Genetics Review Sheet
Answers
1.Define the following genetics terms
on a separate sheet of paper.
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Genetics
Heredity
Chromosome
Gene
Allele
Trait
Dominant
Recessive
Genotype
Phenotype
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Homozygous
Heterozygous
Purebred
Hybrid
Punnett Square
Codominance
Incomplete dominance
Mutation
Vocabulary
• genetics – the science of how traits are inherited
through alleles passes from one generation to
another
• heredity – passing of traits from parent to
offspring
• chromosome – threadlike strands of DNA and
protein in a cell nucleus that carry the code for
the cell characteristics of an organism
Vocabulary
• gene – the segment of DNA on a chromosome
that directs the making of a specific protein,
thus controlling traits that are passed to
offspring
• allele – a different form a gene may have for a
trait
• trait –another name for a characteristic
Vocabulary
• dominant – the form of a trait that appears to
dominate or mask another form of the same trait
• recessive – the form of a trait that seems to disappear
in a population but can reappear depending on the
way the alleles combine
• genotype – the genetic makeup of an organism
• phenotype – a physical trait that shows as a result of
an organism’s particular genotype
Vocabulary
• homozygous – an organism that has two identical
alleles for a trait
• heterozygous – an organism that has two different
alleles for a trait
• purebred – an organism that always produces the
same traits in it’s offspring
• hybrid – an organism that produces different traits in
it’s offspring
Vocabulary
• Punnett square – a tool that shows how genes can
combine; used to predict the probability of types of
offspring
• codominance – the production of a phenotype in an
offspring that has both dominant and recessive traits
shown in a heterozygous offspring
• Incomplete dominance– the production of a phenotype in
an offspring that is a combination or mix of the dominant
and recessive traits shown in a heterozygous offspring
• mutation – any permanent change in an organism’s genetic
material
2. What are the 3 parts of the DNA
molecule?
• Sugar
• Phosphate
• Nitrogen base
3. Nucleotides are the building blocks
of DNA, what makes up a nucleotide?
• 1 sugar + 1 phosphate + 1 nitrogen base
4. What are the 4 types of nitrogenous
bases in DNA?
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A (Adenine)
C (Cytosine)
G (Guanine)
T (Thymine)
5. What is the base-pairing rule?
• A pairs with T
• C pairs with G
6. List 3 examples of genetic traits
(traits that can be passed from parent to offspring).
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Natural hair color
Eye color
Hitchhikers thumb
Height
Cleft chin
7. List 3 examples of traits that are
NOT genetic.
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Dyed hair color
Personality
Having a broken arm
Hair length
Intelligence
8. Blue eyes are recessive and brown eyes are
dominant; write all possible genotypes for:
• A blue eyed individual? bb
• A brown eyed individual?
BB or Bb
9. Why are genotypes written with two
letters? (Why is one letter not enough?)
• A genotype has two letters because one letter
is the allele from the mom and the other
letter is the allele from the dad
Genotypes
• 10. What is the genotype for a homozygous
dominant individual?
HH
• 11. What is the genotype for heterozygous
dominant individual?
Hh
• 12. What is the genotype for a homozygous
recessive individual?
hh
13. Can an organism be heterozygous recessive
for a trait? Explain why or why not?
• No, the only way an organism can be recessive
for a trait is if both alleles (letters) are
lowercase. If there is at least one dominant
allele (capital letter) then the trait is dominant
NOT recessive.
14. The example of eye color is a “normal”
dominant/recessive situation. How is incomplete
dominance or codominance different from a
normal dominant/recessive situation? Use an
example from the alien lab in your answer.
• In “normal” dominance there is 2 possible
phenotypes for the trait
– HH and Hh = dominant, hh = recessive
• In incomplete or codominance there is 3 possible
phenotypes for the trait
– HH = dominant, hh = recessive,
– Hh = codominant or incomplete dominance
15. A blue eyed father and a heterozygous
brown eyed mother wanted to know what color
eyes their children might have.
• Genotype for father =
• Genotype for mother =
ee
Ee
Complete the punnett square
Punnett Square
E
e
Possible offspring genotypes:
e
Ee
ee
Ee-2
ee-2
e
Ee
ee
Possible offspring phenotypes:
Brown eyes-2
Blue eyes-2
16. Is the trait for curly tail dominant
or recessive? How do you know?
Male with curly tail
Male without curly tail
Female with curly tail
Female without curly tail
Dominant-In the F3 generation all of the
children had curly tails even though the
dad has no curly tail…the mom’s curly tail
“covered up” or was dominant to not
having a curly tail
17. What are the genotypes of the
parents in the P1 generation?
Male with curly tail
Male without curly tail
Female with curly tail
Female without curly tail
• Male = hh because he does not have a curly tail
(he is recessive)
• Female= Hh because there is a female offspring
without a curly tail, the female in P1 had to be
able to give the female offspring in F1 “h”
• 18. Know and be able to answer the following
questions about a genetic disorder. How
would you describe the disorder? What is its
cause? What are 2 symptoms of the disorder?
What are 2 other facts about the disorder?
(ex: treatments, cures)