Question 1

Thomas first discovered a potentially devastating piece of family history when he learned the medical diagnosis for his brother's increasing dementia, muscular rigidity, and frequency of seizures. His brother, at age 49, was diagnosed with Huntington disease (HD), a dominantly inherited condition that typically begins with such symptoms around the age of 45 and leads to death in one's early 60s. As depressing as the news was to Thomas, it helped explain his father's suicide. Thomas, 38, now wonders what his chances are of carrying the gene for HD, leading him and his wife to discuss the pros and cons of him undergoing genetic testing. Thomas and his wife have two teenage children, a boy and a girl.
What role might a genetic counselor play in this real-life scenario?

Accepted Answer

Huntington disease (HD) is an inherited dominant disorder. An affected individual might be either homozygous dominant or heterozygous dominant. 
T's brother is diagnosed with HD. The disease is late-onset at an age of about 60 years old. T. is 39 years old. There is a probability that T might inherit HD from his father. T. might be homozygous or heterozygous for the HD.
▪genetic counselor might do genetic testing of HD for T. He or she would advise T. more information about the disease, what T. needs to expect, and what aspects of his living conditions might be affected.
▪genetic counselor might help T. make plans for his future. He or she might provide him with contact information where T. could receive services and treatments.
▪genetic counselor might advise that T.'s two children might inherit HD. The genetic counselor and T. could discuss the pros and cons of doing genetic testing. The result of the genetic testing will affect T., his children, and his wife.
If the genetic test reveals T. has HD, a genetic counselor is T.'s first source of help. If T. agrees to do genetic testing, his genetic counselor would gather information from members of his families. The occurrence of HD in his family members across generations would make up T.'s pedigree.
The pedigree may be used to deduce which individuals in the pedigree would inherit HD. The pedigree might reveal the likelihood T. and his two children might have the disease.

Question 2

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
In this chapter, we focused on the Mendelian postulates, probability, and pedigree analysis. We also considered some of the methods and reasoning by which these ideas, concepts, and techniques were developed. On the basis of these discussions, what answers would you propose to the following questions:
(a) How was Mendel able to derive postulates concerning the behavior of "unit factors" during gamete formation, when he could not directly observe them?
(b) How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?
(c) In analyzing genetic data, how do we know whether deviation from the expected ratio is due to chance rather than to another, independent factor?
(d) Since experimental crosses are not performed in humans, how do we know how traits are inherited?

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Question 3

Thomas first discovered a potentially devastating piece of family history when he learned the medical diagnosis for his brother's increasing dementia, muscular rigidity, and frequency of seizures. His brother, at age 49, was diagnosed with Huntington disease (HD), a dominantly inherited condition that typically begins with such symptoms around the age of 45 and leads to death in one's early 60s. As depressing as the news was to Thomas, it helped explain his father's suicide. Thomas, 38, now wonders what his chances are of carrying the gene for HD, leading him and his wife to discuss the pros and cons of him undergoing genetic testing. Thomas and his wife have two teenage children, a boy and a girl.
How might the preparation and analysis of a pedigree help explain the dilemma facing Thomas and his family?

Accepted Answer

A pedigree is like a map that reveals affected individuals, which are suffering with Huntington disease (HD). It consists of individuals from several generations. It includes members of a nuclear family and extended families. In T.'s case, his pedigree will include his father, brother, siblings, and other relatives from his side and his wife's side of the family.
The preparation of the pedigree requires T. to gather information from his family members and other more distant relatives. T. and his genetic counselor would have to work together to create the pedigree.
The pedigree might have missing information if T. and his genetic counselor could not obtain the information for several relatives. The missing information might affect the accuracy of the pedigree analysis.
The analysis of the pedigree reveals the probability that T. and his children inherit Huntington disease (HD). The dilemma in knowing this probability is that there is a chance they have HD. There is a chance they do not have HD.
They might not have time to prepare for the effects of HD if they do not know they inherit the disease. On the other hand, they might not have the disease. 
The plan based solely on life with HD may be entirely different than life with HD. T.'s children might decide not to have children of their own because they do not want to pass on the disease to their children.
However, T.'s children may not get the disease when they are in their 60s. On the other hand, not knowing the probability of inheriting HD may lead T. and his children to be unprepared for life with HD.
T.'s children may have the disease and have children of their own. Consequently, T.'s children may have HD.
There are pros and cons in knowing and not knowing the probability of inheriting HD. Each individual's life choice may be based solely on the effects of HD or it may be based on other factors too.
T. and his family must make choices based on the science information, their plans for the future, the supports they would have, and other factors in life.

