Introduction to Genetics

Mendel studied 7 traits in pea plants. One of the monohybrid crosses he made was between plants with round seeds (R) and plants with wrinkled seeds (r). All of the seeds in the F₁ generation had a round shape.

Next, Mendel allowed the peas in the F₁ generation to self-pollinate, forming the F₂ generation. What describes Mendel's observations and conclusion about the F₂ generation?

• Three fourths of the F₂ plants show the round seed phenotype and carry the dominant allele for roundness.

• One fourth of the F₂ plants show the round seed phenotype and are heterozygous for roundness.

• The F₂ plants are all heterozygous.

• The F₂ plants all have wrinkled seeds, and some carry the allele for round seeds.

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Mendel was a careful researcher who studied the inheritance of certain traits in garden peas. Which research practices did Mendel not use?

• He crossed true-breeding pea plants.

• He allowed eggs to be fertilized only by self-pollination.

• He analyzed his data mathematically.

• He controlled variables by studying one or two traits at a time.

Study the Punnett square shown here. It describes the potential offspring of a cross between two parents.

What phenotypes will be shown by the offspring?

• All offspring will show the recessive phenotype for this trait.

• All offspring will show the dominant phenotype for this trait.

• Half of the offspring will show the dominant phenotype and half will show the recessive phenotype.

• Three fourths of the offspring will show the dominant phenotype and one fourth will show the recessive phenotype.

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A yellow seeded, purple flowered heterozygous plant (YyPp) is crossed with a green seeded, white flower plant (yypp). (Y = yellow seed allele; y = green seed allele; P = purple flower allele; p = white flower allele)

What is the probability that an offspring of this cross produces plants with green seeds and white flowers? Assume the traits assort independently.

• 0

• 0.25

• 0.5

• 0.75

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A gardener crosses a true-breeding tall tomato plant bearing red fruit with a true-breeding dwarf tomato plant with yellow fruit. In tomatoes, tall vine (T) is dominant to dwarf vine (t), and red fruit (R) is dominant to yellow fruit (r). The results are labeled the F₁ generation. Then the gardener allows F₁ plants to reproduce by self-pollination, generating the F₂ generation.

The Punnett square shows the predicted results of the F₂ generation. Some of the entries in the Punnett square are missing.

Which is the LEAST common phenotype in the F₂ generation?

• plants with tall vines and red fruit

• plants with tall vines and yellow fruit

• plants with dwarf vines and red fruit

• plants with dwarf vines and yellow fruit

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A gardener crosses a true-breeding tall tomato plant bearing red fruit with a true-breeding dwarf tomato plant with yellow fruit. In tomatoes, tall vine (T) is dominant to dwarf vine (t), and red fruit (R) is dominant to yellow fruit (r). The results are labeled the F₁ generation. Then the gardener allows F₁ plants to reproduce by self-pollination, generating the F₂ generation.

The Punnett square shows the predicted results of the F₂ generation. Some of the entries in the Punnett square are missing.

What are the expected phenotype ratios in the F₂ generation?

• 9 tall vine/red fruit; 3 tall vine/yellow fruit; 3 dwarf vine/red fruit; 1 dwarf vine/yellow fruit

• 4 tall vine/red fruit; 3 tall vine/yellow fruit; 1 dwarf vine/red fruit

• 2 tall vine/red fruit; 4 tall vine/yellow fruit; 2 dwarf vine/yellow fruit

• 16 tall vine/red fruit; 9 tall vine/yellow fruit; 3 dwarf vine/red fruit; 1 dwarf vine/yellow fruit

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One dog is heterozygous for black fur (Bb), and its mate is homozygous for blonde fur (bb). The Punnett square describes a cross between the two dogs.

What is the expected outcome of the cross?

• All of the offspring are heterozygous black (Bb)

• Three fourths of the offspring are heterozygous black (Bb); one fourth are blonde (bb)

• Half of the offspring are heterozygous black (Bb); half are blonde (bb)

• One fourth of the offspring are heterozygous black (Bb); one fourth are blonde (bb)

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One dog is heterozygous for black fur (Bb), and its mate is homozygous for blonde fur (bb). The Punnett square describes a cross between the two dogs.

The first litter of the two dogs produces 3 puppies that each had black fur. If the dogs have a second litter, what is the probability of one of the puppies having black fur?

• 0%

• 25%

• 75%

• 50%

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When an allele from the father and an allele from the mother are the same.

• homozygous

• heterozygous

• genotype

• phenotype

When an allele from the mother and an allele from the father are different.

• homozygous

• heterozygous

• genotype

• phenotype