Question

Why is genetic drift aptly named? a. It causes allele frequencies to drift up or down randomly. b. It occurs when alleles from one population drift into another. c. It occurs when mutations drift into a genome. d. It occurs when populations drift into new habitats.

Short answer

The correct answer is (a) It causes allele frequencies to drift up or down randomly. Genetic drift is aptly named because it involves random changes in allele frequencies within a population, causing them to "drift" up or down over time.

Step-by-step solution

Understand the concept of genetic drift

Genetic drift is a random change in allele frequencies within a population. It occurs most often in small populations, and can lead to significant changes in the genetic makeup of that population. This process can cause certain alleles to become more or less common over time, even if they do not provide a direct survival advantage or disadvantage.

Analyze each answer choice

a. It causes allele frequencies to drift up or down randomly. b. It occurs when alleles from one population drift into another. c. It occurs when mutations drift into a genome. d. It occurs when populations drift into new habitats.

Choose the correct answer

The correct answer choice is (a) It causes allele frequencies to drift up or down randomly. This is because genetic drift is characterized by random changes in the population's allele frequencies over time.

Explain why the other answer choices are incorrect

b. It occurs when alleles from one population drift into another. This refers to gene flow, not genetic drift. Gene flow occurs when alleles are exchanged between populations, whereas genetic drift is a random change in allele frequencies within a population. c. It occurs when mutations drift into a genome. This is not accurate because genetic drift is not about mutations entering a genome. Instead, it refers to the random changes in allele frequencies within a population over time. d. It occurs when populations drift into new habitats. This answer choice refers to migration, not genetic drift. While migration can influence genetic diversity in populations, genetic drift refers specifically to the random changes in allele frequencies within a population.

Key concepts

Allele Frequencies

Allele frequencies refer to how common a specific allele is within a population. Think of alleles as different versions of a gene. For example, for a gene that determines eye color, there might be an allele for brown eyes and another for blue eyes. Allele frequencies indicate how often you might find each of these in a population. Changes in allele frequencies can occur due to several processes, one of which is genetic drift.
Genetic drift leads to random changes in these frequencies. Unlike natural selection, which might increase the frequency of advantageous alleles, genetic drift can cause allele frequencies to increase or decrease simply by chance. This randomness means that any allele, regardless of its effect on survival, can become more or less common in a population due to genetic drift.

Random Changes

Random changes in allele frequencies are a defining feature of genetic drift. These changes occur without any obvious external factors like environmental pressures or mutations giving certain alleles an advantage. Imagine picking a number of colored marbles from a jar, if you randomly select more red ones than green, suddenly red becomes more common in your collection, not because it is better, just by chance.
Genetic drift operates in a similar way. Over generations, random events might mean that more individuals with a specific allele reproduce, or individuals with other alleles might not reproduce at all. Slowly, these random outcomes can lead to significant shifts in what alleles turn up most frequently in a population, completely independent of the alleles' effects on the organism's survival or reproduction.

Small Populations

Genetic drift affects small populations more severely than larger ones. In small populations, each individual's genetic makeup has a larger relative impact on the population's allele frequencies compared to a large population. Thus, any random event that affects allele frequencies can have a bigger sway.
It's like flipping a coin a small number of times versus thousands of times. With fewer flips, there's a greater chance of straying from an even 50/50 distribution. Similarly, in small populations, a chance event—such as a few individuals who carry rare alleles leaving offspring or not—can shift the population's allele frequencies quickly and drastically.

• Genetic drift can lead to alleles becoming fixed: where an allele becomes the only one present within a population.
• Conversely, genetic drift can cause alleles to disappear completely.

These effects underline why genetic variability is often lower in small, isolated populations.