Genetics: Chapter 2
Jane and John are considering having another child. Given the pedigree you constructed and the mode of inheritance for galactosemia, what is the risk that their next child will have the disorder?
1/4 (because they are both heterozygotes)
If Patricia and Les have another child, what is the probability that they will have a daughter that is affected with galactosemia? Express your answer as a fraction (example 3/5).
1/8
If flies that are heterozygous for all three traits are crossed with flies that are homozygous recessive for all three traits, what proportion of the offspring would you expect to be heterozygous for all three traits? Express your answer as a fraction (example: 3/5).
1/8
In Drosophila, straight wings are dominant to curved wings (c), smooth eyes are dominant to sparkling eyes (spa), and tan body is dominant to ebony body color (e). If flies that are heterozygous for all three traits are crossed, what proportion of the offspring would you expect to be heterozygous for all three traits? Express your answer as a fraction (example: 3/5).
1/8
What is the probability that the first child of Amanda and Brice will have galactosemia?
1/9
If this is an autosomal recessive disorder, what is the probability that individual II-3 is a heterozygous carrier of the disorder? Express your answer as a fraction (example: 3/5).
2/3
What is the probability that Amanda is a carrier of the allele for galactosemia?
2/3
What is the probability that Brice is a carrier?
2/3
If the first three F2 offspring grown from the cross described above are round, what is the probability that the next F2 offspring will be wrinkled?
25%
Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?
3 round seeds, 1 wrinkled seed
If flies that are heterozygous for all three traits are crossed, what proportion of the offspring would you expect to have straight wings, sparkling eyes, and tan bodies? Express your answer as a fraction (example: 3/5).
9/64
Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions. Identify the genotype of each person (except Amanda and Brice), using GG and gg to represent the dominant and recessive alleles, respectively. Drag the labels to their respective targets. Not all labels will be used.
Amanda's family: Dad = Gg Mom = Gg Brother = gg Brice's family: Dad = Gg Mom = Gg Sister = gg
Look over the pedigree you constructed in Part A. Based on the inheritance pattern, which mode of inheritance must be the cause of galactosemia?
Autosomal recessive
Which of the following is a possible mechanism of inheritance for the disorder presented in the pedigree?
Autosomal recessive and X-linked recessive
Which term describes the individual in a pedigree whose phenotype was first brought to the attention of a medical researcher?
Proband
Progeny that are expected to have the genotype AABBCcddE−AABBCcddE−. Express your answer using three decimal places.
0.006
An organism having the genotype AaBbCcDdEeAaBbCcDdEe is self-fertilized. Assuming the five genes assort independently, determine the following proportions. Gametes that are expected to carry only recessive alleles. Express your answer using three decimal places.
0.031
Gametes that are expected to be ABcDeABcDe . Express your answer using three decimal places.
0.031
Progeny that are expected to have a genotype identical to that of the parent. Express your answer using three decimal places.
0.031
Progeny that are expected to have a phenotype identical to that of the parent. Express your answer using three decimal places.
0.237
A pea plant is heterozygous for two genes; one controlling height, one controlling color. The genotype is written PpTt. Based on the Law of Independent Assortment, approximately what proportion of the pollen produced by this plant should have the genotype PT?
1/4
If the first child has galactosemia, what is the probability that the second child will have galactosemia?
1/4
The pedigree from Part C is shown below. Individuals III-3 and III-4 are expecting their first child when they become aware that they both have a family history of this recessive condition. As their genetic counselor, you can calculate the probability that they are carriers and that their child will be affected with the condition. Complete each statement by dragging the correct label to the appropriate location. Labels can be used once, more than once, or not at all.
1. The probability that III-3 is a carrier (Rr) = 2/3 2. The probability that III-4 is a carrier (Rr) = 1/2 3. The probability that IV-1 will be affected (rr) = 1/12
What is the probability that Mary and Justin will have an affected child? Express your answer as a fraction (example 3/5).
1/18
The 9:3:3:1 ratio exhibited in the F2 generation of a dihybrid cross is a genotypic ratio.
False
The larger the number of total individual counts in a chi-square test, the higher the degrees of freedom (df).
False
Pedigree 3 from Part A is shown below. Recall that this pedigree shows the inheritance of a rare, autosomal recessive condition.Note: Individual II-3 is homozygous for the wild-type allele; she has no family history of the rare condition. Fill in the genotypes for the indicated individuals in the pedigree by dragging the best label to the appropriate location. Labels can be used once, more than once, or not at all.
I-1 = rr II-1 = Rr; 11-4 = Rr III-2 = R_; III-3 = R_; III-4 = R_
Pedigree 2 from Part A is shown below. Recall that this pedigree shows the inheritance of a rare, autosomal dominant condition. Fill in the genotypes for the indicated individuals in the pedigree by dragging the best label to the appropriate location. Labels can be used once, more than once, or not at all.
I-4 = Dd II-1 = Dd; II-2 = dd; II-4 = Dd III-2 = dd; III-3 = Dd; III-4 = dd
If this is an autosomal recessive disorder, of the following individuals, which is NOT an obligate carrier?
III-6
Which of the following would be true of a plant heterozygous for a single gene controlling flower color? (Assume complete dominance).
If crossed with another heterozygous plant, the majority of progeny will have the dominant flower color
Which of the following statements about autosomal recessive traits is true?
If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait
The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true?
The value of observed - expected for this cell = -2
Which of the following statements is true regarding individual III-5?
