Consider the age structure diagrams for counties (a) and (b). Which diagram is consistent with n

Consider the age structure diagrams for counties (a) and...

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Key Concepts

Age Structure Diagrams

These diagrams graphically represent the distribution of a population across different age groups, often separated by sex. They help demographers assess the current state and predict future changes by highlighting the proportions of young, working-age, and older individuals in a population.

Negative Population Growth Momentum

This concept refers to an intrinsic tendency for a population to decline in size over time, often indicated by an age structure with a narrow base (few young people) and a relatively larger older population. Even if the current fertility rate were at the replacement level, the existing imbalance suggests fewer births in the future and leads to overall negative growth.

Demographic Transition

The demographic transition model explains the evolution of a population from high birth and death rates to low birth and death rates as a country develops economically and socially. In the later stages of this transition, populations often experience an aging structure that contributes to negative growth momentum due to declining fertility and an increased share of older individuals.

Transcript

00:02 Okay.

00:04 So for this question, i found it best to actually have the tables up in front of me as i talked through it.

00:11 So as we can see here in population a, population, the frequency of allel a is greater than allel b.

00:21 But in population b, the frequency of allel b is greater than allel a.

00:29 However, in population b, allel a doesn't show any kind of frequency until around year three, which indicates either arising from mutation.

00:52 Because usually if it just suddenly appears out of nowhere, it's happening from a mutation.

00:57 And then as far as in population a, we can see here that the frequency of allel b is lower.

01:07 It's still pretty consistent.

01:10 It seems to be decreasing and increasing, but it's still there.

01:13 So it probably means that there's some sort of selection going on for a.

01:22 So let's see which answer option this matches.

01:25 Let's see.

01:26 In population a, genetic drift is likely occurring, causing all aloea to become more prevalent than allel b.

01:32 The population b mutation apparently occurred, introducing allel a to the population b.

01:37 Allel a also appears to be increasing due to genetic drift in population b.

01:43 Option b says in population a, natural selection is occurring with allel a being favored over allele b...

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