Deck 2: Mendelian J Nheritance

Question 1

Why did Mendel's work refute the idea of blending inheritance

Answer 1

The work of Mendel refuted the idea of blending inheritance. Because the test conducted by him was on the phenotypic expression of pea-pod colors. The tests never resulted in yellow-green pea-pods; their colors were all either yellow or green.

Question 2

Describe three advantages of using pea plants as an experimental organism.

Answer 2

The advantages for selecting pea plant as experimental plant are as follows:
• It has only two alleles. Lower the number of alleles, greater the scope of observing changes in the alleles.
• It can grow faster and easily. The faster growth aid in getting quick results.
• They produce offsprings, which have ability to self-fertilize. The self-fertilization in offsprings will avoid any involvement of foreign alleles.

Question 3

What is the difference between cross-fertilization and self-fertilization

Answer 3

The concept of cross-fertilization and self-fertilization are the same, as sexual reproduction and asexual reproduction.
In the case of plants, cross-fertilization occurs when the pollen produced by a plant fertilizes the egg produced by a different plant. This increases genetic diversity in offsprings. In case of self-fertilization , the pollen produced by the plant fertilizes the egg produced by the same plant. This maintains or may decrease the genetic diversity in offsprings.

Question 4

Explain the technical differences between a cross-fertilization experiment versus a self-fertilization experiment.

Question 5

Describe the difference between genotype and phenotype. Give three examples. Is it possible for two individuals to have the same phenotype but different genotypes

Question 6

How long did it take Mendel to complete the experiment in Figure 2.5
FIGURE 2.5 Mendel's analysis of single-factor crosses.
Starting material: Mendel began his experiments with true-breeding strains of pea plants that varied in only one of seven different characters (see Figure 2.4).
FIGURE 2.4 An illustration of the seven characters that Mendel studied. Each character was found as two variants that were decisively different from each other.

Question 7

With regard to genotypes, what is a true-breeding organism

Question 8

For all seven characters described in the data of Figure 2.5, Mendel allowed the F 2 plants to self-fertilize. He found that when F 2 plants with recessive traits were crossed to each other, they always bred true. However, when F 2 plants with dominant traits were crossed, some bred true but others did not. A summary of Mendel's results is shown here.
The Ratio of True-Breeding and Non-True-Breeding Parents of the F 2 Generation
When considering the data in this table, keep in mind that it describes the characteristics of the F 2 generation parents that had displayed a dominant phenotype. These data were deduced by analyzing the outcome of the F 3 generation. Based on Mendel's laws, explain the 1:2 ratio obtained in these data.
FIGURE 2.5 Mendel's analysis of single-factor crosses.
Starting material: Mendel began his experiments with true-breeding strains of pea plants that varied in only one of seven different characters (see Figure 2.4).
FIGURE 2.4 An illustration of the seven characters that Mendel studied. Each character was found as two variants that were decisively different from each other.

Question 9

How can you determine whether an organism is heterozygous or homozygous for a dominant trait

Question 10

From the point of view of crosses and data collection, what are the experimental differences between a monohybrid and a dihybrid experiment

Question 11

In your own words, describe Mendel's law of segregation. Do not use the word "segregation" in your answer.

Question 12

As in many animals, albino coat color is a recessive trait in guinea pigs. Researchers removed the ovaries from an albino female guinea pig and then transplanted ovaries from a true-breeding black guinea pig. They then mated this albino female (with the transplanted ovaries) to an albino male. The albino female produced three offspring. What were their coat colors Explain the results.

Question 13

Based on genes in pea plants that we have considered in this chapter, which statement(s) is/are not correct
A. The gene causing tall plants is an allele of the gene causing dwarf plants.
B. The gene causing tall plants is an allele of the gene causing purple flowers.
C. The alleles causing tall plants and purple flowers are dominant.

Question 14

The fungus Melampsora lini causes a disease known as flax rust. Different strains of M. lini cause varying degrees of the rust disease. Conversely, different strains of flax are resistant or sensitive to the various varieties of rust. The Bombay variety of flax is resistant to M. lini -strain 22 but sensitive to M. lini -strain 24. A strain of flax called 770B is just the opposite; it is resistant to strain 24 but sensitive to strain 22. When 770B was crossed to Bombay, all F 1 individuals were resistant to both strain 22 and strain 24. When F 1 individuals were self-fertilized, the following data were obtained:
43 resistant to strain 22 but sensitive to strain 24
9 sensitive to strain 22 and strain 24
32 sensitive to strain 22 but resistant to strain 24
110 resistant to strain 22 and strain 24
Explain the inheritance pattern for flax resistance and sensitivity to M. lini strains.

