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Genetics Basics Review
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PART ONE: TERMINOLOGY
Like any other language, the language of genetics consists of symbols and rules for using these
symbols. When a trait being studied shows dominance, it is observed in nature much more
frequently than if it is a recessive form. The capitalized letter of the dominant form becomes
its symbol (ex: R stands for round seeds.) For the recessive form of the same trait (the
recessive allele), the symbol remains the same but is not capitalized (ex: r stands for wrinkled
seeds). Complete the following chart using these rules of symbols.
Dominant
Recessive
Height
Coats
T
(tall)
___
(short)
___
(colored)
c
(white)
Plant Trait
Pods
Seed Color
G
(green)
___
(yellow)
___
(yellow)
y
(green)
Shape
Flower
R
(round)
___
(wrinkled)
___
(axial)
a
(terminal)
1. Using the symbols from the above chart, write the allele symbols that would be present in
the following homozygotes. Next, indicate whether they are going to express the dominant
or recessive trait.
Allele Symbol
Expressed Trait (dom or rec)
a. tall, stemmed plants
b. terminal flowers
c. white seed coats
d. yellow seeds
e. yellow pods
2. Write the symbols for the following heterozygotes.
a. yellow seeded peas
______
d. colored seed coats
______
b. axial flowers
______
e. round seeds
______
c. green podded peas
______
f. tall stemmed plants
______
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3. The following letters represent pairs of alleles. Indicate whether each pair is a
heterozygotes or homozygote. Then indicate whether each pair would display a dominant
or recessive phenotype.
Homo or Hetero
Phenotype (dom or rec)
a. DD
b. ss
c. Tt
d. Dd
4. What percentage of the alleles does each parent contribute to their offspring? _____%
PART TWO: SINGLE TRAIT CROSSES Use gene letters from front side of sheet to
complete the following problems:
5. A plant that is heterozygous for its green pods is crossed with a plant with yellow pods.
a. Show parental cross and punnett square  ___ x ____
b. Genotypic ratios:
c. Phenotypic ratios:
6. If two heterozygous round seeded pea plants are crossed, then:
a. Show parental cross and punnett square  ___ x ____
b. Genotypic Ratios:
c. Phenotypic Ratios:
7. If a homozygous axial flowered plant is crossed with a terminal flowered plant, then:
a. Show parental cross and punnett square  ___ x ____
b. Genotypic Ratios:
c. Phenotypic Ratios:
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