name:______
student ID:______
Genetics L311 exam 2
October 13, 2017
Directions: Please read each question carefully. Answer questions as concisely as possible. Excessively long answers, particularly if they include any inaccuracies, may result in deduction of points. You may use the back of the pages as work sheets, but please write your answer in the space allotted. However, you must show all your work. Clearly define your genetic symbols. We will not make guesses as to what a particular symbol is intended to mean. Also, don’t assume that strains are true-breeding unless this is stated in the question. Finally, show all your work. Good luck.
page 2 ______(20 points possible)
page 3 ______(24 points possible)
page 4 ______(24 points possible)
page 5 ______(20 points possible)
page 6 (12 points possible)
total ______(of 100 points possible)
1. Short answers (2 points each, 20 points total)
A. A family of small, basic proteins that associate with DNA are called the histones. These are instrumental in forming nucleosomes.
B. Traits that are seen in both males and females but that are more severe in one gender than the other are said to be sex influenced.
C. Error-prone repair (or SOS repair) is a DNA repair pathway that can be induced in the presence of extensive DNA damage. It often results in the introduction of the incorrect nucleotides, thereby frequently producing mutations.
D. Suppression occurs when mutation in one gene reverses the effect of mutation in a second gene (i.e. restores the phenotype to wild type).
E. A change in DNA that leads to a different codon that encodes the same amino acid as was originally found in the protein is referred to as a silent or synonymous mutation.
F. A(n) carcinogen is an environmental agent that increases the risk of developing cancer.
G. Crossing over that occurs between two genes in a cell heterozygous for those genes, leading to a new combination of alleles, produces recombination.
For the following, please provide a brief definition of the term given:
H. null mutation: This is a mutation that completely eliminates gene function.
I. holocentric chromosome: This is a chromosome in which the centromere can form along the entire length of the chromosome.
J. genetic anticipation: This is the phenomenon where some genetic disorders tend to worsen in subsequent generations. It is produced by expansion of trinucleotide repeats, which following an initial expansion are prone to further expansion.
2. The hypothetical three-eyed cicada has been found in several true breeding strains. One has blue wings and long antennae. The second has red eyes. You cross blue-winged, long antennaed X red eyed and find the progeny all have all wild type phenotypes (i.e. not blue winged, long antennaed or red eyed). You test cross the F1’s and find the results shown below. Recessive phenotypes are listed below
123 long antenna, blue wing, red eyed
4513 long antenna, blue wing
118 blue wing, red eyed
19 long antenna, red eyed
125 long antenna
4781 red eyed
21 blue wing
134 wild type
9834
A. Please calculate the genetic distance between all of the linked genes, if any are linked. If not linked please describe how you reached that conclusion. Please show your work (12 points).
b – l: (118 + 125 + 19 + 21)/9834 X 100 = 2.9 cM
l – r: (123 + 134 + 19 + 21)/9834 X 100 = 3.0 cM
b – r: 2.9 + 3.0 = 5.9 cM
3. You find a rare shorebird, J. hainae, living in the sand dunes of Northern Indiana. This species normally has gray spots but some individuals have white spots. You cross the following true breeding strains together and get these results:
Cross 1: Gray spot male X white spot female à all offspring have white spots
Cross 2: Gray spot female X white spot male à all offspring have gray spots
Cross 3: White spotted males from cross 1 X gray spotted females from cross 2 à 1/2 gray and 1/2 white
A. What mode of inheritance explains these results (4 points)?
This looks like paternal genomic imprinting
B. If a bird inherited a nonsense mutation that knocked out gene function of the paternal copy of the gene and inherited wild type from mom, what phenotype would the offspring show (4 points)?
Wild type or gray spots
C. If a bird inherited a nonsense mutation that knocked out gene function of the maternal copy of the gene and inherited wild type from dad, what phenotype would the offspring show (4 points)?
Mutant or white spots
4. While hiking the Bornean jungle you find two true breeding strains of the common jungle katydid, Z. crabtreeae. Strain 1 has green wing covers and short hind legs and strain 2 has gray wing covers and long hind legs. Note that green and short are recessive. A cross of strain 1 X strain 2 produces double heterozygotes, which are crossed to yield the following:
A. You wonder if the two genes responsible for these traits are linked. Please calculate chi square for this cross. What is the probability that the genes are linked? What do you conclude (10 points).
