GENETICS REVIEW (KEY)
MONOHYBRID PROBLEMS
1.
If in pea plants, G=green pods and g = yellow pods, what would be the genotypic and phenotypic
results of this cross:
Gg X GG
offspring genotype probabilities: Gg 50% / GG 50%
offspring phenotype probabilities: Green 100%
2.
If in pea plants T=tall and t=short, what would be the genotypic and phenotypic results of this cross:
Tt X Tt
offspring genotype probabilities: TT 25% / Tt 50% / tt 25%
offspring phenotype probabilities: Tall 75% / Short 25%
3.
Cross a white seed plant with a heterozygous brown seed plant. (b = white, B = brown)
offspring genotype probabilities: Bb 50% / bb 50%
offspring phenotype probabilities: Brown 50% / White 50%
4.
In watermelons, green-skinned fruit is due to the dominant gene "G", while striped skin is due to its
recessive allele, "g". If you cross a homozygous green-skinned watermelon plant with a homozygous
striped one, what F1 results (genotype and phenotype) would you expect?
Genotype: Gg
Phenotype: Green
Crossing two F1 individuals would give the F2 generation. What is the F2 genotype results (genotype
and phenotype)?
Genotypes: GG / Gg / gg
Phenotype: Green / Striped
5.
In fruit flies, long wing is dominant over vestigial (short) wing. If two flies heterozygous for this trait are
crossed, what is the probability that their offspring will be heterozygous? 50%
6.
In squash, the allele for white fruits (W) is dominant over the allele (gene) for yellow (w). If a whitefruited plant is crossed with a yellow-fruited plant and all the offspring are white, what are the possible
genotypes of the parents and the offspring?
a.
parents genotype: WW x ww
b.
offspring genotype: Ww
7.
The genetic disease called cystic fibrosis is inherited through a recessive gene. If both parents are
heterozygous for this trait, what is the probability that they will have a child who suffers from this
disease? (C = normal, c = cystic fibrosis) 25%
8.
In cats, the gene for short hair is dominant over the gene for long hair (angora) (S = short hair, s = long
hair). A short-haired tom cat is mated with an angora female. She bears eight kittens, six are shorthaired and two are long-haired. How do these numbers compare with the expected ratio?
Ss x ss = 1:1(2:2) ratio of short to long hair. Does not match ACTUAL ratio of 3:1(6:2)
If you mated these cats four more times and obtained a total of forty offspring, would the results be a
closer approximation of the expected ratio? Explain.
Yes, the higher the number of the sample, the closer it will get to the predicted ratio.
Give the genotype of the tom cat, the female, and the kittens.
Tom Cat = Ss
Female Cat = ss
Kittens = Ss or ss
9.
Some dogs bark while they are trailing an animal. Others are silent. The barking trait is inherited from
a dominant gene. A barker, who had a silent mother is mated to a silent trailer. The female bears four
puppies. What are the chances that there will be silent puppies in this group? Explain and show the
cross? (B = barker, b = silent) Bb x bb = 50% bb (silent puppies)
10.
Brown hair color is dominant to blond hair color. If two brown-haired parents have one blond-haired
child, what is the probability that their second child will have brown hair? (B = brown, b = blonde)
Bb x Bb = 75% Bb or BB (brown hair)
INCOMPLETE OR CODOMINANT PROBLEMS
1.
In a certain type of flower, color is incompletely dominant. Cross a pure red flower with a pure white
flower. What will be the phenotype of the offspring? (R = red, W = white) Pink
2.
In flowers, color is an incomplete dominance trait. (see above problem) When the genotype is
heterozygous, the phenotype is pink. Cross a pink flower with a pink flower. What will be the genotype
and the phenotype of the offspring?
Genotype: RR / RW / WW
Phenotype: Red / Pink / White
3.
When a pure red cow is bred with a pure white bull, the F1 offspring is a roan (this means that it has
both red and white hairs). What will be the results of a cross between a red bull and a roan cow?
RR x RW = Genotype: RR 50% / RW 50%
Phenotype: Red 50% / Roan 50%
Could a farmer raise a herd of roan cattle that would only produce roan offspring? Explain. (R = red
hairs W = white hairs) No, will always produce 25% Red, 50% Roan, and 25% White
4. In Guppy vultures, pure long legs when crossed with pure short legs cause medium legs. Cross a long
Guppy vulture male with: 1. a medium hen and 2. a short hen and give the phenotype of the offspring.
(L = long legs, S = short legs)
1) LL x LS = Long Legs / Medium Legs 2) LL x SS = Medium Legs
SEX-LINKED PROBLEMS
1.
Show, using a Punnett Square, how the sex of a child is determined. Does the egg from the mother or
the sperm from the father determine the sex of the offspring? Dad
X
Y
X
XX
XY
X
XX
XY
2.
