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#Question id: 5654

Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when a small deletion in a specific region of chromosome 15 is contributed by either the father or mother, respectively. Why does this small deletion not behave as a recessive allele for either syndrome, that is, why is its loss not made up for by the good copy of the region on chromosome 15 contributed by the other parent?

#Unit 5. Developmental Biology

This portion of chromosome 15 is invariably mutated, so the other parent contributes recessive alleles that are thus homozygous and perturb development.
The copy of chromosome 15 from the other parent has genes in the region of the deletion that are imprinted, and thus inactive; in the absence of any active copies of these genes, development cannot proceed normally.
The genes in this portion of chromosome 15 are special in that they are required in two copies for normal development, and so the loss of one set does not allow normal development.
Chromosomes with deletions do not go through mitosis correctly, so cell divisions in the embryo result in cells with abnormal numbers of chromosomes, and these cells do not contribute properly to the development of the organism.

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#Question id: 3832

#Unit 3. Fundamental Processes

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). Which two classes of DNA do these different samples represent?

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#Question id: 17996

#Unit 8. Inheritance Biology

Consider a heritable autosomal disease with an incidence in the population of 1 per thousand. On average, individuals with the disease have 80% as many children as the population average. In answering the various parts of this question, assume that mating is random. Now assume that the mutation rate is zero, that the disease is recessive, and that the disease allele is maintained in the population by heterozygote advantage. Calculate the heterozygote advantage,

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#Question id: 31175

#Unit 7. System Physiology – Animal

Excitatory postsynaptic potential (EPSP) is produced through excitatory transmitter which opens:

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#Question id: 4868

#Unit 8. Inheritance Biology

A mouse cross C/c . D/d X c/c . d/d is made, and in the progeny there are