Question 4

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Review the Chapter Concepts list. The first five concepts provide a modern interpretation of Mendelian postulates. Based on these concepts, write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.
CHAPTER CONCEPTS
▪Inheritance is governed by information stored in discrete factors called genes.
▪Genes are transmitted from generation to generation on vehicles called chromosomes.
▪Chromosomes, which exist in pairs in diploid organisms, provide the basis of biparental inheritance.
▪During gamete formation, chromosomes are distributed according to postulates first described by Gregor Mendel, based on his nineteenth-century research with the garden pea.
▪Mendelian postulates prescribe that homologous chromosomes segregate from one another and assort independently with other segregating homologs during gamete formation.
▪Genetic ratios, expressed as probabilities, are subject to chance deviation and may be evaluated statistically.
▪The analysis of pedigrees allows predictions concerning the genetic nature of human traits.

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Question 5

Thomas first discovered a potentially devastating piece of family history when he learned the medical diagnosis for his brother's increasing dementia, muscular rigidity, and frequency of seizures. His brother, at age 49, was diagnosed with Huntington disease (HD), a dominantly inherited condition that typically begins with such symptoms around the age of 45 and leads to death in one's early 60s. As depressing as the news was to Thomas, it helped explain his father's suicide. Thomas, 38, now wonders what his chances are of carrying the gene for HD, leading him and his wife to discuss the pros and cons of him undergoing genetic testing. Thomas and his wife have two teenage children, a boy and a girl.
If Thomas decides to go ahead with the genetic test, what should be the role of the health insurance industry in such cases?

Accepted Answer

Treatments and services provided to patients with Huntington disease (HD) are likely to be very expensive. Insurance companies that cover payments for the treatments and services of HD may provide policy holder several options.
One option might be, to increase the premium policy for the holders. Another option might be, to supplement the cost with other less expensive health care plans.
The health insurance industry might provide rules that applied to everyone before people sign up for health insurance. The rules would give people the options and risks in deciding which health insurance plan is best for them.
For example, the health insurance industry might provide several different types of health insurance. Each type of health insurance would have different premium.
For example: In health insurance plan A, an individual may pay a very high premium. This health insurance plan would cover all treatments and services for all illnesses and diseases known and unknown.
This health insurance plan would cover the cost of treatments and services should T. inherited HD. However, he would pay too much in premium. If it turns out that he will not get HD in his 60s, then he would have overpaid the insurance company.
In health insurance plan B, an individual is required to get genetic testing for only several diseases, including HD. Based on the results of the genetic testing, the health insurance company would determine the premium.
T.'s genetic test may reveal that he does not have the genes for HD. That is, his probability of inheriting HD is low. Health insurance plan B would be far less expensive than health insurance plan A.
There is also another advantage with T. sign up for health insurance plan B. If T. develops symptoms and effects characteristics of HD in his early 60s, then health insurance plan B would cover the expenses for his treatments and services. He is not required to pay the higher premium like in health plan A.
Health insurance plan C would enable individuals to decide, which diseases and illnesses policy holders want to be covered. T. can choose his health plan to cover the expenses for HB before getting any genetic testing.
The health insurance plan C would be less expensive than plan A, but may be more expensive than Plan B. For instance, T. does not have HB in his 60s, but he has other diseases. His health insurance plan C may cover the expenses of other diseases up to a certain amount.
However, T. will have all expenses for HB covered if he has only HB in his early 60s. He would still pay the same premium.
Health insurance plan D would require everyone to do genetic testing for diseases. A health insurance company may provide bonuses and premium discount per disease tested.
T. may pay higher in higher premium with plan D than plan C if the genetic tests reveal that he also has high probability of getting other diseases. However, he would be covered for those diseases as well. The discounts and bonuses he receives may be more than he would pay if he chooses plan C.
Health insurance plan poses risk to both policy holders and insurance companies. The cost of treatments and services may be expensive for both policy holders and insurance companies. 
Therefore, policy holders and insurance companies should take risk and make choices. The options should take into account the interests and welfare of both the insurance companies and the policy holders.

