1 Biology 321 Spring 2013 Assignment Set #5 â Be sure to work through the last two problems. Note that these questions test your reading comprehension and understanding of terminology as well as your knowledge of genetics. ââ Required Reading and Assigned Problems in Textbook Chapter 2 Examine solved problem 1 Work problems 48, 73, 78 Chapter 6 Reread this chapter solved problem 1 Work problems 12 & 63 Required Problem Assignments in 9th edition of text http://fire.biol.wwu.edu/trent/trent/assignmentset5.9.pdf Additional problems Ì Problem 1 The symptoms of the disease state hereditary hemochromatosis result in an accumulation of iron in various tissues of the body, leading to failure of liver function, tumors, diabetes, and arthritis. This autosomal disease can be easily treated -- periodic blood-letting is sufficient. In young adults, only men are affected; in older individuals, women are affected as well. In Europe, individuals with this disease state may show less severe symptoms than in America where meat consumption is higher. This is a single-gene trait. Circle the term or terms that apply to this trait: a. incompletely dominant f. modifier gene b. pleiotropic c. sex-linked g. polymorphic d. sex-influenced h. haploinsufficient e. epistatic i. variably expressive2 ❖ Problem 2 The following pedigree was taken from a recent publication on the genetics of familial male precocious puberty (a very rare trait). Individuals with this syndrome generally show signs of puberty by age 4. Choose the best conclusion from the choices below: a. The gene for this trait must be located on the Y chromosome. b. This trait probably is sex-linked recessive, with the mothers of affected males being carriers. c. This trait is likely to be autosomal dominant with the sex ratio skewing due to chance. d. This is an autosomal dominant trait showing sex-limited inheritance. 12121234112233445567IIIIIIIVV ❖ Problem 3 Individuals of identical phenotype may have different genotypes, and vise versa” Is this statement true or false? Explain using the appropriate genetic terminology. ❖ Problem 4 In Siamese cats, a temperature-sensitive albino mutation is responsible for the beautiful coloration of these animals. This mutation, though, also plays havoc with the neurology of the Siamese visual system: the development of the nerves linking retina and brain are affected. Based on this information, the albino mutation is: a. pleiotropic b. epistatic c. incompletely penetrant d. recessive lethal e. incompletely dominant3 ❖ Problem 5 The pedigree shown is of streaked hairlessness in Holstein-Friesian cattle, a condition characterized by an abnormality of the hair coat in which narrow, irregular hairless streaks, running transversely around the trunk, appear. Affected females were mated with normal males (not shown) How can you explain this pattern of inheritance? Try to come up with at least two different explanations. Which one is most likely? Give reasons for your decision. ❖ Problem 6 Individuals with Tourette syndrome exhibit a neuropsychiatric disorder characterized by chronic motor and vocal tics that begin in childhood. The tics involve a compelling urge to perform rapid, sudden movements or vocalizations. Studies suggest that TS is inherited as an autosomal dominant trait. Surprisingly, monozygotic twin pairs often show considerable phenotypic variability with respect to expression of this trait. • Does this observation contradict the statement that this is an inherited disease state? Briefly explain your answer. • Be sure to list the general factors that influence expression of a trait and for each, determine if it is likely to be an explanation for the variable expressivity. Briefly explain by giving hypothetical explanations/examples that are relevant to the specifics of this disease trait. ❖ Problem 7 A woman, whose father is normal, has a rare autosomal dominant disease. This trait shows about 90% penetrance in heterozygotes. If this woman marries a normal man, what is the probability that their first child will NOT have the disease? a. 0 b. 0.5 c. 1.0 d. 0.55 e. 0.45 f. 0.95 ❖ Problem 8 Two genes are involved in determining the color of the foxglove flower. The dominant allele of the M gene produces a light magenta pigment. The dominant allele of the D gene causes a darkening of the pigment produced by the M gene, resulting in dark magenta flowers. The D gene is therefore: a. epistatic to the M gene b. dominant to the M gene c. shows variable expressivity d. is a modifier gene e. none of these answers apply to the D gene4 ❖ Problem 9 The hormone leptin is an important physiological regulator of several endocrine functions in humans. Leptin acts through the leptin receptor. Mutations in the leptin receptor result in early onset morbid obesity, failure to develop secondary sexual traits and reduced levels of growth hormone. Similar phenotypes are caused by mutations in the obese gene which codes for the leptin hormone itself. In the family shown in the pedigree below, a mutant allele of the leptin receptor gene fails to produce functional mRNA. Individuals known to be heterozygous (from direct DNA testing) for the leptin receptor mutation have normal phenotypes. This mutant allele was not observed in a control group of 402 individuals. Based on the information given, next to each term indicate: A if the term applies to the leptin receptor mutation and associated phenotype C if the information given outright contradicts the term I if there is insufficient information to determine whether the term applies ____incomplete dominance ___haploinsufficient ____variable expressivity ____incomplete penetrance ____polymorphic ____autosomal recessive ____X-linked dominant ____sex-limited/sex-influenced ____ pleiotropic ____ loss-of-function W= weight in kg H= height in cm BMI and FM are measures of body fat5 ❖ Problem 10 The pedigree shown below shows the inheritance of blue sclera (the thin outer wall of the eye and brittle bones. These phenotypic variations are result of the same mutant allele which is very