AP Biology
Basic Genetics Problems
Read Chapter 8 in Principles of Life.
You should be able to do these as a starting point for this unit. If these are difficult try this
website for a review: http://biology.clc.uc.edu/courses/bio105/geneprob.htm. The link to this
site is “Basic Genetics Review” on my webpage.
Complete the questions on a separate piece of paper. ALL work or an explanation should be shown.
Credit will no be given for answers only.
1) A) A homozygous tomato plant that had spherical fruits (SS) was crossed with one that had pearshaped fruits (ss). All the F1 plants had spherical fruits. What was the genotype of these F1 plants?
B) If two of these F1 plants were crossed, about what proportion of the resulting plants would have
spherical fruits?
C) A tomato plant of unknown genotype, but bearing spherical fruits, was crossed with one that had pearshaped fruits. This cross resulted in 131 plants with spherical fruits and 134 plants with pear-shaped
fruits. What were the genotypes of the parents?
D) A tomato plant that had spherical fruits was crossed with another that also has spherical fruits. The F1
generation resulting from this cross consisted of 127 plants with spherical fruits and 41 plants with pearshaped fruits. What were the genotypes of the parents?
2)In humans, the allele for short fingers is dominant over that for long fingers. If a person with short
fingers who had one parent with long fingers marries a person with long fingers, what are the chances of
their children having short fingers?
3) Two black female mice were bred with the same brown male. In three litters, female A produced 9
black mice and 7 brown ones while female B produced 19 black mice. What conclusions can you draw
about the genotypes of the parents? Assume that black is dominant over brown.
4) In summer squash, white fruit (W) is dominant over yellow fruit (w), and disc fruit shape (D) is
dominant over sphere fruit shape (d).
A) Crossing a homozygous white-fruited plant with a yellow-fruited plant will give?
B) Crossing two heterozygous disc-fruited plants will give?
C) Crossing a heterozygous disc-fruited plant to a sphere-fruited plant will give?
D) Crossing two yellow-fruited plants give?
E) The genotype of a white, sphere-fruited plant could be?
F) Crossing a heterozygous white and heterozygous disc-fruited plant with a yellow,
sphere-fruited plant will give?
1
5) In Jimson weed, the gene that bears the potential for violet petals (V) is dominant over that for white
petals (v), and the gene that bears the potentiality for prickly capsules (S) is dominant over that for
smooth capsules (s). A plant with white petals and prickly capsules was crossed with one that had violet
petals and smooth capsules. The F1 generation was composed of 47 plants with white petals and prickly
capsules, 45 plants with white petal, and smooth capsules, 50 plants with violet petals and prickly
capsules, and 46 plants with violet petals and smooth capsules. What were the genotypes of the parents?
6) How many different kinds of gametes can an organism of genotype RrSS produce? BBgg produce? PpSs
produce? AaBBCcddEeFfGg? (try probability please)
7) In guinea pigs rough coat (R) is dominant over smooth coat (r), and black coat (B) is dominant over
white (b). A rough, black guinea pig bred to a smooth, white one gave 28 rough, black; 31 rough, white; 31
smooth black; 29 smooth, white. What were the genotypes of the parents?
8) In four o'clocks, red flower color (R) is only partially dominant over white (R'), the heterozygotes
being pink. What would be the genotypic and phenotypic ratio of the offspring from two pink parents?
9) Suppose you learn that radish plants produce long, oval, or round radishes and that from crossing
radish plants you get the following results:
long X oval gives 52 long and 48 oval
long x round gives 99 oval
oval X round gives 51 oval and 50 round
oval x oval gives 24 long, 53 oval, and 22 round
What inheritance pattern explains these results?
10) Suppose a man with blood type A marries a woman who has type O blood. What are the possibilities
of blood types for their offspring?
11) If two newborn babies were accidentally mixed in the hospital, and in an effort to determine to which
parents each baby belonged, the blood types of the babies and the parents were determined. From the
information listed below, determine which baby belongs to which parents, and show the genotypes of all
individuals when solving the problem.
Baby #1 ............................................. Type O
Baby #2 ............................................. Type A
Mrs. Brown...................................... Type B
Mr. Brown ....................................... Type AB
Mrs. Smith....................................... Type B
Mr. Smith......................................... Type B
12) A man of blood group A marries a woman of blood group B, and they have a child of blood group O.
What are the genotypes of these three people? What other genotypes, and in what frequencies, would you
expect among the children of such a marriage?
13) Human color-blindness is a sex-linked, recessive trait. (a) What is the probability that a woman with
normal vision whose father was color-blind but whose husband has normal vision will have a color-blind
son? (b) A color-blind daughter?
