Biology 2 Exam 1

What items reflect a phenotype related to -globin, a subunit of hemoglobin in humans?

• sickle cell anemia

• susceptibility to malaria

• sickle cell shaped blood cells

An individual is heterozygous for a gene if:

he or she developed from a sperm and egg that carried different alleles

The A, S, and C alleles of the f-globin gene differ in a single nucleotide that changes____ which has a dramatic effect on___

Hint: Review Figure 13.3.

one amino acid; protein function

If you determined that a plant with red flowers carried alleles for both red flowers and white flowers, you would say that this plant has a red ____and it has a red and white _____

phenotype; genotype

The observable characteristics of an organism are its ____ whereas the genetic makeup of the organism is its _____

phenotype; genotype

A phenotype always refers to something that you can see with your eyes, like hair color or eye color.

false

While a mutation will not always change the phenotype of an individual, it will always change the genotype.

true

If an individual is homozygous for a certain allele, it means that:

the individual received the same allele from each parent.

Phenotypes:

can be influenced by environmental conditions.

Alleles are alternative molecular forms of a gene.

true

An organism that has two different alleles of a given gene has a(n) _____ genotype.

heterozygous

The observable characteristics of an organism constitute its genotype.

false

An individual is homozygous for a gene if:

they developed from a sperm and an egg that carried the same allele.

If a population has only one allelic form of the gene, every individual is:

homozygous.

Mutations that affect only the individual in which they occur are called ____ mutations; ___ mutations are passed from parent to offspring

somatic; germ-line

Which circled region contains two identical pieces of double-stranded DNA?

C

The chromosomes in the circled region could both be chromosomes from the same parent.

False

Environmental factors are unlikely to affect variable expressivity in humans.

false

Each human gene only has two different alleles—one mutant allele and one "normal" allele.

false

Mutations in skin cells that are non-heritable are ___ mutations, whereas mutations that can be passed on from parent to offspring are referred

somatic; germline

In a fish species, the eggs tend to be fertilized more often by the mid-sized males and less often by the largest and smallest males. This is an example of:

stabilizing selection

A cattle breeder selects the largest males for breeding with the largest females. This is an example of:

directional selection

Female starlings (birds) that lay clutches of four or five eggs have more surviving young than those with either larger or smaller clutches. This is an example of:

stabilizing selection

On Island X, the plant population contains only two species. One plant species produces only very large seeds, and the other produces only small seeds. There is only one species of bird on the island, and the birds use these seeds as their only food source. Currently, there is a wide range of beak sizes within the population of birds as shown in the diagram.

Small-beaked birds are better able to consume the smaller seeds, while large-beaked birds are better at consuming the larger seeds. Birds with intermediate beak size can make use of both seed sizes.

A disease is introduced to the island, which kills only the plants that produce the large seeds. Consider changes in the bird population following the death of all plants that produce large seeds. Which portion(s) of the finch population will be selected against and least likely to have their genes represented in the next generations?

portion C only

What type of selection occurs when an environmental condition-for example, food source characteristicscauses selection toward one extreme of a trait's range of variation?

directional

As their only food source, the birds find the plant seeds quite delectable. However, while small-beaked birds do very well consuming the smaller seeds, and large-beaked birds thrive on the larger seeds, birds with intermediate beak size are not good at consuming either size seed, and they struggle to get sufficient nutrition. What type of selection might we predict over the course of multiple generations of these birds?

disruptive

Steps in natural selection

1. mutation - mutation occurs

2. recombination- recombination creates new genetic combinations

3. competition- individuals in a population compete for limited resources

4. fitness - some variants survive and reproduce more than others in a particular environment

5. inheritance - the variants that survive and reproduce more than others contribute disproportionately to the next generation

6. adaptation- the population becomes more fit over time

Speciation occurs when:

two populations become reproductively isolated from one another.

A deleterious mutation:

decreases survival and/or reproduction.

At which point are the frequencies of genotypes AA and aa equal?

point c

Refer to the data in the table to determine which statement describes what happened between generations 1 and 4 of this fish population.

An influx of fish with medium fin size entered the population.

Which type of mutation does not undergo natural selection in a population?

neutral

Which allele underwent negative selection?

allele d

Which scenario(s) depict allopatric speciation in process? Select all that apply.

• Humans set up a dam in the middle of a river, splitting a fish population in two. The two resulting fish populations accumulate different sets of mutations over time.

• A small portion of the population on the mainland moves to an island. Over time, the island population genetically diverges from the mainland population.

Which mechanism is responsible for the changes in fish size between generation 1 and generation 100?

directional selection

Within a species, there is a given trait determined by two alleles. The allele frequencies for these two alleles are represented by p and q.

If Hardy-Weinberg conditions are met, which is not a possible genotype frequency?

p² q²

A neutral mutation:

does not affect survival or reproduction.

Which type of mutation is most likely to undergo genetic drift in a population?

neutral

At which point is 100% of the population exhibiting the recessive phenotype?

point a

When a mutation is fixed in a population, what percentage of individuals have this mutation?

100%

Consider several species with varying population sizes. In which population are the effects of genetic drift most extreme?

population size = 4

which allow becomes fixed in the population

allele a

refer to the data on the table to calculate the allele and genotype frequencies

p = 0.70 q = 0.30; p² = 0.49 2pq = 0.42 q² = 0.09

Why is each individual (except the African HIV strain) in the HIV phylogeny represented by two sequences, not just one?

HIV evolves rapidly within a patient, so it is important to sample the range of sequence variation present in each patient.

Why is the top part of the HIV phylogeny tree colored red?

The red sequences are the sequences that are phylogenetically derived from the common ancestor of the dentist's sequences.

In this analysis, HIVELI is:

an out group

Is there a significant difference between the original

HIV phylogeny (shown in the How Do We Know? figure) and that shown in Figure 1?

No, because the basic topology - the order of the nodes - is the same in both the prosecution and defense presentations.

Which node on the tree in Figure 2 represents the most recent common ancestor of the dentist's two sequences?

c

Why are the C-1 and C-2 sequences in the HIV phylogeny linked by much shorter branches than the B-1 and B-2 ones?

Because was infected more recently than B.

In a court case on the origin of HIV infection in the dental patients, the defense argued that the group in red consists of people of similar ancestry (all European Americans) whereas the group in black consists of people of different ancestries (African Americans, Asians, and European Americans), meaning that those different ancestries are expected to cluster together on a phylogenetic tree, regardless of the dentist's activities.

No, the phylogeny is of HIV sequences, and is independent of the ancestry of the people involved.

Why are all the sequences - black (except HIVELI) and red more closely related to each other than to HIVELI?

Because HIV first arose in Africa; all the non-African sequences in this sample are likely derived from a single (or a few ancestral strain(s) that entered North America from Africa.

What does this observation suggest about the origin of HIV?

that humans were somehow - probably through the processing of tainted bush meat - infected from both primate species