AP Biology : Evolution and Genetics

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #3 : Draw And Interpret Phylogenetic Trees

Cladograms provide what information?

Possible Answers:

All of these

The geographic distribution of a species

Pedigrees of many generations of a species

Evolutionary relatedness among organisms

Characteristics of certain animals

Correct answer:

Evolutionary relatedness among organisms

Explanation:

Cladograms show evolutionary relatedness, usually based on the similarity of the DNA sequences between different species. The closer two branches of the cladogram are to each other, the more closely related the organisms are to each other. The ends of the branches indicate a common ancestor shared by all of the species of that branch. Cladograms do not show geographic relationships. Although primitive cladograms were formulated based on physical characteristics of animals, now, DNA analysis provides a much more accurate comparison between species. Furthermore, cladograms are not limited to animals.

Example Question #4 : Draw And Interpret Phylogenetic Trees

Vt_phylo_pic_1

From the diagram above, to which species is species C most closely related?

Possible Answers:

D only

All of the given species are equally related

A and B

D and E

Correct answer:

A and B

Explanation:

Each branch in the tree represents a break from the common ancestor at the bottom. A and B are both branches off of the same larger branch that C is also a branch of. D, E and F branched off from the common ancestor earlier than A, B, or C. In general, branches that are closer together, and are on the same larger branch, represent organisms which are closely related.

Example Question #301 : Evolution And Genetics

Two species sharing the same __________ will be the most closely related

Possible Answers:

phylum

order

kingdom

class

family

Correct answer:

family

Explanation:

In the system of biological classification, organisms are classified in a hierarchy, or taxonomy. The highest levels of classification are the most inclusive, while the lower levels become more and more specific until a single species is identified. From most inclusive to least inclusive, organisms are assigned a kingdom, a phylum, a class, an order, a family, a genus, and finally a species.

Organisms sharing the same classification at less inclusive levels will be more closely related. For example, two organisms sharing the same genus will be more closely related than those who only share the same family. Of the given answer choices, family is the most specific level of classification.

Example Question #1 : Draw And Interpret Phylogenetic Trees

Which of the following types of data are used to generate phylogenetic trees?

Possible Answers:

Molecular sequencing data

Neither molecular sequencing data nor morphological similarities

Both molecular sequencing data and morphological similarities

Morphological similarities

Correct answer:

Both molecular sequencing data and morphological similarities

Explanation:

Phylogenetics is the study of relationships between organisms and groups of organisms. This is done through the production of phylogenetic trees, which are used to describe these relationships. To make phylogenetic trees, scientists use molecular sequencing and/or morphological similarities in order to characterize the relationships between organisms.

Example Question #301 : Evolution And Genetics

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According to the character table above, which of the following would define a clade?

Possible Answers:

Sea urchin, jellyfish

Lion, fish, sea urchin

Fish, sea urchin

Scorpion, sea urchin

Fish, sea urchin, scorpion

Correct answer:

Lion, fish, sea urchin

Explanation:

A clade is defined by a organisms that possess a shared derived trait. In other words, we need to find a set of organisms in the table that includes all organisms with a certain listed trait, while excluding any that lack that specific trait. The lion, fish, and sea urchin are the only clade listed. They are all triploblastic, segmented deuterostomes, and none of the other species share those characteristics. The trait of being a deuterostome is the shared derived trait that defines this clade.

Sea urchin, jellyfish: The jellyfish is the outgroup of the tree presented in the table, as it does not have any of the listed traits. Its last common ancestor with the sea urchin is also its last common ancestor with all of the other species, so a clade with the jellyfish must include all 5 species in the table.

Fish, sea urchin, scorpion: All share segmentation and three tissue layers, which the jellyfish does not have. However, the lion also has segmentation and three tissue layers, so it must be included to form a clade.

Fish, sea urchin: Both are deuterostomes with segmentation and three tissue layers, but the lion is also a deuterostome, so it must be part of the clade.

Scorpion, sea urchin: They both have segmentation and three tissue layers, but so do the lion and the fish, so they must also be part of the clade.

Example Question #1 : Understand Co Dominance

A mother with type A blood and a father with type B blood have a child. What blood type is impossible for that child to have?

Possible Answers:

AB

B

O

All are possible

A

Correct answer:

All are possible

Explanation:

The mother's possible genotypes for blood are AO and AA, while the father's are BO and BB; therefore, the child could have any blood type because we could receive an O allele from either parent.

The full possibilities are:

A from mother, O from father - blood type A

A from mother, B from father - blood type AB

O from mother, B from father - blood type B

O from mother, O from father - blood type O

Example Question #1 : Understand Co Dominance

In a specific type of flower the genes coding for color display codominance. What would you expect the phenotype to be for a cross between a flower homozygous for white coloration and a flower homozygous for red coloration?

Possible Answers:

Distinct red and white spots

Pink

Red

White

Correct answer:

Distinct red and white spots

Explanation:

Codominance is a phenomenon in which the phenotypes associated with both alleles will be expressed in their entirety. This expression pattern results in mottled expression, creating distinct red and white spots for the flower. This is different than incomplete dominance, in which the two phenotypes appear to blend together.

Example Question #3 : Understand Co Dominance

In humans, blood type is determined by three alleles: A, B, and O. Both the A and B alleles are dominant to the O allele. When both A and B are present, however, a combined phenotype of AB results. In AB individuals, both A and B antigens are fully expressed on the cell surface. This is an example of __________.

Possible Answers:

incomplete dominance

codominance

complete dominance

nondominance

Mendelian dominance

Correct answer:

codominance

Explanation:

Since the A and B alleles both seem to exert a form of dominance, this is clearly not our common example of a complete dominance scenario. We can conclude that blood type is determined by either incomplete dominance or codominance.

In incomplete dominance, both alleles exert influence to a lesser degree resulting in a "blended" phenotype. In blood type, both alleles exert their full influence together. Instead of yielding a blended phenotype, this situation results in a phenotype that is functionally equivalent to having both A and B blood types at once. The A and B alleles are codominant.

Example Question #4 : Understand Co Dominance

Scientists are trying to figure out the dominance hierarchy for a newly discovered plant. They have found that when a true-breeding yellow plant is crossed to a true-breeding green plant, the resulting offspring have distinct spots of yellow and green. What is the most likely explanation for this result?

Possible Answers:

Codominance

Incomplete dominance

Yellow is the dominant allele

Green is the dominant allele

Correct answer:

Codominance

Explanation:

In the resulting offspring, both phenotypes are displayed equally. This is a classic example of codominance. If an intermediate phenotype was observed, incomplete dominance would be the correct answer.

In codominance, both alleles are considered dominant. This means that both alleles will be fully expressed in different regions, resulting in spots. In incomplete dominance neither allele is fully dominant, so both can be expressed simultaneously in a given area. The result is a blending of both alleles.

Example Question #1 : Understand Co Dominance

The shorthorn cattle coat color exhibits codominance. If a homozygous red individual and homozygous white individual produce an offspring, what will the resulting coat color be?

Possible Answers:

White

Pink

Red

Roan

Correct answer:

Roan

Explanation:

In cases of codominance, the offspring have both alleles expressed at the same time. Thus, the coat color will be roa, which contains both white and red hair.

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