Question 15

In a cross between a heterozygous tall pea plant and a dwarf plant, predict the ratios of the offspring's genotypes and phenotypes.

Question 16

For Mendel's data shown in Figure 2.8, conduct a chi square analysis to determine if the data agree with Mendel's law of independent assortment.
FIGURE 2.8 Mendel's analysis of two-factor crosses.
Starting material: In this experiment, Mendel began with two types of true-breeding strains of pea plants that were different with regard to two characters. One strain produced round, yellow seeds ( RRYY ); the other strain produced wrinkled, green seeds ( rryy ).

Question 17

Do you know the genotype of an individual with a recessive trait and/or a dominant trait Explain your answer.

Question 18

Would it be possible to deduce the law of independent assortment from a monohybrid experiment Explain your answer.

Question 19

A cross is made between a pea plant that has constricted pods (a recessive trait; smooth is dominant) and is heterozygous for seed color (yellow is dominant to green) and a plant that is heterozygous for both pod texture and seed color. Construct a Punnett square that depicts this cross. What are the predicted outcomes of genotypes and phenotypes of the offspring

Question 20

In fruit flies, curved wings are recessive to straight wings, and ebony body is recessive to gray body. A cross was made between true-breeding flies with curved wings and gray bodies to flies with straight wings and ebony bodies. The F 1 offspring were then mated to flies with curved wings and ebony bodies to produce an F 2 generation.
A. Diagram the genotypes of this cross, starting with the parental generation and ending with the F 2 generation.
B. What are the predicted phenotypic ratios of the F 2 generation
C. Let's suppose the following data were obtained for the F 2 generation:
114 curved wings, ebony body
105 curved wings, gray body
111 straight wings, gray body
114 straight wings, ebony body
Conduct a chi square analysis to determine if the experimental data are consistent with the expected outcome based on Mendel's laws.

Question 21

A pea plant that is heterozygous with regard to seed color (yellow is dominant to green) is allowed to self-fertilize. What are the predicted outcomes of genotypes and phenotypes of the offspring

Question 22

A recessive allele in mice results in an abnormally long neck. Sometimes, during early embryonic development, the abnormal neck causes the embryo to die. An experimenter began with a population of true-breeding normal mice and true-breeding mice with long necks. Crosses were made between these two populations to produce an F 1 generation of mice with normal necks. The F 1 mice were then mated to each other to obtain an F 2 generation. For the mice that were born alive, the following data were obtained:
522 mice with normal necks
62 mice with long necks
What percentage of homozygous mice (that would have had long necks if they had survived) died during embryonic development

Question 23

Describe the significance of nonparentals with regard to the law of independent assortment. In other words, explain how the appearance of nonparentals refutes a linkage hypothesis.

Question 24

The data in Figure 2.5 show the results of the F 2 generation for seven of Mendel's crosses. Conduct a chi square analysis to determine if these data are consistent with the law of segregation.
FIGURE 2.5 Mendel's analysis of single-factor crosses.
Starting material: Mendel began his experiments with true-breeding strains of pea plants that varied in only one of seven different characters (see Figure 2.4).
FIGURE 2.4 An illustration of the seven characters that Mendel studied. Each character was found as two variants that were decisively different from each other.

Question 25

For the following pedigrees, describe what you think is the most likely inheritance pattern (dominant versus recessive). Explain your reasoning. Filled (black) symbols indicate affected individuals.
(a)
(b)

Question 26

Let's suppose you conducted an experiment involving genetic crosses and calculated a chi square value of 1.005. There were four categories of offspring (i.e., the degrees of freedom equaled 3). Explain what the 1.005 value means. Your answer should include the phrase "80% of the time."

Question 27

Ectrodactyly, also known as "lobster claw syndrome," is a recessive disorder in humans. If a phenotypically unaffected couple produces an affected offspring, what are the following probabilities
A. Both parents are heterozygotes.
B. An offspring is a heterozygote.
C. The next three offspring will be phenotypically unaffected.
D. Any two out of the next three offspring will be phenotypically unaffected.

