BSCI 106 MIDTERM I
Name ____________________25 February 2000 SS # _____________________
Drs. Thorne & Hawthorne T.A. Name ________________
100 total points Lab Section _______________
__False_ 1. The enlarged, serrated canines on sabertooth cats are an example of a vestigial trait.
__False_ 2. The fact that cheetahs are apparently universal donors and recipients of successful skin grafts within their species is evidence that the populations have undergone directional selection.
__False_ 3. If a drought indiscriminantly causes death of 90% of a population, there would be natural selection.
__True__ 4. Frameshift mutations that occur early in a gene’s nucleotide sequence are normally less viable than frameshift mutations that occur later in the sequence.
__False_ 5. Independent assortment produces new combinations of genes along the same chromosome.
__True__ 6. A walrus cell with the genotype Tt Bb (T = long tusks; t = normal tusks; B = bulging (False also blubber, b = svelt physique) undergoes meiosis. Assuming no recombination, the accepted due daughter cells of that one meiotic division will have 2 different genotypes.
to ambiguity)
7. Homologous traits are:
8. During industrialization in England,
9. Mendel’s Law of Independent Assortment refers to assortment between which of the following structures? a. sister chromatids (copies of a chromosome)
b. homologous chromosomes
c. nonhomologous chromosomes
d. linked genes
e. zygotes
10. In cocker spaniels, black color is due to a dominant gene B and red color to its recessive allele b. Solid color is dependent on a dominant gene S and white spotting on its recessive allele s. A solid red male was mated to a black and white female. They had five puppies: one solid black, one solid red, one black and white, and two red and white. What were the genotypes of the parents?
11. Selection acts on _________________; however evolution depends on _________________.
12. Which of the following individuals has the greatest fitness:
13
. List four conditions that must be met for there to be no change in allele or genotype frequencies from generation to generation:no migration
14. List the four requirements for Darwinian evolution:
15
. Give an example of how your inclusive fitness can be increased.
if a close relative has a child
16. What is directional selection?
one extreme of a phenotype distribution is favored — results in the frequency distribution peak shifting in one direction
17. How might Lamarck have explained the presence of webbed feet on aquatic birds?
swimming birds stretched their claws as they swam, and that stretched webbing was passed on to the next generation (theory of acquired characteristics)
18. A right-handed (dominant allele) woman who had one left-handed (recessive) parent marries a left-handed man. What is the probability that both of their first two children will be left handed?
___1/4____
19. There are a number of debilitating or lethal human diseases in which symptoms do not appear until the affected individual is 35 or older. Some of these "late onset" diseases are caused by dominant alleles, yet whether dominant or recessive the frequency of these alleles may remain stable in the population, or even increase. Assuming no superiority of heterozygotes, why are such deleterious genes not selected out by natural selection?
the debilitating or lethal phenotype expressed by late onset diseases does not appear until an affected individual has already reproduced, and therefore passed those genes on to the next generation
Please keep your answers above this line.
Genetics Problems: answer each of the next 5 questions (no choice)
:20. (20 points) Questions a — f below refer to the following original cell:
a. (3 points) What is the haploid number of this cell? _____4
b. (2 points) List all of the alleles indicated in the cell, separated by commas: ____________________________________ A, a, B, b, E, e, R, r
c. (3 points) These alleles represent how many loci? _____ 4
d. (2 points) Draw any 2 homologous chromosomes shown in the figure, in the same stage of cell division as shown in the figure, each clearly labelled with its allele.
e. (2 points) How many genetic combinations might appear in gametes produced from cells of the illustrated cell’s genotype, due to segregation alone (i.e. assume no recombination)? ______ 2n = 24 = 16
f. (8 points) Draw an arrangement of the duplicated chromosomes during the metaphase I stage of meiosis, and then follow that meiotic division to illustrate metaphase II. Label the positions of ALL alleles, even on duplicated chromosomes. Assume no recombination. Take time to make your drawing completely clear; ambiguities will be marked as incorrect.
Example of Metaphase I in Meiosis:
Follow your Metaphase I division above, and illustrate the configuration(s) at Metaphase II:
21. (6 points) You discover that your pet guinea pig has 6 toes on each foot. This trait, called polydactyly, is coded for by a dominant allele at a single locus. How would you determine whether your guinea pig was heterozygous for this condition? Make your answer clear and concise, outlining a specific protocol and how you would interpret results.
Test cross to a homozygous recessive individual.
Mate the 6-toed guinea pig (PP or Pp) to a normal mate, known to be pp. If the progeny are all 6-toed, the individual in question was PP. If approximately half of the offspring are normal, then the individual in question was Pp.
22. (6 pts) Hemophilia is inherited as an X-linked recessive trait. An apparently normal woman marries a normal man, but they are concerned about the risks of having children with the disease because the woman’s father was a hemophiliac. You are a genetic counselor, and the couple asks you to draw their geneology and to calculate answers to the questions below.
GENEOLOGY: [use conventional symbols; give the couple 4 hypothetical children (2 boys and 2 girls) whose genotypes reflect expected proportions]
What is the probabiity that a son will have hemophilia? _________ 1/2
What is the probabiity that a daughter will have hemophilia? __________ 0
What is the probabiity that a daughter will be carriers? _________ 1/2
23. (6 points) A parrot breeder bred parrots that were each heterozygous for 3 unlinked traits:
- crimson vs yellow feathers (crimson "C" is dominant to yellow "c")
What fraction of the offspring are expected to have crimson feathers, beady eyes, and dull claws?
Answer: _________________________________________________________________
(also give final equation if you solve the problem using probabilities)
_ x _ x _ = 9/64
24. (6 points) A population of 1,000 starfish lives on an island off the coast of California. These starfish are either rust colored (controlled by the dominant allele R) or tan (r). Dr. Dingbat discovers that this population is in Hardy-Weinberg equilibrium, that the starfish color is not sex-linked, and that the frequency of the r allele is 0.1.
What would be the expected allele, genotype, and phenotype frequencies of this population after 72 generations of Hardy-Weinberg equilibrium?
ALLELE FREQUENCIES: frequency r = .1
R = .9
GENOTYPE FREQUENCIES: RR = (.9)2 = .81
Rr = 2 (.9) (.1) = .18
rr = (.1)2 = .01
PHENOTYPE FREQUENCIES: Rust = 99%
Tan = 1%
Short Essay. Answer ONE of the following 2 questions. Make your answer complete, specific, and clear to read. If you answer more than 1, we will grade only the first. 6 points.
-
The answer needs to include 3 items:
1] must have variation in relevant phenotype (e.g. different cues to induce hibernation / migration, or different responses to those cues)
2] phenotypic variation must have fitness consequences (e.g. increases survivorship or reproduction if animal leaves before harsh winter weather sets in)
3] phenotypic variation must have a genetic basis
26. Why might new recessive mutations spread more slowly than dominant mutations in a population even if both the recessive and dominant mutations in question are beneficial?
Recessive mutations will initially be in a heterozygous genotype much more commonly than as homozygotes
Phenotype of the new mutation will not be expressed when it is a recessive mutant in a heterozygote. Natural selection acts on the phenotype, so the frequency of the new mutation does not change except when it is a homozygote
Dominant mutations will also initially be more frequently in a heterozygote than a homozygote, but the phenotype of the new dominant mutation will be expressed in heterozygotes. Selection can therefore act to increase the frequency of those new beneficial mutations.
BONUS QUESTIONS: You may choose to do ONE of these for 3 extra credit points. No partial credit will be given. To receive extra credit, you must have a complete, fully correct answer.
A. Reg and Tara each have a sibling with sickle cell disease. Neither Reg, Tara, nor any of their parents has the disease, and none of them has been tested to reveal whether or not they carry the sickle cell allele. Based on this information, calculate the probability that if this couple has a child, that child will have sickle cell disease.
2/3 x 2/3 x 1/4 = 4/36 = 1/9
B. Explain precisely how the concept of kin selection is used to explain the existence of sterile workers in social ants, bees, and wasps.
Ants, bees, and wasps have an odd genetic system such that females are diploid and males are haploid. This means that females of these insects (workers in social groups) share, on average, more genes with their sisters (3/4) than they would with daughters (1/2). It can thus be argued that workers in ant, bee, and wasp societies can pass more of their genes on to the next generation by foregoing their own reproduction, and instead staying in the colony to help their mother produce their sisters, some of whom will become future queens.