Chi2 = (1042 – 1010)2/1010 + (978 – 1010)2/1010
= 1.01 + 1.01 = 2.02
The probability that the genes are unlinked is roughly 0.2 (somewhere between 0.1 and 0.5 anyway) so the probability that they are linked is roughly 0.8 (between 0.5 and 0.9). We cannot conclude linkage.
5. While net fishing near lake Monroe you catch several individuals of the elusive twelve-spined stickleback fish, C. drakeae. Some of your fish have a large red blotch on their belly whereas others have a yellow blotch. These traits breed true in the original strains. To understand the genetics that underlie this trait, you cross orange-bellied fish X yellow-bellied fish. The offspring all have orange bellies. You cross the orange-bellied F1’s amongst themselves and find the results below:
385 orange belly O-Y-
131 red belly O-yy
173 yellow belly ooY- and ooyy
A. Please provide the genotypes of the F2’s above (9 points).
B. You cross orange-bellied F2 X original, i.e. true breeding, yellow bellied fish. What fraction of the offspring will have red bellies (5 points)?
O-Y- X ooyy 2/9(1/2) + 4/9(1/4) = 2/9
1/9 OOYY X ooyy => OoYy
2/9 OoYY X ooyy => OoYy and ooYy
2/9 OOYy X ooyy => OoYy and Ooyy
4/9 OoYy X ooyy => OoYy, ooYy, Ooyy, ooyy
6. In your studies of the rare Rao’s field mouse you discover two discreet strains, one with tan, long fur and a second with gray, short fur. In the lab you show that the two traits are produced by two alleles each of two different genes and that those genes, g (which produces gray fur when wild type) and s (which produces long fur when wild type) both reside on chromosome 3. In the course of your studies you had crossed numerous tan, long furred animals with gray, short furred animals. All the offspring had gray, long fur except for one unusual individual that had gray, long fur everywhere except for a patch of tan, long fur near a patch of gray, short fur. Please diagram (include the genes) and name the process that could have produced the cells of these two patches (10 points).
Mitotic recombination
7. When traveling in a cave near Bloomington, you came across a species of bat, G. baileyae. Two recessive mutations are known, one causing glow-in-the-dark wings (g) and the other causing hairy feet (h). Because you wish to create a truly frightening animal, you cross heterozygous parents, both with the mutations in trans, hoping to produce bats with hairy feet and glowing wings. Since the mutations are only 4 mu apart you assume no double crossovers.
A. What are the genotypes of the parents (4 points)?
g+ h–/g– h+ X same
B. What percentage of offspring will have the same genotype as their parents (6 points)?
g+ h–/g– h+ X g+ h–/g– h+
each will produce 96% parental (g– h+ and g– h+) and 4% recombinant. To produce the same genotype as parent requires g– h+ from the first and g+ h– from the second or vice versa. Answer is 0.48(0.48) + 0.48(0.48) = 0.46
8. The giant west coast banana slug grows 5 – 6 inches long and is normally found in shades of yellow or brown. Suppose you have identified the gene that controls pigmentation in banana slugs. The wild-type sequence includes the sequence: ATG TCT TGT TGT ATT GGG GTG
Met Ser Cys Cys Ile Gly Val
You sequence the gene from several strains and find the results given below. In each case please name the type of mutation, give the sequence of the resulting protein and give an example of a mutagen other than ionizing radiation that is likely to produce the change listed. An asterisk indicates the approximate location of the mutation. Do not use the same mutagen more than once (4 points each).
A. ATG TCT TAT TGT ATT GGG GTG
Protein: Met Ser Tyr Cys Ile Gly Val
Name of mutation: transition or missense
Mutagen: EMS
B. GTG TCT TGT TGT ATT GGG GTG
Protein: Val Ser Cys Cys Ile Gly Val
Name of mutation: transition or missense
Mutagen: 5BU or 2AP
C. ATG TCT TTG TTG TAT TGG GGT G
Protein: Met Ser Leu Leu Tyr Trp Gly
Name of mutation: frameshift
Mutagen: acridine orange
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