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ANSWER KEY
Review Questions for 8th Grade Science Midyear Exam, Part I
(Due Tuesday, January 31, 2017) COMPLETION OF THIS ENTIRE PACKET IS WORTH A 20-POINT QUIZ!
NO LATE OR PARTIAL CREDIT WILL BE GIVEN!
Write your answers in the spaces provided. As answer keys will be provided on Tuesday, January 31, and answers will be
discussed in class, NO LATE CREDIT WILL BE GIVEN. Be prepared to ask questions!
Use your classwork, notes, homework, Discovery Education Techbook, the Internet, etc. to answer the questions.
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Question
Answer
Use the Punnett square:
It is controlled by a dominant allele, which means that if a seed has even
one copy of the allele for yellow seed color, then its seeds will be yellow.
1
Is yellow seed color controlled by a dominant
allele or a recessive allele?
2
3
4
Black fur is dominant in rabbits. What
combination of alleles must a white rabbit have?
The dominant allele for squash color is yellow (Y).
What is the genotype of a yellow squash plant
that is heterozygous?
Tall stem is dominant in pea plants. What are the
possible genotypes of a tall pea plant?
5
Black fur is dominant in guinea pigs. A homozygous
black guinea pig and a white guinea pig have offspring;
list the possible genotype(s) of their offspring.
6
For the offspring in #5, list the possible
phenotype(s).
7
Grasshoppers have 24 chromosomes in each of
their body cells. How many chromosomes are in
each grasshopper sex cell?
If black fur is dominant, then the white rabbit has to have two copies of the
recessive allele for white fur. Its genotype would have to be bb. BB or Bb would
be black.
Yy: A heterozygous genotype means that it has two different alleles for skin
color. The allele for green skin color (y) doesn’t show up in the phenotype because
it is recessive.
TT and Tt both result in a tall offspring. Tall is the dominant form of the height
gene, so having even one copy of the allele for tall results in a tall phenotype.
There is a 0% chance that the offspring will have white fur. All of the
offspring are heterozygous (Bb), and black fur (B) is dominant, so only
black fur shows up.
All of the offspring have the black fur phenotype. (Their genotype is Bb).
If grasshoppers have 24 chromosomes in each body cell, then their sex cells have
12 chromosomes. Each sex cell has half the number of chromosomes as a body cell
so that when they combine to make an offspring, the offspring has the right
number of chromosomes.
Explain how a Punnett square models sexual
reproduction.
A Punnett square shows the possible combination of alleles from
sperm and egg. The possible combinations for the offspring are
shown inside of the Punnett square.
8
Describe the relationship between DNA, genes
and chromosomes.
DNA makes up genes, and genes make up chromosomes.
9
10
Use the figure in #9. Describe the functions of
(1) DNA, (2) genes and (3) chromosomes?
1. DNA is a molecule that makes up the code for traits for all living
things.
2. Each gene is a segment of DNA that codes for a particular trait.
3. Chromosomes are structures that hold the genes.
Chromosomes stay in the nucleus of the cell of eukaryotes.
11
Where in the cell are the chromosomes located?
1.
12
What are the three possible effects of
mutations?
Mutations can be helpful; helpful mutations help an organism to survive
and/or reproduce.
2. Mutations can be harmful; these hurt an organism’s chance of survival and/or
reproduction.
3. Neutral mutations neither help nor hurt an organism’s chances.
True or false? If it is false, change the underlined word to make the sentence true.
13
Heredity is the process by which traits are passed from parents to offspring.
TRUE, and genetics is the scientific study of heredity.
True or false? If it is false, change the underlined word to make the sentence true.
14
15
An organism’s physical appearance is its genotype.
FALSE: An organism’s physical appearance is its phenotype. An organism’s pair of alleles for a particular trait is
its genotype
Corn has been selectively bred for many
Corn has been selectively bred to create larger cobs, sweeter
generations.
kernels, more kernels per cob, to resist diseases and pests, and for
Name two traits that humans have selectively
many other traits.
bred for in corn.
Potatoes reproduce by budding. Is this an
example of sexual or asexual reproduction?
This is an example of asexual reproduction because there is only one
parent. The cutting has the same DNA as the parent plant—that is
why it is called a clone.
16
17
18
What is the main advantage of sexual
reproduction over asexual reproduction?
What is a genetically modified organism?
In sexual reproduction, each offspring has a different and new combination of
traits from its two parents. This new combination allows each offspring to have a
different chance of survival under different conditions. When the environment
changes, at least some of the offspring are likely to survive.
A genetically modified organism is a living thing that has had its
genes changed by human activity. This can be done through selective
breeding or through genetic engineering.
19
List 2 examples of genetically modified
organisms.
Some GMOs that we went over in class include: Bt corn, golden rice,
spider goats
a. inbreeding
c. DNA fingerprinting
20
Inserting a human gene into a bacterial
chromosome is an example of:
(circle one)
b. selective breeding
d. genetic engineering
Genetic engineering is the process by which scientists change the
genetic makeup of an organism. In this example, scientists take a
gene from one species (humans) and put it into the genome of
another (a bacteria). This is done to create human proteins such as
insulin.