Concept explainers
CASE STUDY|A genetic flip of the coin
On July 11, 2008, twin sons were born to Stephan Gerth from Germany and AddoGerth from Ghana. Stephan is very fair-skinned with blue eyes and straight hair; Addo is dark-skinned, with brown eyes and curly hair. The first born of the twins, Ryan, is fair-skinned, with blue eyes and straight hair; his brother, Leo, has light brown skin, brown eyes, and curly hair. Although the twins' hair texture and eye color were the same as those of one or the other parent, the twins had different skin colors, intermediate to that of their parents. Experts explained that the blending effect of skin color in the twins resulted from quantitative inheritance involving at least three different gene pairs, whereas hair texture and eye color are not quantitatively inherited. Using thisas an example of quantitative genetics, we can ask the following questions:
Would twins showing some parental traits (hair texture, eye color) but a blending of other traits (skin color in this case) seem to be a commonplace event, or are we looking at a “one in a million” event?
Want to see the full answer?
Check out a sample textbook solutionChapter 21 Solutions
Essentials of Genetics Plus Mastering Genetics with eText -- Access Card Package (9th Edition) (Klug et al. Genetics Series)
- Hemophilia and color blindness are both recessive conditions caused by genes on the X chromosome. To calculate the recombination frequency between the two genes, you draw a large number of pedigrees that include grandfathers with both hemophilia and color blindness, their daughters (who presumably have one chromosome with two normal alleles and one chromosome with two mutant alleles), and the daughters sons. Analyzing all the pedigrees together shows that 25 grandsons have both color blindness and hemophilia, 24 have neither of the traits, 1 has color blindness only, and 1 has hemophilia only. How many centimorgans (map units) separate the hemophilia locus from the locus for color blindness?arrow_forwardThe following pedigree shows the pattern of inheritance of red green color blindness in a family. Females are shown as circles and males as squares; the squares or circles of individuals affected by the trait are filled in red. What is the chance that a son of the third-generation female indicated by the arrow will be color-blind if the father is a normal man? If the father is color-blind?arrow_forwardIn mammals, albinism is caused by an autosomal allele that interferes with skin pigment. Early one morning on your way to genetics class, you observe that two normally pigmented javelina parents have an albino piglet. What are the genotypes of the parents? _________________________________ What is the probability that their next five offspring will be albino? __________________________ What is the probability that 3 of the next 7 offspring will be normally colored?______________________ Describe the process by which you would test these normally colored offspring to see if they carried the albinism gene. What are the expected ratios from that test? You want to develop a strain of albino javelina for commercial use (the other really white meat). Describe how you would go about developing that strain starting with the 2 parents and the one albino offspring.arrow_forward
- 10 cM separates two hypothetical autosomal human genes. The dominant alleles are have complete penetrance and will result to Crossed eyes (e+) and short thumbs (th+). Four children are born to a normal guy and cross-eyed, small-thumbed woman. Two of the children have short thumbs and the other two have crossed eyes. She is carrying her fifth child. What is the probability that this fifth child will be cross-eyed and have short thumbs?arrow_forwardTay-Sachs disease is a rare human disease in which toxic substances accumulate in nerve cells. The recessive allele responsible for the disease is inherited in a simple Mendelian manner. For unknown reasons, the allele is more common in populations of Ashkenazi Jews of eastern Europe. A woman is planning to marry her first cousin, but the couple discovers that their shared grandfather’s sister died in infancy of Tay-Sachs disease.a. Draw the relevant parts of the pedigree, and show all the genotypes as completely as possible. b. What is the probability that the cousins’ first child will have Tay-Sachs disease, assuming that all people who marry into the family are homozygous normal?arrow_forwardDog coat color genetics is actually more complicated that what is described for the Labrador dog example in your textbook. One gene locus, the A locus, has a dominant allele (AS, which gives hairs that are solid black, and aw, which is agouti (a wolf-like gray). As you know, the B locus is responsible for the difference in color between black (B-) and brown or chocolate (bb) Labradors. You also know that Labrador dogs also come in a yellow coat color. a) Set up a simple cross or set of genetic crosses that falsify the idea of the 3 colors of Labrador dogs being due to a simple multiallelic series, with black dominant to brown which is dominant to yellow.arrow_forward