Question 28

A tall pea plant with axial flowers was crossed to a dwarf plant with terminal flowers. Tall plants and axial flowers are dominant traits. The following offspring were obtained: 27 tall, axial flowers; 23 tall, terminal flowers; 28 dwarf, axial flowers; and 25 dwarf, terminal flowers. What are the genotypes of the parents

Question 29

Identical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate sperm and separate egg cells. If two parents with brown eyes (a dominant trait) produce one twin boy with blue eyes, what are the following probabilities
A. If the other twin is identical, he will have blue eyes.
B. If the other twin is fraternal, he or she will have blue eyes.
C. If the other twin is fraternal, he or she will transmit the blue eye allele to his or her offspring.
D. The parents are both heterozygotes.

Question 30

A cross was made between two strains of plants that are agriculturally important. One strain was disease-resistant but herbicide-sensitive; the other strain was disease-sensitive but herbicide-resistant. A plant breeder crossed the two plants and then allowed the F 1 generation to self-fertilize. The following data were obtained:
Formulate a hypothesis that you think is consistent with the observed data. Test the goodness of fit between the data and your hypothesis using a chi square test. Explain what the chi square results mean.

Question 31

In cocker spaniels, solid coat color is dominant over spotted coat color. If two heterozygous dogs were crossed to each other, what would be the probability of the following combinations of offspring
A. A litter of five pups, four with solid fur and one with spotted fur.
B. A first litter of six pups, four with solid fur and two with spotted fur, and then a second litter of five pups, all with solid fur.
C. A first litter of five pups, the firstborn with solid fur, and then among the next four, three with solid fur and one with spotted fur, and then a second litter of seven pups in which the firstborn is spotted, the second born is spotted, and the remaining five are composed of four solid and one spotted animal.
D. A litter of six pups, the firstborn with solid fur, the second born spotted, and among the remaining four pups, two with spotted fur and two with solid fur.

Question 32

A cross was made between a plant that has blue flowers and purple seeds to a plant with white flowers and green seeds. The following data were obtained:
Start with the hypothesis that blue flowers and purple seeds are dominant traits and that the two genes assort independently. Calculate a chi square value. What does this value mean with regard to your hypothesis If you decide to reject your hypothesis, which aspect of the hypothesis do you think is incorrect (i.e., the idea that blue flowers and purple seeds are dominant traits, or the idea that the two genes assort independently)

Question 33

A cross was made between a white male dog and two different black females. The first female gave birth to eight black pups, and the second female gave birth to four white and three black pups. What are the likely genotypes of the male parent and the two female parents Explain whether you are uncertain about any of the genotypes.

Question 34

In humans, the allele for brown eye color ( B ) is dominant to blue eye color ( b ). If two heterozygous parents produce children, what are the following probabilities
A. The first two children have blue eyes.
B. A total of four children, two with blue eyes and the other two with brown eyes.
C. The first child has blue eyes, and the next two have brown eyes.

Question 35

Albinism, a condition characterized by a partial or total lack of skin pigment, is a recessive human trait. If a phenotypically unaffected couple produce an albino child, what is the probability that their next child will be albino

Question 36

A true-breeding tall plant was crossed to a dwarf plant. Tallness is a dominant trait. The F 1 individuals were allowed to self-fertilize. What are the following probabilities for the F 2 generation
A. The first plant is dwarf.
B. The first plant is dwarf or tall.
C. The first three plants are tall.
D. For any seven plants, three are tall and four are dwarf.
E. The first plant is tall, and then among the next four, two are tall and the other two are dwarf.

Question 37

For pea plants with the following genotypes, list the possible gametes that the plant can make:
A. TT Yy Rr
B. Tt YY rr
C. Tt Yy Rr
D. tt Yy rr

Question 38

An individual has the genotype Aa Bb Cc and makes an abnormal gamete with the genotype AaBc. Does this gamete violate the law of independent assortment or the law of segregation (or both) Explain your answer.

