1. A child is born with a common genetic disease. Neither of the child\'s parent
ID: 274332 • Letter: 1
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1. A child is born with a common genetic disease. Neither of the child's parents has the disease. (a) Is the disease caused by a dominant or recessive allele? Explain. (1 pt) (b) What is the chance (expressed as a percentage or a fraction) that the same parents will have a child who has a normal genotype with no disease alleles? (0.5 pt) 2. In cats, curly hair is rare but is an inherited trait. Every kitten with curly hair has at least one parent with curly hair. (a) Is curly hair determined by a dominant allele or a recessive allele? Explain your answer. (1 point) (b) Using whatever symbol you like, list all the possible genotypes for cats with curly hair and all the possible genotypes for cats with straight hair. (0.5 point) 3. (1 point) Consider the number of cats with short hair or with long hair in the cat population (the photo set) that you saw in lab. Assume that the photos of different phenotypes accurately represent the frequency of traits in a real cat population. Can you tell whether the allele for short hair or the allele for long hair is dominant? Explain your reasoning. (1 pt) 4. In cats, the B gene controls hair color (the dominant B allele = black, and the recessive b allele -brown). The S gene controls spotting (the dominant S allele - white spots, and the recessive s allele- no spots). The D gene controls the density of hair pigment. The recessive d allele allows the full color of the B and b alleles to show. The dominant D allele dilutes the color so that black color becomes gray, and brown color becomes tan. For each cat shown below, identify the possible genotype(s) for the B, S, and D genes. (Be sure to view the document in color.) (0.5 point each) 5. If you wanted to determine the genotype of the gray and white cat (the third cat shown above), you could do a test cross. What is the genotype and phenotype of the second cat you would use for the test cross? (1 pt)Explanation / Answer
Ans 1) (a) The disease has been caused by the recessive allele. In this, the parents are the carrier of one copy of the recessive disorder and with this, the child has 25% of being affected by the disorder. The disease in the child is caused due to the expression of the diseased recessive allele.
(b) The chance that with each pregnancy the child will be unaffected but a carrier of the disorder by 50%. However, the chances that the child will not be a carrier are around 25%.
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