QUESTION: 577 Topic Exam C: Section 3 (science)

Background Information

If a characteristic is expressed in an organism, that is the organism's phenotype. The genes that determine that phenotype are called the organism's genotype. A characteristic is determined by the organism's genes that were passed down by the parents. If a gene is dominant, that gene will be expressed in the phenotype. If a gene is recessive, it will only be expressed in the phenotype when two recessives are present in the genetic makeup of that organism.

Description

A cat breeder is losing money because customers are buying cats that do not have white paws, and the cat breeder has mostly white-pawed cats. She decides to experiment with breeding with the six remaining cats that do not have white paws to see if she can produce litters of kittens without white paws. A cat without white paws can be either pure for the non-white pawed cats (homozygote) or a carrier for white paws (heterozygote). The trait for having white paws is recessive.

A homozygote for the non-white = WW (non-white cat paws).
A heterozygote for white = Ww (non-white cat paws).
A homozygote for the white = ww (white cat paws).

You can create Punnett Squares to show the phenotypes that would result from two parent cats breeding.

WW × WW cross yields all non-white pawed kittens.

WW × Ww cross yields all non-white pawed kittens in the first generation; however, 1/2 will be carriers for white paws.

Ww × Ww cross yields a ratio of 1 homozygote non-white paws to 2 heterozygote to 1 homozygote white paws for the first generation.

Experiment

Group 1
The cat breeder breeds two cats that do not have white paws. She finds that the first generation of kittens in this group does not have any white paws. When the first generation of cats was bred, she finds that the second generation of these kittens is 1/8 white-pawed and 7/8 not white-pawed.

Group 2
The cat breeder breeds two different cats that do not have white paws. She finds that the first, second, and third generations of kittens in this group did not have any white paws.

Group 3
The cat breeder breeds two different cats that do not have white paws. She finds that the first generation of kittens in this group has 1/4 with white paws and 3/4 without white paws. She does not breed for a second generation in this group.

If a gene is recessive:

it will only be expressed in the phenotype when two recessives are present in the genetic makeup of that organism.
it will never be expressed in the phenotype.
it will only be expressed in the phenotype when a dominant and a recessive gene is present in the genetic makeup of that organism.
it will always be expressed in the phenotype.

Answer(s): A

Explanation:

According to the Background Information in the passage, if a gene is recessive, it will only be expressed in the phenotype when two recessives are present in the genetic makeup of that organism.

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QUESTION: 578 Topic Exam C: Section 3 (science)

Answer(s): B

Explanation:

There is one parent in Group 1, two in Group 2, and none in Group 3 who are pure for not having white paws.

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QUESTION: 579 Topic Exam C: Section 3 (science)

Cats from groups 2 and 3 should be switched between the groups to produce kittens with no white paws.
Cats from groups 1 and 3 when switched would produce all white-pawed cats for all generations.
Cats from groups 1 and 2 should be switched to produce a greater number of white-pawed cats than the original setup.
The cat breeder should not make any changes because a greater number of cats without white paws cannot exist.

Answer(s): D

Explanation:

The cat breeder was very lucky to originally put the two cats together (male and female) who were pure for not having white paws. Any other combination of the six original cats would have produced a lesser number of kittens that are genotypic ally pure for not having white paws.

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QUESTION: 580 Topic Exam C: Section 3 (science)

the fact that some people like white-pawed cats.
not all of the cats being fed the same brand of cat food.
a cat from Group 3 breeding with a cat from Group 2 during the experiment.
the parents in Group 1 breeding 1 month later than the cats in Groups 2 and 3.

Answer(s): C

Explanation:

The experiment would not be affected by people's preference in cats, nor would it depend on the food the cats eat. You might think that if the cats from Group 1 bred one month later than the other cats it would affect the outcome; however, the difference in time will not change the genetic makeup of the cats. Therefore, the outcome would be affected by cats from different groups being bred together.

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QUESTION: 577 Topic Exam C: Section 3 (science)

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QUESTION: 578 Topic Exam C: Section 3 (science)

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QUESTION: 579 Topic Exam C: Section 3 (science)

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QUESTION: 580 Topic Exam C: Section 3 (science)

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