Color blindness is a sex-linked recessive trait. What is the probability that a color blind woman and a
color-blind man will have: a. a normal sighted son b. a color blind daughter
XcXc x XcY = a) 0% b) 100%
3.
What is the probability that two parents with normal color vision will have color blind sons or daughters
if the mother's father is color -blind? XCXc x XCY = 25% Colorblind Children
4.
Hemophilia is a sex-lined blood disorder. People with this disease can bleed to death from a small cut
because their blood does not clot. It is caused by a recessive allele. You are a normal (homozygous)
female who is about to marry a hemophiliac male. What are your chances of having a child with this
blood disorder? (XH= normal blood Xh= hemophilia) XHXH x XhY = 0% Hemophiliacs
5.
In Drosophila, the gene for red eye color, R, is dominant to the gene for white eye color, r. The trait is
sex-linked. A red-eyed male was bred to a heterozygous red-eyed female. Mark true/false.
XRXr x XRY
The genes for eye color are carried on the X chromosome. True
The male's genotype is XRYr. False
The female's genotype is XRXr. True
Half of the gametes produced by the female should contain Xr. True
All the gametes produced by the male should contain Yr. False
Of the offspring produced, all females are expected to have red eyes. True
Of the offspring produced, all males are expected to have white eyes. False
The offspring of a white-eyed male must have the genotype XrY. True
Female offspring produced from this cross could have the genotype XrXr. False
MULTIPLE ALLELE PROBLEMS
1.
If a man with blood type AB marries a woman heterozygous for type A, what is the probability that their
child will be type B? IAIB x IAi = 25% Type B
2.
A mother has type A blood and a father has type B blood. If their baby has type O blood, what is the
genotype of the parents? IAi x IBi
3.
Use a Punnett square to show the possible genotypes and phenotypes for blood type of the offspring of
two parents, one with blood type O and one with blood type AB.
IAIB x ii = Genotypes: IAi / IBi
Phenotypes: Type A / Type B
4.
Two women gave birth to girls in the same hospital at the same time. The nurses think they may have
accidentally switched the babies' name tags and given the babies to the wrong parents. One baby,
Jane, is type O. The other baby, Mary, is blood type A. The father in one set of parents, the Reds, is
blood type A, and the mother is type B. The father in the other set of parents, the Greens, is blood type
AB, and the mother is type O. Figure out which baby belongs to which parents. Show your work and
reasoning. Jane cannot be Greens baby b/c father is type AB. Jane is a Red. Mary is a Green.
PEDIGREE PROBLEMS
1.
Determine the genotypes of each of the following 12 individuals (color blindness is sex-linked)?
B
A or B
2.
B
C
C
D
D
B
C
B
C
E
A = XCXC
B = XCXc
C = XCY
D = Xc Y
E = XcXc
The following is a pedigree of myopia (near-sightedness). This condition is caused by a recessive
gene, but is NOT sex linked. Determine whether the 8 individuals are A. Heterozygous B.
Homozygous C. Not enough sufficient data to determine genotype.
A
A
C
A
B
A
B
A
3.
Huntington’s Disease is caused by a dominant gene. (not sex linked) Based on the laws of
probability, what are the likely genotypes of the numbered individuals?
H_
Hh
hh
4.
hh
Hh
A = HH
B = Hh
C = hh
hh
This pedigree below shows the blood types of some individuals. List all the possible genotypes of each
numbered individual.
IAi
IBi
IAIB
IBi
IAi
IBi
CHALLENGE PROBLEMS
1.
What kind of gametes (sperm) could a man who was heterozygous for long eye lashes, free earlobes,
and brown eyes produce? LEB, LeB, LEb, Leb, lEB, leB, lEb, leb
If he were to marry a woman of exactly the same genotype for these 3 traits, what size Punnett square
would be needed? DO NOT ACTUALLY MAKE THE CROSS!!!!!! 8 x 8
2. In cocker spaniels, white spotting is recessive to solid color. You want to know if your red solid-colored
cocker is homozygous or heterozygous for spotting. How could you find out?
You need to do a test cross with a homozygous recessive (spotted) dog.
If yours is homozygous, what results would you expect? 100% Red
If yours is heterozygous, what results would you expect from the cross? 50% Red / 50% Spotted
3. In poultry, feathered legs (F) are dominant over clean legs (f) and pea comb (P) are dominant over
single comb (p). Two cocks, A and B, are bred to two hens, C and D. All four birds are feather legged
and pea combed. Cock A with both hens produced offspring that are feathered and pea combed. Cock
B with hen C produced both feathered and clean, but all pea combed, but with hen D he produced all
feathered, but part pea combed and single. What are the genotypes of all four birds?
Cock A = FFPP, Cock B = FfPp , Hen C = FfPP, Hen D = FFPp