Download The Principles of Genetics - Milton

The Principles of Genetics
1.
In corn plants, rough seed shape (R) is dominant over smooth seed shape (r) and
yellow seeds (Y) are dominant over white seeds (y). Determine the probable seed
shape and color of the F1 generation of offspring whose parents are heterozygous
for the traits be completing the Punnett square below.
P1 generation
RY
RrYy x
Ry
RrYy
rY
ry
F1 generation
Genotype
Genotypic Ratio
Phenotype
Phenotypic
Ratio
RRYY
RrYy
RrYY
RRYy
RRyy
Rryy
rrYY
rrYy
rryy
2. To simulate the two-factor cross above, select 4 pennies with masking tape
covering both sides. One side of the tape should be capital letters (RRYY), and
the other side should be lower case letters (rryy).
3. Place the 4 pennies in a cup. Shake the cup and toss the pennies onto your table.
Place a tally into the corresponding genotype category in the table below. Toss
the pennies 47 more times for a total of 48 tosses.
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4. Count the tally marks for each phenotypic combination and record these totals in
the appropriate place in the table below.
Phenotypes Genotypes
Number
Number
Toss
Total
Expected
Expected
Results
Number
for 16
for 48
Observed
Offspring
Offspring
Rough,
RRYY
9/16
Yellow
RrYy
Seeds
RRYy
RrYY
Rough,
RRyy
3/16
White Seeds
Rryy
Smooth,
Yellow
Seeds
Smooth,
White Seeds
rrYY
rrYy
3/16
rryy
1/16
Questions
1. When two homozygous plants with contrasting traits are crossed (PPxpp), what
are the expected genotypes for the offspring?
2. What is the expected genotypic ratio for a one-factor cross of two heterozygous
organisms (PpxPp)?
3. What is the expected phenotypic ratio for a one-factor cross of two heterozygous
organisms (PpxPp)?
4. In your simulated two-factor cross with the coins, why might your actual
experimental values have been different from the values you expected?
5. Why is it helpful to conduct a large number of trials when simulating genetic
crosses?
6. How is an understanding of genetics useful to an animal or plant breeder?
7. Is it possible for two organisms to have different phenotypes but the same
genotype? Explain your answer.
8. Is it possible for two organisms to have different genotypes but the same
phenotype? Explain your answer.
9. How could a guinea pig breeder determine whether a rough-coated guinea pi is
homozygous or heterozygous for this trait?
10. In dogs, wire hair is due to a dominant gene W. Two wire-hair dogs were mated
and produced a puppy with smooth hair. What were the genotypes of the two
parent dogs?
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