Download GENETICS PROBLEMS sheet 1

GENETICS PROBLEMS sheet 1
SOLVE THE FOLLOWING PROBLEMS AS ASSIGNED ON
THE CALENDAR AND BOARD: SHOW ALL WORK FOR
FULL CREDIT.
1.In squash, an allele for fruit with white color (W) is dominant over the allele for
yellow color (w). Use a punnett square to show a cross between a
homozygous white-fruited plant and a heterozygous plant. What is the ratio
of genotypes among the offspring? What is the ratio of phenotypes?
2. A gardener has a white-fruited squash plant he wants to breed to obtain only
pure, white-fruited offspring. He doesn’t know, however, if the plant he has is
homozygous or heterozygous. Show how he could use a test cross to find
out.
3.In human beings, brown eyes (B) are dominant over blue eyes (b). Suppose
a blue eyed man marries a brown eyed woman whose father was blue eyed.
What ratio of blue to brown eyed children would be predicted for the couple?
If they have brown eyed children, would they be homozygous or
heterozygous?
4. What would be the expected ratios of genotypes and of phenotypes among
the children if two heterozygous brown eyed people were to marry?
5. In peas, an allele for tall plants (T) is dominant over the allele for short (t) and
the allele for smooth peas (S) is dominant over the allele for wrinkled peas
(s). Show a Punnett Square for each of the following crosses, and give the
ratios of genotypes and of phenotypes among the expected offspring.
a.
TT X tt
b.
Tt X Tt
SS
ss
SS
ss
c.
TT X tt
ss
SS
d.
Tt X Tt
Ss
Ss
6. In fruit flies, normal wings (N) are dominant over vestigial wings (n) and
hairless body (H) is dominant over hairy (h). Suppose a vestigial-winged,
hairy male is crossed with a female homozygous dominant in both traits.
What would be the nature of the F1 generation in phenotype and genotype?
What would be the genotype and phenotype ratios of the F2 generation?
7. Use probabilities, NOT Punnett squares, to find the following:
a. the probability of a gamete with the genes aBC from an individual with the
genotype AaBBCc.
b. from the cross AaBbCC X aaBbcc, what are the probabilities of the
following offspring: AABBCC ?
aabbCc ?
AaBbCc?
8. Two fruit flies are mated, and among the offspring there are 145 hairy flies and
372 hairless. What are the most likely genotypes of the parents in this cross?
2
There are two possibilities. Show a Chi test of each and choose the best one
based on the results of the test. (see probability table, next page.)
9. The litter resulting from the mating of two short-tailed cats contains three kittens
without tails, two with long tails, and six with short tails. What would be the
simplest way of explaining the inheritance of tail length in cats? Show the above
cross on a Punnett square.
10. In shorthorn cattle, there are three coat colors: red, white, and roan (a mixture
of red and white hairs). Show the mating of a roan bull and a white cow. What
is the probability of a red calf? A white calf? A roan calf?
11. Suppose the mating in the previous question produced twins (non-identical).
What would be the probability of each of the following combinations of colors for
the twins? red & red?
roan & roan?
e & white?
roan & white?
12. If a man with blood type B, one of whose parents had blood type O, marries a
woman with blood type AB, what will be the predicted percentage of their
children with blood type B?
13. Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital.
Mrs. Smith took home a baby girl, whom she named Shirley. Mrs. Jones took
home a baby girl, whom she named Jane. Mrs. Jones began to suspect,
however, that her child had been accidentally switched with the Smith baby in the
nursery. Blood tests were made:
Mr. Smith: A
Mrs. Smith: B
Shirley: O
Mr. Jones: A
Mrs. Jones: A
Jane: B
Had a mixup occurred? What are the genotypes for everyone?
14. In fruit flies, there is a dominant allele for gray body and a dominant allele of
another gene for normal wings. The recessive alleles of these two genes result
in black body color and vestigial wings, respectively. Flies that are homozygous
for gray body and normal wings were crossed with flies that had black bodies and
vestigial wings. The F1 offspring were then test crossed (review the meaning of
this term) with the following results among the offspring:
Gray body, normal wings: 236
Gray body, vestigial wings: 50
black body, normal wings: 61
black body, vestigial wings: 253
Are the genes for body color and wing shape linked? If so, how many map units
apart are they on the chromosome?
15. In rabbits, the dominant allele of a gene produces spotted body color, and
the recessive allele produces solid body color. The dominant allele of another
gene produces short hair, and the recessive allele produces long hair.
Rabbits heterozygous for both characteristics were mated with homozygous
recessive rabbits with the following offspring:
spotted, short hair
96
solid, long hair
80
solid, short hair
14
spotted, long hair
10
What evidence for linkage is shown in this cross? Give the percentage of
recombination and the map distance between the genes.
16. In fruit flies, the genes for bristle shape and for eye color are known to be
about 20 map units apart on the same chromosome. Individuals homozygous
dominant for these genes were mated with homozygous recessive individuals.