Individual III-5 is male Individual III-5 is affected by the genetic condition Individual III-5 is the proband
Galactosemia is a condition that affects how the body digests the sugar galactose. The most common form of galactosemia, type I, is the most severe, and it results from mutations within the GALT gene, which encodes for an enzyme that processes galactose. Galactosemia is inherited in an autosomal recessive pattern.Imagine that your friend Mary has normal metabolism, but that her brother John has galactosemia. Mary and John's parents, Patricia and Les, are unaffected, although their maternal grandmother, Jean, also had the condition. If wild-type GALT is designated as G and the recessive allele is designated as g, determine the genotypes of the following individuals. Drag a genotype to each individual in the pedigree. Labels may be used more than once or not at all.
Jean = gg Patricia = Gg Les = Gg John = gg Mary = G_
Mary marries an unaffected man, Justin, whose paternal uncle has galactosemia. Determine the genotypes for Justin's family. Drag a genotype to each individual in the pedigree. Labels may be used more than once or not at all.
Justin's family: Grandpa = Gg Grandma = Gg Dad = G_ Uncle = gg Justin = G_
Galactosemia is a human genetic disorder caused by a deficiency of the enzyme galactose-1-phosphate uridylyltransferase (commonly called GALT). Children with galactosemia seem normal at birth, but begin to show symptoms as soon as they drink milk. This is because they cannot metabolize galactose, a simple sugar that results from the breakdown of lactose (the sugar found in milk). Early symptoms of galactosemia include vomiting and diarrhea. If untreated, affected babies will develop enlarged livers, cataracts, and mental retardation. Depending on the alleles the baby has inherited, early death may result. John and Jane Jones' newborn baby girl, Leah, has just been diagnosed with galactosemia. Prior to their genetic counseling appointment, they submitted this family history: John and Jane's older child, a son named Lee, does not have galactosemia. John is the only child of Hanna and Harry. Harry was an only child. Hanna has two older sisters, Hope (the oldest) and Holly. Both Harry and Hanna's parents lived in good health into their 80s. Jane's brother, Joe, is married to Jen. They have a son, Les, who is a healthy nine-year-old with myopia (nearsightedness) but no sign of galactosemia. Jane's mother, Hilda, is alive and healthy; Jane's father, Henry, passed away last year of a sudden heart attack. Hilda and Henry have no family history of galactosemia. Use the information in the family history to construct a pedigree for this family. Drag the correct symbols to their appropriate locations on the pedigree below. Not all symbols will be used.Hann
N/A Lines by order: First line = Hanna's father - Harry's father Second line = Hilda - Hope - Holly - Hanna - Harry Third line = Jen - Joe - Jane - John Fourth line = Les - Lee - Leah Only Leah is diagnosed with galactosemia
If Jane and John want to have another child, they plan to see a genetic counselor to find out when it would be best to test for galactosemia. A newborn with galactosemia must be put on a lactose- and galactose-free diet as soon as possible after birth. Even on this diet, affected individuals may still suffer from learning disabilities, ovarian failure (in young women), late-onset cataracts, and early death. Which of the following tests would be most useful for Jane and John to have?
Newborn screening (either assaying for the GALT enzyme or measuring excess galactose in the newborn's blood)
Of the methods listed below, which would be the best way to determine which of two alleles of a gene is dominant to the other?
Observe the relevant phenotype in the progeny that result from a cross between individuals from two different pure-breeding lines
Geneticists analyze pedigrees to follow the inheritance of genetically controlled conditions. Three things must be determined in a pedigree analysis: The mode of inheritance of the condition. In this tutorial, this means deciding if a condition is caused by an autosomal dominant or autosomal recessive allele. The genotypes of individuals in the pedigree (as far as can be known) based on their phenotype and the phenotypes of their parents or children. The probability that certain individuals will have the condition. This requires assigning probability values to some individuals whose genotypes cannot be determined with certainty. It also requires an understanding of how and when to apply the product and sum rules. The pedigrees below show the inheritance of three separate, rare autosomal conditions in different families. For each pedigree, decide if the condition is better explained as recessive or dominant. Drag the correct label to the appropriate location. Labels can be used once, more than once, or not at all.
Pedigree 1 = Autosomal recessive condition Pedigree 2 = Autosomal dominant condition Pedigree 3 = Autosomal recessive condition
What is the most likely mode of transmission for a trait that is not expressed in parents but is expressed by one half of the sons?
Rare X-linked recessive
You would like to know whether the progeny of a pair of mated fruit flies are distributed among the resulting four phenotypic classes in a 1:1:1:1 ratio. You perform a chi-square test and obtain a p value of 0.04. Assuming you have done the test correctly, select the best interpretation of this result.
The differences between the observed and expected counts are too large to be attributed to chance
Which of the following phenomena is a consequence of Independent Assortment?
The phenotypic ratio among phenotypes produced from an F1 X F1 dihybrid cross is 9:3:3:1
In an individual that is heterozygous for a particular trait, expression of the recessive allele is masked.
True
The 3:1 phenotypic ratio observed among progeny of an F1 X F1 cross requires random union of gametes.
True
One character in peas that Mendel studied was yellow versus green seeds. A cross between a homozygous yellow line (GG) and a homozygous green line (gg) will result in F1 plants that are heterozygous (Gg) for this trait and produce yellow seeds. When an F1 plant undergoes meiosis, what gamete types will it produce, and in what proportions? Use your understanding of Mendel's Law of Segregation to label each gamete possibility as "correct" or "incorrect."
a. 3/4 G 1/4 g = incorrect b. 1/2 G 1/2 g = correct c. 1/2 GG 1/2 gg = incorrect d. 1/2 Gg 1/2 Gg = incorrect e. 3/4 g 1/4 G = incorrect f. 1/2 g 1/2 g = incorrect