Question 39

In people with maple syrup urine disease, the body is unable to metabolize the amino acids leucine, isoleucine, and valine. One of the symptoms is that the urine smells like maple syrup. An unaffected couple produced six children in the following order: unaffected daughter, affected daughter, unaffected son, unaffected son, affected son, and unaffected son. The youngest unaffected son marries an unaffected woman and has three children in the following order: affected daughter, unaffected daughter, and unaffected son. Draw a pedigree that describes this family. What type of inheritance (dominant or recessive) would you propose to explain maple syrup urine disease

Question 40

Marfan syndrome is a rare inherited human disorder characterized by unusually long limbs and digits plus defects in the heart (especially the aorta) and the eyes, among other symptoms. Following is a pedigree for this disorder. Affected individuals are shown with filled (black) symbols. What type of inheritance pattern do you think is the most likely

Question 41

A true-breeding pea plant with round and green seeds was crossed to a true-breeding plant with wrinkled and yellow seeds. Round and yellow seeds are the dominant traits. The F 1 plants were allowed to self-fertilize. What are the following probabilities for the F 2 generation
A. An F 2 plant with wrinkled, yellow seeds.
B. Three out of three F 2 plants with round, yellow seeds.
C. Five F 2 plants in the following order: two have round, yellow seeds; one has round, green seeds; and two have wrinkled, green seeds.
D. An F 2 plant will not have round, yellow seeds.

Question 42

A true-breeding tall pea plant was crossed to a true-breeding dwarf plant. What is the probability that an F 1 individual will be true-breeding What is the probability that an F 1 individual will be a true-breeding tall plant

Question 43

What are the expected phenotypic ratios from the following cross: Tt Rr yy Aa × Tt rr YY Aa , where T = tall, t = dwarf, R = round, r = wrinkled, Y = yellow, y = green, A = axial, a = terminal; T , R , Y , and A are dominant alleles. Note: See solved problem S3 for help in answering this problem.
Solved Problem S3
A pea plant is heterozygous for three genes ( Tt Rr Yy ), where T = tall, t = dwarf, R = round seeds, r = wrinkled seeds, Y = yellow seeds, and y = green seeds. If this plant is self-fertilized, what are the predicted phenotypes of the offspring, and what fraction of the offspring will occur in each category

Question 44

When an abnormal organism contains three copies of a gene (instead of the normal number of two copies), the alleles for the gene usually segregate so that a gamete will contain one or two copies of the gene. Let's suppose that an abnormal pea plant has three copies of the height gene. Its genotype is TTt. The plant is also heterozygous for the seed color gene, Yy. How many types of gametes can this plant make, and in what proportions (Assume that it is equally likely that a gamete will contain one or two copies of the height gene.)

Question 45

Honeybees are unusual in that male bees (drones) have only one copy of each gene, but female bees have two copies of their genes. That is because drones develop from eggs that have not been fertilized by sperm cells. In bees, the trait of long wings is dominant over short wings, and the trait of black eyes is dominant over white eyes. If a drone with short wings and black eyes was mated to a queen bee that is heterozygous for both genes, what are the predicted genotypes and phenotypes of male and female offspring What are the phenotypic ratios if we assume an equal number of male and female offspring

Question 46

A pea plant that is dwarf with green, wrinkled seeds was crossed to a true-breeding plant that is tall with yellow, round seeds. The F 1 generation was allowed to self-fertilize. What types of gametes, and in what proportions, would the F 1 generation make What would be the ratios of genotypes and phenotypes of the F 2 generation

Question 47

A true-breeding plant with round and green seeds was crossed to a true-breeding plant with wrinkled and yellow seeds. The F 1 plants were allowed to self-fertilize. What is the probability of obtaining the following plants in the F 2 generation: two that have round, yellow seeds; one with round, green seeds; and two with wrinkled, green seeds

Question 48

Wooly hair is a rare dominant trait found in people of Scandinavian descent in which the hair resembles the wool of a sheep. A male with wooly hair, who has a mother with straight hair, moves to an island that is inhabited by people who are not of Scandinavian descent. Assuming that no other Scandinavians immigrate to the island, what is the probability that a great-grandchild of this male will have wooly hair (Hint: You may want to draw a pedigree to help you figure this out.) If this wooly-haired male has eight great-grandchildren, what is the probability that one out of eight will have wooly hair

Question 49

Huntington disease is a rare dominant trait that causes neuro-degeneration later in life. A man in his thirties, who already has three children, discovers that his mother has Huntington disease though his father is unaffected. What are the following probabilities
A. That the man in his thirties will develop Huntington disease.
B. That his first child will develop Huntington disease.
C. That one out of three of his children will develop Huntington disease.

Question 50

A woman with achondroplasia (a dominant form of dwarfism) and a phenotypically unaffected man have seven children, all of whom have achondroplasia. What is the probability of producing such a family if this woman is a heterozygote What is the probability that the woman is a heterozygote if her eighth child does not have this disorder