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BIOLOGY
Worksheet: Unit 3 Review
1. Define the following terms:
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Homozygousheterozygous true breedinggenotypephenotypenon-disjunctionco-dominanceincomplete dominancelinked genesgenetic engineeringcloning-
Homozygous- two of the same allele (i.e. EE or
ee)
Heterozygous- Two different alleles (i.e. Ee or
Ss)
True-breeding- Means the same thing as purebred. Will always produce the same
offspring.
Genotype- The “letter” combination. Describes
the two alleles an organism has (i.e. EE, Ee,
ee)
Phenotype- The physical characteristic that
results from a gene (i.e. Tall or short, Red or
white)
Non-disjunction- When chromosomes do not
separate during meiosis. Results in gametes
with extra or too few chromosomes
Example: would result in Down Syndrome,
Klinefelters Syndrome, Turner’s Syndrome)
Co-dominance- Both alleles are dominant and
both expressed in offspring.
(i.e. Red and White hair are dominant in cattle. A
purebred red is crossed with a purebred white
cow and results in a cow that is roan in colorhas both red and white hair)
Incomplete dominance- Neither allele is
dominant.
red flower crossed with white flower and produces
pink flowers in offspring
Linked genes- Genes that are located on the
same chromsome. Usually inherited
together- they’re “linked”
Genetic engineering- changing of an organisms
DNA to give new trait
Cloning- creating a genetically identical copy of
gene or of an organism
2. What do you call the process where two gametes
fuse?
Fertilization
3. What is the name of the cell that is formed as a
result of this fusion?
Zygote
4. What is crossing-over (what process does it
occur in, and what is the result of this process)?
When chromosomes cross over each other
during meiosis and exchange bits and pieces
of themselves
5. Describe the process of DNA replication. (where
does it occur and what is the result)
DNA making copy of DNA. Occurs in nucleus
of cell. Requires certain enzymes to catalyze
reaction.
6. Complete the chart below comparing DNA and
RNA:
DNA
RNA
Type of sugar
Deoxyribose
Ribose
Nitrogen base
A,T,C,G
A,U,C,G
Complimentary
bases
Double or Single
stranded?
A-T
C-G
Double
A-U
C-G
Single
7. Blood type is determined by multiple alleles.
Complete the chart below showing possible
genotypes and phenotypes of blood type (page
205)
Phenotype
Genotype
Type A
IA IA , IA i
Type B
I B I B , IB i
Type AB
IA IB
Type O
ii
8. A human karotype shows 22 pairs of
autosomes, and one pair of sex chromosomes.
9. A male has the genotype XY and a female has
the genotype XX
10.In the process of transcription a DNA sequence
reads CATTGA, what would the complementary
mRNA strand that would read?
CATTGA
GUAACU
11. The genes on DNA contain instructions to
assemble proteins
12.The monomers of proteins are amino acids
13. Three nitrogen bases make up a codon for an
amino acid.
14.State Mendel’s principles of genetics.
a. What is the Principle of Dominance?
Some alleles are dominant and some are
recessive
b. What is the Law of Independence Assortment?
allele pairs separate independently of each
other during meiosis
15.Be able to use the genetic code chart. What are
the amino acids coded for with the following
codons?
a. UUUb. UUCc. ACGd. CCUe. AUU-
f. AAAg. GUCh. GCC-
15.Be able to use the genetic code chart. What are
the amino acids coded for with the following
codons?
a. UUU- Phe
b. UUC- Phe
c. ACG- Thr
d. CCU- Pro
e. AUU- Ile
f. AAA- Lys
g. GUC- Val
h. GCC- Ala
16.Summarize the process of translation; (where
does it occur and what is the result. Include the
three types of RNA involved)
RNA making Proteins. Occurs in the cytoplasm
on the ribosomes. Involves all three types of
RNA (mRNA, tRNA, and rRNA)
17. What did Mendel call the “factors” that
determine traits?
Genes
18.What organisms do Mendel’s principles apply
to?
All living things
19.What causes mutations in DNA?
a. Are all genetic mutations expressed? Explain
No. May not affect phenotype. May not change
protein produced. May occur in non-coding
part of DNA
b. What created oil-eating bacteria?
Induced mutations (radiation)
20.What is the purpose of Punnett squares?
A tool to predict the possible offspring of a
genetic cross
21.State the phenotypic ratio of a heterozygous
dihybrid cross?
9:3:3:1
22. Why would a scientist or breeder use selective
breeding?
To try and combine certain traits in offspring to
produce desired results
23. What is inbreeding and how does it occur?
Inbreeding is when two closely related
organisms are crossed. Increases the
chances that recessive alleles will combine in
offspring
24. Skin color in humans is a result of Polygenic
inheritance.
25. What are the possible gametes produced by
the parent genotypes below?
a. RrYy- RY, Ry, rY, ry
b. rrYY- rY only
c. SSDD- SD only
26. Colorblindness is a sex-linked trait. Why do
males exhibit colorblindness more than females?
Because the genes are carried on the X
chromosome and males only have one X
chromosome. If they have the recessive
allele they will have the disorder
27. Complete the following table comparing Mitosis
to Meiosis:
MITOSIS
MEIOSIS
2
4
Diploid
Haploid
Asexual
Sexual
Results in body cells
or sex cells
Body cells
Sex cells
Number of divisions
involved (one or two)
One
Two
Number of cells
produced
Haploid or diploid
cells produced
Involved in asexual or
sexual reproduction
28. Complete the chart below comparing the
process of Replication, Transcription and
Translation.
Where does it
occur?
___ making ___
What molecules
are involved in
the process?
(DNA, mRNA,
tRNA, rRNA)
Replication
Nucleus
Transcription
Nucleus
Translation
Cytoplasm
DNA making
DNA
DNA
DNA making
RNA
DNA and
RNA (mRNA,
tRNA, rRNA)
RNA making
Proteins
RNA
(mRNA,
tRNA, rRNA)