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AP: Chapter 14A
Mendel and the Gene Idea
1. How does the “blending hypothesis” differ from the “particulate hypothesis” for the transmission of traits?
2. List 3 of the advantages of Mendel’s choice of the garden pea as a model organism.
3. Use the diagram below to label the generations: P, F1, F2, pure, hybrid and complete the punnett squares for
each of the crosses.
4. Define the Law of Segregation.
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5. During what phase does segregation of alleles occur?
6. What is the difference between an allele, a gene, and a locus?
a. allele
b. gene
c. locus
7. Briefly define the following terms:
a. Homozygous
b. Heterozygous
c. Phenotype
d. Genotype
8. What is the purpose of a test cross?
9. Indicate the phenotypic ratios that result in the F2 from the F1 cross (dihybrid cross)
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10. In humans the allele for albinism (a) is recessive to the allele for normal skin (A) pigmentation. If 2
heterozygotes have children, what is the chance that a child will have normal skin pigment? What is the
chance that a child will be albino?
Normal pigment
Albino
a. If the child is normal, what is the chance that it is a carrier (heterozygous) for the albino allele?
11. In purple people eaters, one-horn (H) is dominant and no horns (h) is recessive. Show the cross of a purple
people eater that is heterozygous for horns with a purple people eater that does not have horns. What
would be the frequency of each genotype and phenotype be?
Phenotype
Genotype
12. In humans, the brown-eye (B) allele is dominant to the blue-eye (b). If two heterozygotes mate, what will
be the likely genotype and phenotype ratios of the offspring?
Phenotype
Genotype
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13. In pea plants, the green color allele (G) is dominant over the yellow color allele (g) for seed color and tall
(T) is the dominant allele in plant height. Parents heterozygous for both traits are cross-pollinated. Using
the punnett square below, determine the frequency for the four different phenotypes of the offspring.
Tall plant, Green seeds
Tall plant, yellow seeds
Short plant, green seeds
Short plant, yellow seeds
14. Now let’s try a shortcut way of solving that same dihybrid cross. Because of Mendel’s Law of Independent
assortment, you can work with the color gene and the height gene separately… so set up 2 separate
monohybrid crosses from those same parents:
Now use the laws of probability to calculate your frequencies of each trait alone and combined:
height
color
height
= freq.
Tall plant, green seed
Short plant, green seeds
Tall plant, yellow seeds
Short plant, yellow seeds
color
= freq.
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15. Use the rules of probability to determine the expected ratio of offspring showing two recessive traits in the
trihybrid cross (EeAabb X Eeaabb).
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