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Heredity (Chapter 5) Study Guide
Part I: Vocabulary. Using the word bank below, match each word to its correct definition.
alleles
dominant
genetic engineering
recombinant DNA
genetics
genotype
heredity
heterozygous
homozygous
incomplete dominance
phenotype
polygenic inheritance
Punnett square
recessive
sex-linked gene
Gregor Mendel
1. The allele for hemophilia is on the X chromosome and is considered a sex-linked gene.
2. Heredity is the passing of traits from one generation to another.
3. The different forms a gene may have for a trait are called alleles
4. In incomplete dominance both alleles are expressed in offspring.
5. Gregor Mendel is known as “The Father of Genetics”.
6. A dominant trait covers up other traits.
7. In a Punnett square, a small letter (t) stands for a recessive allele.
8. A tool used to predict the possible offspring of a mating is called a Punnett Square
9. The genetic makeup of an organism is called its genotype
10. Phenotype is the way an organism looks and behaves a result of its genotype.
11. The study of how traits are inherited through the interactions of alleles is genetics
12. Through genetic engineering scientists are experimenting to change the arrangement of DNA in a gene.
13. An organism with two alleles that are exactly the same is homozygous
14. Polygenic inheritance occurs when a group of gene pairs acts together to produce a single trait (Examples
include height and skin color).
15. An organism that has two different alleles for a trait is heterozygous
16. A type of genetic engineering where a useful gene is inserted into a bacterium is known as
Recombinant DNA
Part II: Punnett Square Practice Problems. For each problem below you must write down your “cross” and a
punnett square. Box or circle the final answer.
17. In silkworms, the dominant allele for cocoon color is yellow (Y), and the recessive allele is white cocoon (y).
If white cocoon silk worm is crossed with a homozygous dominant yellow cocoon silk worm, what will be all
the possible genotypes and phenotypes of the offspring?
Yy x YY gives a punnett square with all Yy offspring.
Genotypes: Yy
Phenotypes: All yellow
18. In mice, the dominant allele for eye color is black (B), and the recessive allele is red eyes (b). If two
heterozygous parents are crossed, what will be the probability of the offspring having red eyes?
Bb x Bb gives a punnett square with offspring: BB, Bb, Bb, and bb
bb is red eyes, ¼ have red eyes or 25%
19. A widow’s peak (W) hairline is dominant to straight hairline (w). A straight hairline person is crossed with
another person who is heterozygous for the trait. What is the probability of the offspring having a widow’s
peak?
ww x Ww gives a punnett square with offspring: Ww, Ww, ww, ww
Ww is a widows peak, 2/4 have widow’s peak or 50%
20. Sex-Linked Punnett Square. Colorblindness is inherited as a sex-linked recessive disease. An affected male
marries a heterozygous female. Use b for color blindness, and use B for normal.
What is the genotype of the male (remember you put the genes on top of the X chromosome): XbY
What is the genotype of the female: XBXb
Draw and complete the punnett square below:
Set up just like a regular punnett square, except keep the X’s and Y’s. See warm up about sex-linked punnett
squares for an example.
What is the probability that the daughters will be color blind? ½ or 50%
What is the probability that the sons will be color blind? ½ or 50%
Part III: Short Answer. Respond to each question/prompt completely in the space provided.
21. The pedigree below shows how color-blindness (a sex-linked disorder) is spread through this family. Use
this pedigree to answer the questions.
a. How many individuals in the pedigree are affected with color blindness? 2
b. How many individuals in the pedigree are male? 7
c. How many individuals in the pedigree are female? 6
d. How many females are affected with color blindness 0
e. All of the carriers are which sex? Why is that the case?
Female. Only females can be carriers of sex-linked traits because they have 2 X chromosomes. They must
carry both the dominant and recessive allele to be a carrier. Since males only have 1 X chromosome, they
cannot carry both alleles.
22. How is incomplete dominance different from the patterns observed by Mendel?
In incomplete dominance, alleles are not dominant or recessive, they blend together. Mendel observed that
some traits were dominant and masked other traits (recessive) when they were inherited together.
23. Genetic counselors help individuals determine the risk of passing a disease on to their offspring. What
would a pedigree be a useful tool for a genetic counselor?
It can show them how a trait is passed through an entire family through the generations.
24. Do you agree with genetic testing for diseases? Use specific evidence from class discussions, the video, or
class readings to support your answer.
Answers may vary, opinion based on observations from class. Some pros include being able to plan ahead
and possibly find a treatment. Cons include getting excluded and stereotyped because of what is in your
genes.