Honors Biology
Genetics Homework
Answer the following questions (in complete sentences). Some questions may require outside research.
Mendelian Genetics
1. What is the difference between an allele and a gene?
2. What is the difference between genotype and phenotype?
3. Why was the pea plant an excellent subject for Mendel’s experiments?
4. Describe Mendel’s Law of Segregation. [N.B.- This is one of two very important ideas in this chapter, so
make sure you do this well!]
5. What is a test cross?
6. You have two true-breeding lines of plants. One produces red fruit, the other yellow fruit. Describe
how you would test to see whether yellow or red fruit is dominant.
7. In pea plants, purple flowers are dominant to white flowers. You mate two pea plants with purple
flowers together and get plants with white flowers and plants with purple flowers. What percentage of
the offspring would be white?
8. When a dog with a yellow coat mates with a dog with a brown coat, all the puppies have brown coats.
Tell me everything you can about the genotypes of the parents and puppies.
9. Describe Mendel’s Law of Independent Assortment. [N.B.- This is the other very important idea, so make
sure you do this well!]
10. You mate a tall pea plant with purple flowers (TtPP) with a short pea plant with purple flowers (ttPp).
Use a Punnet square to calculate all possible offspring. Tell me the phenotype of all the offspring, and
the probability that they would appear.
11. In flies, a mutation causes the wings to curl up and become useless. You mate a normal male fly with a
mutant female fly. All the offspring flies (the F1) are normal. You then sib-cross two F1 flies together,
and find 73 normal flies and 28 curly-winged flies.
What is dominant?
What are the genotypes of the parental flies?
What are the genotypes of the F1 flies?
Draw the Punnet square for the F2 cross.
12. You mate an organism with the genotype AaBb with another AaBb. If they have 48 offspring, how many
of them would you expect to have the genotype aabb?
13. Guinea pigs can have two different types of coats: a soft, smooth coat and a spiky, rough coat. You mate
a rough coated female with a smooth coated male. 50% of the offspring have rough coats, and 50%
have smooth coats. Tell me everything you can about the genetics of these guinea pigs.
14. Geneticists must sometimes calculate out the possible offspring of crosses involving many more than
two genes. These Punnet squares can be huge! Calculate out all the possible gametes (egg or sperm
combinations) that are possible from an organism with the genotype AaBbCc.
Those using a textbook will find relevant material in Chapter 12, sections 1-2.
Nonmendelian genetics
As you study the different types of non-Mendelian inheritance, note the major differences between them. You must be
able to identify the correct inheritance pattern when presented with a problem on the test.
I do not expect you to memorize all the human genetic disorders. I expect you to be able to define the disease and the
genetics for hemophilia (sex linked), sickle-cell anemia (codominance—though in more advanced courses you will discover
that it is not really codominance), and color blindness (sex linked). I also want you to understand the human ABO blood
typing system, which we have talked about already.
15. Far more males develop baldness than females. What does this imply about the location of the gene (or
genes) that affect baldness?
16. You cross a plant with a yellow flower and a plant with a white flower. All of the offspring have light
yellow flowers. What type of inheritance is this? What offspring would you expect, and how many, if
you were to cross two light yellow siblings?
17. You are studying a small species of mice. You notice that some of the mice have darker coats than
others. You perform a cross between a normal female and a dark male, and find that every one of the
baby mice are normally colored. When you cross the siblings from the F1, you find that one quarter of
the mice are dark. But you notice something odd—only males have the dark coloring.
Explain the inheritance pattern.
Calculate out the genotypes of the original parents and the genotypes of the F1 mice.
18. In the old days (before DNA sequencing) blood tests were often used to identify the father in paternity
suits. Assume you have a woman with type A blood who has a baby with type O blood. There are two
possible fathers: one with type B blood and the other with type AB blood. Can you determine who the
father must be?
19. You are studying a small lizard that lives in the rain forest. It has a brown skin color to better hide in the
jungle. You set out to do a genetic analysis of the skin tone—how it is inherited. You collect 100 lizards
from the jungle, but when you try to sort them you realize that they only have slightly different
colorings. Analysis is pretty much impossible at this time. Offer a possible genetic source of this wide
range of color variations.
20. Some disorders are not caused by mutant genes, but by having too many chromosomes (e.g., trisomy X
and trisomy 21). Although the chromosomes are perfectly fine, the individual is not. Since the
chromosomes do not encode faulty genes, think of another reason why people with these conditions
may be ill.
Trisomy 21 and Trisomy X occur in humans, but differences in numbers of the other 21 chromosome
pairs in humans are very rarely seen. (For example you do not find Trisomy 1). Offer a reason why. [I
can think of two].
What causes these errors in chromosome number?
21. You are studying a type of pine tree in California. You notice these trees can produce either brown or
green cones. They also can have either three or five bundles of needles on each branch. As you study
the pine trees, you notice that you tend to only see trees that have green cones and three bundles, OR
trees with brown cones and five bundles. What does this tell you about the inheritance of these genes?
You find a few trees that have recombined the traits (i.e. have brown and three, or green and five) but
these are very rare. What process led to this rare shuffling of genes?
Those using a textbook will find relevant material in sections 12.6-12.9.