The F1 progeny were then test crossed. If there were 1000 offspring from the
test cross, how many of the offspring would you predict would show the
crossover (recombinant) phenotype combination?
17. The recombination frequency between linked genes A and B is 40 percent;
between B and C, 20 percent; between C and D, 10 percent; between C and
A, 20 percent; between D and B, 10 percent. What is the order of the genes
on the chromosome?
18. Red/green color blindness is a sex linked recessive. If a colorblind woman
marries a man who has normal vision, what would be the expected
phenotypes of their children, for boys and for girls?
19. Suppose that an allele, b, of a sex linked gene is recessive and lethal. A
man marries a woman who is heterozygous for this gene. If this couple had
many normal children, what would be the predicted sex ratio of the children?
20. A man and his wife both have normal color vision, but a daughter has
red/green color blindness. The man sues his wife for divorce on grounds of
infidelity. Can genetics provide evidence supporting his case?
21. In cats, short hair is dominant over long hair. The gene involved is
autosomal. An allele, B1, of another gene, which is sex-linked, produces
yellow coat color. The allele B2 produces black coat color. The heterozygous
combination B1B2 produces tortoiseshell (calico). If a longhaired black male is
mated with a calico female homozygous for short hair, what kind of kittens will
be produced in the F1?
A challenge: If the F1 cats are allowed to interbreed freely, what are the
chances of obtaining a longhaired yellow male? (This one has reduced grown
biologists to tears! A hint: use probabilities, not a Punnett square.)
22. It is extremely difficult to tell the sex of very young chickens, but it is easy to tell,
by observation, if they are barred. Barring is a feather pattern that is inherited as
a sex-linked dominant trait. Set up a cross that would always allow the sex of
chicks to be determined at hatching because barred chicks would always be one
sex and nonbarred chicks the other. (Remember, chickens are birds!)
23.
The pedigree shows three generations of the pedigree of deafness in a family.
Shading indicates deafness. How is the condition inherited? Defend your
selection. a. dominant autosomal b. recessive autosomal c. X-linked
recessive d. X-linked dominant
e. Y-linked
Hardy-Weinberg problems for “Genetics of Evolution” unit
24. The frequency of two alleles in a gene pool is 0.1A (=p) and 0.9a (=q). What is
the percentage in the population of heterozygous individuals, Aa (2pq)? Of
2
homozygous recessives, aa (q )? Of homozygous dominant, AA (p2)? Assume
the population is in Hardy-Weinberg equilibrium.
25. In a population that is in genetic equilibrium, 36 percent of the individuals are
recessive homozygotes for a certain trait. For the same trait, what is the
percentage in this population of homozygous dominant individuals? Of
heterozygous individuals?
26. Allele T, for the ability to taste a particular chemical, is dominant over allele t,
for the inability to taste it. At Cornell University, out of 400 surveyed students, 64
were found to be nontasters. What is the percentage of heterozygous students?
Assume the population is in equilibrium.
27. In humans, Rh-positive individuals have the Rh antigen on their red blood cells,
while Rh negative people do not. Assume that the Rh positive phenotype is
produced by a dominant gene R, and the negative phenotype is produced by r.
If 84 percent of the people in a population are positive, what are the frequencies
of each of these genes?
28. A rare disease due to a recessive allele which is lethal when homozygous
occurs with a frequency of one in a million. How many individuals in a town of
14,000 can be expected to carry this allele (to be heterozygous)?
29. In a population of rabbits, 13% have brown coats. Brown coat is dominant
over black. What percentage of the population is homozygous for brown coat?
30. Suppose that another population includes 147 rabbits. Among these rabbits,
there are 92 with black coats. How many rabbits in this population are
heterozygous?
31. Among unicorns, purple coat is dominant over pink. A certain population
contains 1232 purple unicorns and 963 pink. What is the frequency of the allele
for purple coat in this population?
32. In the population of unicorns above, how many unicorns are heterozygous?
33. In a population of toads, a yellow marking on the nose is a recessive trait. The
dominant allele, (B) gives a brown marking. The frequency of the yellow allele
is 0.36. Out of a population of 5236, how many toads will have the brown
marking?
34. Among horses, the trotting gait (T) is dominant over the pacing gait (t). In a
wild population of 678 horses, there are 53 pacers. How many of the trotters
are heterozygous?
35. What is the frequency of pacers in this population?
36. If another population has 1590 trotters and 537 pacers, what is the frequency
of the allele for trotting in this population?
37. How many homozygous trotters are in this second population?
38. In a wild population of Japanese 4 o’clocks, there are 986 plants with red
flowers out of the total population of 2791. How many plants with pink flowers
are there? How many with white flowers?
39. In a population of bats, 145 show the recessive allele for light brown coat, and
the remaining 298 have black coats. How many bats are homozygous for black
coat color?
40.A recessive allele for hitch-hikers thumb exists in a population of 3467 with a
frequency of .26. How many people in the population have straight thumbs?
41. How many people in the above population are heterozygous?
42. In a field of pea plants, 68% of the plants are short. What percent are
heterozygous tall?