Download Genetics Problem Set #1

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Genetics Problem Set #1
1. How many genes does each body cell have for each trait? ____________
2. How many genes does each gamete have for each trait?_____________
3. What process separates the homologous chromosomes and therefore the
two genes (alleles) in a gene pair during gamete formation?_____________
4. What is an allele?
5. Define dominant allele and give an example of a specific dominant allele:
6. Define recessive allele and give an example of a specific recessive allele:
7. Using a Punnett square, figure out the expected offspring of mating a
pure (homozygous) black guinea pig with a heterozygous (hybrid) one, who is
also black in color. Use the key B-black, b-white. Indicate the phenotype
(appearance) in words next to the genotype in the Punnett square.
8. In chickens, white is dominant and red is recessive. W-White and w-red.
Cross two hybrids (individuals which are heterozygous for the trait; that is,
they carry two different genes for the trait).
Their genotype would be Ww. You are making an F1 cross of monohybrids.
Their offspring can be considered F2 or second generation.
9. In some cases, diabetes is an inherited disease. Diagram a cross between
a man heterozygous for this gene and a diabetic woman. (N=normal;
n=diabetic. Note: diabetes is recessive). What is the probability that their
first child will be diabetic?
10. In humans, the allele for brown eyes is dominant to the allele for blue
eyes. A woman with blue eyes marries a man with brown eyes and they have a
blue-eyed child. What is the genotype of the mother? What is the
genotype of the father? What is the probability that their next child will
have blue eyes?
11. Use B-Brown eyes and b-blue eyes. Nancy has blue eyes. Two of her
sisters and three of her brothers have brown eyes. Nancy’s father has blue
eyes.
What is the mother’s genotype? _________________
What is her eye color? ________________________
How did you figure this out?
Can two blue-eyed parents have a brown-eyed child? Explain.
12. Diagram a cross between two parents who are heterozygous for curly
hair. (H=curly; h=straight). What is the probability that the couple’s second
child will have straight hair?
13. If in sheep, white coat color is dominant, and black is recessive, let
W=white and w=black. I mate a white sheep with a black sheep and the
offspring are one white and one black.
What is the genotype of the white parent? _____________________
How did you determine this? Explain fully.
If two black offspring are born, what is the genotype of the white
parent? _________________
If two white offspring are born, what can I say about the genotype
of the white parent? _________________________________________
14. Thalassemia is a type of human blood disease common in Mediterranean
populations. The disease occurs in two forms –minor and major (severe).
Severely affected persons are homozygous for a recessive allele; mildly
affected persons are heterozygous; persons free of the disease are
homozygous for the normal, dominant allele.
A. A man with Thalassemia minor marries a normal woman. What types of
children and in what proportions might they expect?
B. A child has Thalassemia major. What possible genotypes might its
parents be?
C. If both parents have Thalassemia minor, what is the chance that their
baby will be severely affected? Mildy affected? Normal?
15. A red-haired man (Harry), both of whose parents (Laura and William)
have brown hair, marries a brown-haired woman (June) whose father (Frank)
has brown hair and whose mother (Cindy) has red hair. Harry and June have
one child (Peggy) who is red-haired. Assuming that brown hair is dominant
over red hair, give the genotype of as many of the seven people of this
family as you can.
16. In guinea pigs, black coat color is dominant. Use the key B=black,
b=white. I have a black male guinea pig and I am not sure of its genotype.
What are the two possibilities for its genotype? ____________ and
___________.
Exactly how can I determine its genotype? _____________________
Show which mating must be made and indicate how the offspring can be used
to determine the father’s genotype.
17. Problem: You have a pure white rat – a rat whose ancestors for many
generations back have been white. You can also have a pure black rat (with
all black ancestors). How can you find out which color is dominant in coat
color in rats. Explain exactly what to do and what the results would tell you.
Once you determine which coat color, black or white, is dominant in rats, can
you now also conclude that this same thing would be true for coat color in
dogs, for example?
18. In some species of plants, if an individual with red flowers (RR) is
crossed with an individual that has white flowers (rr). All the offspring have
pink flowers (Rr). There is no dominance between red and white alleles.
What will be the results of the following crosses?
A. red x red ____________________________
B. red x pink ___________________________
C. pink x pink ___________________________
19. What is meant by the term Incomplete Dominance? What is meant by
Co-Dominance? Distinguish between them and give an example of each:
20. In radishes, there is no dominance. The genes are R-red and W-white.
Use a punnett square to show the offspring of the following parents:
RR
X
RW (Note: RW appears purple)
21. If I want to obtain 100% purple radishes, show the genotype of the
parents that I must cross to obtain seeds that will grow into all purple
radishes.
22. In the flowering plant, Four O’clocks, there is no dominance shown
between the red gene for petal color and the white gene. A genotype of RW
gives pink flowers. I buy some seeds that are guaranteed to give all pink
flowers. I plant them and all my plants bear pink flowers. The plants selfpollinate and I collect the seeds. I plant these seeds (a great number of
them) the next year. What color(s) can I expect and what % of each? Use a
Punnett square.
23. We are now ready to follow two traits at the same time. These two
traits are on two different chromosomes. They will assort independently (go
their own way) during meiosis.
Starting with a pure (homozygous) Black (B), Rough-haired (R) guinea
pig, and mate it with a pure white (b) smooth (r) one. The genotypes of these
P ‘s would be BBRR x bbrr. The gametes of these P ‘s would have one gene
for each trait. All eggs are BR, all sperm are br. All F1 offspring are BbRr
(Black and Rough). Dihybrid or heterozygous for 2 traits.
Now mate two these F1 s. Use a large (16 box) Punnett square.
Genes in egg

BR
Br
bR
br
Genes in
sperm
(below)
BR
Br
bR
br
Fill in the chart with these F2 s. Keep genes for coat color first. List all
phenotypes and give their ratios below: