Question

3. Sickle-cell disease is a genetic condition caused by an autosomal recessive allele which al- fects one in every 500 African American children born in the U.S. One in every ten African Americans is a carrier for the recessive allels. Although sickle cell disease is caused by a single human gene, it is expressed through many different effects throughout the body. The presence of a recessive sickle-cell allele in humans causes the red blood cells to produce abnormal hemoglobin protein molecules which can link together and crystalline. This in turn causes the red blood cells to take on a sickle-shaped form with jagged edges, which can become destroyed by the body, clog the flow of blood in small blood vessels, and accumulate in the spleen. Multiple organs are damaged over time, and 100,000 people who are homozygous recessive die each year from this disease worldwide. a. David and Linda want to start a family but are concerned about sickle-cell disease, since both of them have relatives who died from this disorder. They decide to make an appoint- ment with you, a well-known genetic counselor. What would be the first step you recom- mend to this couple? b. When the results of the genetic tests come back, you see that David is indeed a carrier for this condition, while Linda does not have a copy of the gene. At their follow-up visit. David is concerned about his carrier status. Complete the Punnett square below to show the probability of David and Linda having a child with sickle-cell disease. Use the letter "A" to symbolize this gene. Sperm Eggs David and Linda have % chance of having a child with sickle-cell disease. c. Suppose that both David and Linda had turned out to be carriers. Complete the Punnett square below to show the probability of David and Linda having a child who is also het- erozygous. Sperm d. Circle the heterozygous genotypes in the Punnett square.

Answer 1

Amwa a) The couple will be first advised to go for genetic screening of codon 6 mutation of B- globin (elusval mutation). b) Now if is not elaborate Linda will David is a carrieq and the following funnett square me results of mating: A A (linda) | AA LAA a Aa Aal (David). David and Linda have % chance of having a child with sickle-cell disease. . (). The following Punnett square will elaborate me outcome, if bom parents (David & Linda) are carriers. AAAA Probability of beterrazten heterozygoms children (Aa) have been . d). The . circled.