Mendel's Work and Principles

Mendel studied seven traits in pea plants. One of the monohybrid crosses he made was between plants with round seeds and plants with wrinkled seeds. What was a conclusion Mendel drew from the F₁ generation of this cross?

• The dominant factor, or allele, is for round seeds.

• The dominant factor, or allele, is for wrinkled seeds.

• The factors or alleles for round seeds disappear completely from the plants.

• The factors or alleles for wrinkled seeds disappear completely from the plants.

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A geneticist crossed pure breeding black mice (BB) with pure breeding brown mice (bb). All the mice in the F₁ generation had black coats. When these mice were crossed, they yielded 961 black-coated mice and 317 brown-coated mice. The Punnett square describes this cross. The numbers 1 to 4 are shown instead of the genotypes for the offspring. Which of the genotypes, if any, is MOST likely to occur in the F₂ generation?

• BB

• Bb

• bb

• All are equallly likely.

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A geneticist crossed pure breeding black mice with pure breeding brown mice. All the 992 mice in the F₁ generation had black coats. When these mice were crossed, they yielded 961 black coated mice and 317 brown coated mice (a ratio of 3:1).

How could you account for the ratio of black coated to brown coated mice in the F₂ generation? Select all that apply.

• The F₁ male produced two kinds of sperm, half carrying an allele for black coat color, and half carrying an allele for brown coat color.

• The F₁ female produced two kinds of eggs, half carrying an allele for black coat color, and half carrying an allele for brown coat color.

• An approximately three-to-one ratio of black to brown coated mice in F₂ is accounted for by the black allele being dominant over the brown allele.

• The brown allele is not independent from the black allele and disappears in the F₁ generation.

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A geneticist crossed homozygous, dominant green pod color pea plants (GG) with homozygous recessive yellow pod color pea plants (gg). All the plants in the F₁ generation had green pods.

What ratio of green pod color plants to yellow pod color plants would you predict when you cross a green pod color F₁ plant with a yellow pod color plant?

• Three-quarters of the plants will have a green pod color and one quarter will have a yellow pod color.

• All of the plants will have a green pod color.

• Half of the plants will have a green pod color, and half of the plants will have a yellow pod color.

• All of the plants will have a yellow pod color.

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The diagram is a model of the genes for two pea plants: a tall plant and a short plant. For the model to accurately describe the genotype of the gametes, what letters should be entered into the four empty boxes? Assume the letters in the answer choices are entered into the boxes from left to right.

• TT, TT, tt, tt

• Tt, Tt, Tt, Tt

• T, T, t, t

• T, t, T, t

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In a cross of purple flowered heterozygous plants (Pp), the letter P represents the allele for purple flowers and the letter p represents the allele for white flowers. What is the probability that an offspring of this cross expresses plants with purple flower phenotypes?

• 0

• 1/4

• 1/2

• 3/4

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In pea plants, height is determined by an allele for tallness (T) that is dominant over an allele for shortness (t). What is the probability that a gamete, selected at random, would carry the short allele in a cross of heterozygous tall pea plants (Tt x Tt)? HINT: How many t's are there amongst the Punnett square?

• 1/8

• 1/4

• 1/2

• 3/4

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Study the Punnett square, which shows a dihybrid cross of round, yellow peas. (RrYy x RrYy). If all 16 genotypes shown in the Punnett square are equally likely, which statement can be concluded?

• The gene for pea shape expresses incomplete dominance over the gene for pea color.

• The gene for pea shape is codominant with the gene for pea color.

• The gene for pea shape is linked to the gene for pea color.

• The gene for pea shape sorts independently of the gene for pea color.

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In a certain plant, the allele for red flower color (R) is dominant over the allele for white flower color (r). A cross is performed between a plant with red flowers and a plant with white flowers. The offspring are 47 plants with red flowers and 51 plants with white flowers. What are the genotypes of the parent plants?

• Rr and rr

• Both are Rr

• It cannot be determined

• RR and rr

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In horses, black coat (B) is dominant over brown coat (b) and trotter (T) is dominant over the recessive allele pacer (t). A dihybrid cross is conducted for these two traits. Which combination of traits is likely to appear in the offspring with a probability of 1/16?

• black coat, trotter

• black coat, pacer

• brown coat, trotter

• brown coat, pacer

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