- Working with the definitions of penetrance and expressivity, analyze the following pedigree and assume that the father of the proband is homozygous for a rare trait. (Consider a rare trait here to be less than 1 in 30,000.) What pattern of inheritance other than autosomal recessive could explain this pedigree? In particular, explain the genotype and phenotype of the proband (arrow).arrow_forward1) By convention, the recessive trait will determine the abbreviation used to track crosses if it is a mutant condition, since it stands out in contrast to the rest of the population. For example, if pea pods are typically green in color, a mutant condition might result in yellow pea pods; therefore, the lowercase letter ‘y’ would be used to depict the mutant state, yellow, while uppercase ‘Y’ would depict the wildtype (wt) condition, green. Remember that the mutant condition is not necessarily always recessive. 1 A) . If green is dominant wt (Y) and yellow is a recessive mutant condition (y), depict a Yy father mated with a YY mother in the Punnett. 1B) Considering the dominant allele, what colors are the parents in the cross above? Yy = _____________________ YY = _____________________ 1C) What colors are the offspring in the cross above? 1D) What is the phenotypic ratio of the offspring? 1E) What is the genotypic ratio of the offspring? (Remember, the genotypic ratio is based…arrow_forwardYou are a gene hunter, trying to find the genetic basis for a rare inherited disease. Examination of six pedigrees of families affected by the disease provides inconsistent results. For two of the families, the disease is co-inherited with markers on chromosome 7. For the other four families, the disease is co-inherited with markers on chromosome 12. Explain how this difference might have arisen.arrow_forward
- Punnet square problems A=Codominant; B=Codominant; O=Recessive Mary is homozygous for type A blood. Steve is homozygous for type O blood. If they have children, what are the possible phenotypes and genotypes of their children, and what is the probability of each? Mary and Steve have a son, Brad. Brad’s wife, Samantha is heterozygous for type B blood. If they have children, what are the possible phenotypes and genotypes of their children, and what is the probability of each? Stella loves roses and decides to cross her red rose with her white rose. All of the resulting offspring of this cross are pink roses. What can you say about the red and white alleles as a result of this cross? Stella decides to cross two of the pink roses. What are the possible genotypes and phenotypes of the offspring and the probabilities of each? DNA replication, Transcription and Translation problems It is S phase of the cell cycle, and time to replicate the cell’s DNA. Using the following strand of DNA…arrow_forwardNeo-Mendelian Genetics: Complete dominance and overdominance Huntington’s disease, a neurodegenerative genetic disorder that typically becomes noticeable in middle age, is due to an autosomal dominant allele. Sickle cell anemia, on the other hand, is a genetic blood disorder due to a recessive allele. Mary is a carrier of the allele for sickle cell anemia but has no sign of any neurodegenerative disorder in her family. She married Paul whose father died of Huntington’s disease. His mother, however, is not inflicted with that condition. Neither of his parents exhibits sickle cell anemia. What are the genotypes of Mary and Paul? If they plan to have four children, what is the probability that: all their children will be normal? ____________ they will have a son with Huntington’s disease? ___________ they will have a daughter inflicted with both conditions?____________arrow_forward71. Myotonic Dystrophy, Fragile X, and Huntington disease are examples of human genetic diseases that exhibit earlier ages of onset and/or an increased severity in afflicted members of each successive generation in families in which the mutant alleles are segregating. These are both examples of genetic diseases which exhibit: a. partial penetrance. b. incomplete dominance. c. genetic imprinting. d. genetic anticipation. \arrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage LearningBiology: The Dynamic Science (MindTap Course List)BiologyISBN:9781305389892Author:Peter J. Russell, Paul E. Hertz, Beverly McMillanPublisher:Cengage Learning