both alleles.

Using the allele frequencies calculated in a., calculate the frequencies of all possible genotypes at this locus in a population after one generation of random mating.

Is the population (Z) in part a above in Hardy-Weinberg equilibrium? The population size is 1000.

4 Describe how you would use the Hardy-Weinberg equilibrium to calculate genotype frequencies of a locus with three alleles.
If the f(D) of an X-linked gene in a population = 0.8, what is the f(d) of the other allele at this locus?

What is the frequency of females' homozygous for d allele (XdXd)?

What is the frequency of males' hemizygous for the d allele (XdY)?

5 Explain why more males present with X-linked recessive diseases. Show your reasoning.

Why must the five assumptions/criteria apply to a population before we can say it is in Hardy-Weinberg equilibrium?

Take any one of these assumptions and explain in detail how it could disrupt the Hardy-Weinberg equilibrium for a particular gene locus.

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