Question 6

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)(a) Two normal parents have five children, four normal and one albino.
(b) A normal male and an albino female have six children, all normal.
(c) A normal male and an albino female have six children, three normal and three albino.
(d) Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).

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Question 7

Thomas first discovered a potentially devastating piece of family history when he learned the medical diagnosis for his brother's increasing dementia, muscular rigidity, and frequency of seizures. His brother, at age 49, was diagnosed with Huntington disease (HD), a dominantly inherited condition that typically begins with such symptoms around the age of 45 and leads to death in one's early 60s. As depressing as the news was to Thomas, it helped explain his father's suicide. Thomas, 38, now wonders what his chances are of carrying the gene for HD, leading him and his wife to discuss the pros and cons of him undergoing genetic testing. Thomas and his wife have two teenage children, a boy and a girl.
If Thomas tests positive for HD, and you were one of his children, would you want to be tested?

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Question 8

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Which of Mendel's postulates are illustrated by the pedigree that you constructed in Problem? List and define these postulates.
Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)(a) Two normal parents have five children, four normal and one albino.
(b) A normal male and an albino female have six children, all normal.
(c) A normal male and an albino female have six children, three normal and three albino.
(d) Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).

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Question 9

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Discuss how Mendel's monohybrid results served as the basis for all but one of his postulates. Which postulate was not based on these results? Why?

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Question 10

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
What advantages were provided by Mendel's choice of the garden pea in his experiments?

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Question 11

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F 1 plants had round seeds with yellow cotyledons. Diagram this cross through the F 2 generation, using both the Punnett square and forked-line, or branch diagram, methods.

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Question 12

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Based on the preceding cross, what is the probability that an organism in the F 2 generation will have round seeds and green cotyledons and be true breeding?

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Question 13

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? State the postulate.

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Question 14

In a cross between a black and a white guinea pig, all members of the F, generation are black. The F2 generation is made up of approximately 3/4 black and 1/4 white guinea pigs. 
(a) Diagram this cross, showing the genotypes and phenotypes. 
(b) What will the offspring be like if two F2 white guinea pigs are mated? 
(c) Two different matings were made between black members of the F2 generation, with the following results.
  
Diagram each of crosses.

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Question 15

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
What is the basis for homology among chromosomes?

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Question 16

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
In Drosophila , gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P 1 individuals are homozygous, work the following crosses through the F 2 generation, and determine the genotypic and phenotypic ratios for each generation.
(a) gray, long × ebony, vestigial
(b) gray, vestigial × ebony, long
(c) gray, long × gray, vestigial

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Question 17

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
How many different types of gametes can be formed by individuals of the following genotypes: (a) AaBb , (b) AaBB , (c) AaBbCc , (d) AaBBcc , (e) AaBbcc , and (f) AaBbCcDdEe ? What are the gametes in each case?

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Question 18

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Mendel crossed peas having green seeds with peas having yellow seeds. The F 1 generation produced only yellow seeds. In the F 2 , the progeny consisted of 6022 plants with yellow seeds and 2001 plants with green seeds. Of the F 2 yellow-seeded plants, 519 were self-fertilized with the following results: 166 bred true for yellow and 353 produced an F 3 ratio of 3/4 yellow: 1/4 green. Explain these results by diagramming the crosses.

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Question 19

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
In a study of black guinea pigs and white guinea pigs, 100 black animals were crossed with 100 white animals, and each cross was carried to an F 2 generation. In 94 of the crosses, all the F 1 offspring were black and an F 2 ratio of 3 black:1 white was obtained. In the other 6 cases, half of the F 1 animals were black and the other half were white. Why? Predict the results of crossing the black and white F 1 guinea pigs from the 6 exceptional cases.

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Question 20

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. 
Mendel crossed peas having round green seeds with peas having wrinkled yellow seeds. All F 1 plants had seeds that were round and yellow. Predict the results of testcrossing these F 1 plants.

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Quiz 3: Mendelian Genetics

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. What advantages were provided by Mendel's choice of the garden pea in his experiments?

When working out genetics problems in this and succeeding chapters, always assume that members of the P 1 generation are homozygous, unless the information or data you are given require you to do otherwise. What is the basis for homology among chromosomes?