BIol 1 - Chapter 23

If a person has two normal copies of the hemoglobin allele, which statements are true?

* The person is homozygous at the hemoglobin locus. * The person is susceptible to malaria.

Which of the following are causes of evolutionary change?

* genetic drift * gene flow * natural selection * mutation

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?

Stabilizing selection (Stabilizing selection causes no change in the average of the population; extreme phenotypes (in this case, large and small babies) become less common)

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift (Modern travel and migration decreases the chances of there being a small, isolated population.)

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase I

Generation-to-generation change in the allele frequencies in a population is _____.

microevolution

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes

The equation for Hardy-Weinberg equilibrium states that at a locus with two alleles, as in this cat population, the three genotypes will occur in specific proportions:

p^2 + 2pq + q^2 = 1

What does the wide variety of different types of animal eyes represent?

the intermediate forms that probably occurred in the common ancestors of today's animals

Genetic drift is a process based on _____.

the role of chance

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Which of the following evolutionary forces could create new genetic information in a population?

Mutation (Mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.)

Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?

SELECTION (Selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations)

Compare sickle cell disease and malaria.

Sickle cell disease and malaria are both potentially lethal diseases. (Though malaria is an infectious disease and sickle cell disease is inherited, both can cause life-threatening conditions.)

In human gamete production there is an average of _____ crossover events per chromosome pair.

2 - 3 (These crossover events increase the genetic variation among gametes)

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. (A reduction in "tallness" alleles is the change expected as a result of this type of selection.)

Different finch species have beaks of different shapes and sizes. What do these beak differences tell us?

Different finch beak shapes are evidence that finch species adapted to different environments over many generations.

Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?

Directional selection (Directional selection drives the average of the population in one direction, in this case, toward longer necks.)

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?

Disruptive selection (Disruptive selection causes both extreme phenotypes (large and small beaks) to be favored over the intermediate phenotypes.)

Which type of selection tends to increase genetic variation?

Disruptive selection (Disruptive selection eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population)x

Which of the following are basic components of the Hardy-Weinberg model?

Frequencies of two alleles in a gene pool before and after many random matings

Which of the following statements is not a part of the Hardy-Weinberg principle?

The genotype frequencies in the offspring generation must add up to two.

A giraffe and a mouse (both mammals) have the same number of vertebrae in their neck and spine. Which of the following accounts for this?

The vertebrae in their neck and spine are homologous because they share a common ancestor.

Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.

The sickle cell allele will decrease in frequency.

In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?

The value of a particular characteristic; characteristics of an organism can include such traits as size and color.

The ease with which humans travel across the globe is likely to increase _____.

gene flow

All the genes in a population are that population's _____.

gene pool (All the alleles of all the genes of a population make up a gene pool)