14) The gene for white eye color in fruit flies is sex-linked and recessive to normal red eye color. Give the
results of the following mating:
A) a heterozygous red-eyed female with a red-eyed male
B) a white-eyed female with a red-eyed male
C) a heterozygous red-eyed female with a white-eyed male
15) In humans, color blindness is a sex-linked recessive trait, and widow's peak tan autosomal trait) is
dominant over continuous hairline. A man with normal vision and a widow's peak married a woman who
is color blind and has a continuous hairline. The woman has a girl who has a widow's peak and is color
blind. What are the possible genotypes of all persons involved. Is the husband the girl's father? How do
you know?
16) For each of the following genotypes, give all genetically different gametes, noting the proportion of
each for the individual. WW, Ww, Tt, TT
17) For each of the following, state whether a genotype or a gamete is represented. TT; D; GG; P.
18) In rabbits, if B = dominant black allele and b = recessive allele, which of these genotypes could a white
rabbit have? Bb, BB, bb.
19) In horses, trotter (T) is dominant over pacer (t). A trotter is mated to a pacer, and the offspring is a
pacer. Give the genotypes of all horses.
20) In humans, freckles is dominant over no freckles. A man with freckles reproduces with a woman with
freckles, but the children have no freckles. What chance did each child have for freckles?
21) In pea plants, yellow seed color is dominant over green seed color. Give the genotype of all plants that
could possibly produce green peas when crossed with a heterozygote (Y = yellow, y = green).
22) Match the offspring phenotypic ratio with the cross that would produce it:
a. 3:1
b. 9:3:3:1
c. 1:1
d. 1:1:1:1
1. TtYy X TtYy
2. TtXTt
3. Tt X tt
4. TtYy X ttyy
23) Which of these could be a gamete? GgLl, GLl, Gl, ggll
24) Which of these properly describes a cross between an individual who is homozygous dominant for
hairline but heterozygous for finger length and an individual who is recessive for hairline and fingers?
(Note: W = widow’s peak, w = continuous hairline, S = short fingers, s = long fingers)
a. WwSs X WwSs
b. WWSs X wwSs
c. Ws X ws
d. WWSs X wwss
25) In peas, yellow seeds (Y) is dominant over green seeds (y). In the F2 generation of a monohybrid
cross in which a dominant homozygote is crossed with a recessive homozygote, you would expect:
A) plants that produce 3 yellow seeds to every green seed.
B) plants with one yellow seed every green seed.
C) only plants with the either the genotype YY or yy.
D) Both a and c.
26) In humans, pointed eyebrows are dominant over smooth eyebrows. Mary’s father has pointed
eyebrows, but she and her mother have smooth. What is the genotype of the father?
a) Bb
b) BB
c) bb
d) Any of these.
27) In horses, B=black coat, b=brown coat, and T=trotter, t=pacer. A black trotter that has a brown pacer
offspring is:
a) BT
b) BbTt
c) bbtt
d) BBtt
28) In tomatoes, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over
shortness (t). A plant that is RrTT is crossed with a plant that is rrTt. What are the chances of an offspring
being heterozygous for both traits?
a) none
b) ½
c) 1/4
d) 9/16
29) If a plant with an RrTt genotype is crossed with a plant that is rrtt:
a) All the offspring will be tall with red fruit.
b) 75% will be tall with red fruit.
c) 50% will be tall with red fruit.
d) 25% will be tall with red fruit.
On my web page for Genetics, click on the link for “U of Arizona Genetics – problem sets”
complete the problems for the following sections and record your answers in the space provided.
Be sure to read the tutorials if you get the wrong answer.
I.
Monohybrid Cross
1.
10.
2.
11.
3.
12.
6.
10.
II.
Dihybrid Cross
1.
6.
2.
10.
3.
12.
5.
13.
Name __________________________________
III.
Sex-linked Inheritance I
1.
7.
4.
10.
6.
IV.
IV. Sex-linked Inheritance II
3.
4.
Next activity: Virtual Fly Lab
- go back to our resources and click on the Virtual Fly lab link
1. Begin by completing the following chart with the common Fly traits and their genetic
information
Trait
Inheritance
pattern
Variations
(Alleles)
MT or WT
Phenotypes
Wing
shape
Body
Color
Eye
Color
2. Compare the female and Male Flies. How do we determine the sex of a fly by examining
its phenotypes?
Name __________________________________
3. Now try out two of the crosses. The website can be a little glitchy, but fiddle around with
it and you can get it to work. Write your cross, the P1 genotypes, the F1
phenotypic/genotypic ratios and the F2 phenotypic/genotypic ratios below. Draw a
punnet square for each generation’s cross.
Cross 1(monohybrid): ____________________________
Cross 2: (MUST BE vestigial wing x ebony body dihybrid) ____________________________