MB - Ch 23

gene flow

-A result of the movement of fertile individuals or their gametes -can introduce new alleles into a population's gene pool

genetic drift

-Causes allele frequencies to fluctuate randomly -Responsible for the found effect -Responsible for the bottleneck effect

natural selection

-Consistently causes a population to become better adapted to its environment -A result of differential success in reproduction -Cannot cause a harmful allele to become more common

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

2-3

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

genetic drift

Fill in the table with the expected frequencies for each genotype. Enter your answers to three decimal places.

he frequencies you calculated are those you would expect if the population were in Hardy-Weinberg equilibrium. The expected frequency of genotype CGCG is p 2 = 0.484 × 0.484 = 0.234. The expected frequency of genotype CGCY is 2pq = 2 × 0.484 × 0.516 = 0.499. The expected frequency of genotype CYCY is q 2 = 0.516 × 0.516 = 0.266.

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?

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

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

metaphase I

Genetic drift is a process based on _____.

the role of chance

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

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

Using the day 7 data, what is the frequency of the CG allele (p)?

Each individual has two alleles, so the total number of alleles at day 7 is 216 × 2 = 432. To calculate the frequency of the CG allele, note that each of the 49 individuals of genotype CGCG has two CG alleles, and each of the 111 individuals of genotype CGCY has one CG allele. The 56 individuals of genotype CYCY have zero CG alleles. Thus, the frequency of the CG allele (p) is: p=(2×49)+(1×111)+(0×56)432=0.484

What is true of microevolution?

It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations. Microevolution is a generation-to-generation change in allele frequency.

A person uproots the five closest plants which all happen to have white flowers

Mechanism: genetic drift Effect on allele frequencies: frequency of purple allele increases

Fill in the table with the observed frequencies for each genotype at day 21

The observed frequency of genotype CGCG is 47÷173 = 0.272. The observed frequency of genotype CGCY is 106÷173 = 0.613. The observed frequency of genotype CYCY is 20÷173 = 0.116.

Fill in the table with the observed frequencies for each genotype at day 7

The observed frequency of genotype CGCG is 49÷216 = 0.227. The observed frequency of genotype CGCY is 111÷216 = 0.514. The observed frequency of genotype CYCY is 56÷216 = 0.259

sing the day 7 data, what is the frequency of the CY allele (q)?

You can use the same procedure that you used to calculate p to calculate q. However, an easier way to calculate q is to remember that p + q = 1. Since you know that p = 0.484, you can calculate that q = 1 - p = 0.516.

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

gene flow