Interpret Trait Graphs - Middle School Life Science

What does the x-axis usually represent on a graph of population trait change over time?

Time (generations or years). Time is the independent variable when tracking changes.
What is the term for the proportion of individuals with a trait in a population?

Trait frequency. Measures how common a trait is relative to the whole population.
What does it mean if a trait becomes fixed on a graph (frequency reaches $1.00$ )?

All individuals carry that allele/trait version. Fixed means $100\%$ frequency in population.
What does it mean if an allele is lost on a graph (frequency reaches $0.00$ )?

That allele is no longer in the population. Lost means $0\%$ frequency, extinct from population.
Identify the selection type if a graph shows the mean trait value staying similar but variation shrinking.

Stabilizing selection. Narrowing distribution with same mean.
Identify the selection type if a graph shows two peaks forming over time from one original peak.

Disruptive selection. One peak splits into two distinct peaks.
What is the term for a change in trait frequencies in a population across generations?

Evolution. Heritable traits change in frequency over successive generations.
What is the percent frequency if an allele frequency is $0.65$ on a graph?

$65\%$ . Multiply by $100$ to convert to percent.
What does a flat line for trait frequency over many generations most directly indicate?

No net change in trait frequency (stable). Flat line means the trait isn't changing.
Which term describes a trait change where the middle increases and both extremes decrease over time?

Stabilizing selection. Selection favors intermediate values.
Find the change in frequency: a trait is $0.20$ at Gen 1 and $0.35$ at Gen 6.

Increase of $0.15$ . Subtract initial from final frequency: $0.35 - 0.20 = 0.15$ .
What does a rightward shift of a bell-shaped trait distribution over generations indicate?

The mean trait value increased. Rightward shift means higher average values.
What does the y-axis usually represent on a graph showing a trait changing in a population?

Trait frequency or average trait value. Shows how common a trait is or its average value.
What does it suggest if a trait frequency changes rapidly right after an environmental change on a timeline?

New selective pressure is acting. Environmental change drives selection.
What is the change in frequency if a trait rises from $0.20$ to $0.50$ over the time shown?

$0.30$ . Change = final - initial = $0.50 - 0.20$ .
Identify the trait with the greatest increase: A goes from $10\%$ to $40\%$ , B from $30\%$ to $50\%$ .

Trait A (increase of $30\%$ ). Compare absolute changes: A increased by $30\%$ points vs B's $20\%$ .
What does an increase in allele frequency over time on a graph indicate about that allele?

It is becoming more common in the population. Higher frequency means more individuals carry it.
What is the allele frequency if $30$ of $100$ alleles in a sample are allele A?

$0.30$ . Frequency = count/total = $30/100$ .
Identify the best interpretation when a beneficial trait increases after an environmental change.

Natural selection favored that trait in the new environment. The trait provides survival or reproductive advantage.
What does a graph showing cyclical ups and downs in a trait frequency over time most likely indicate?

Changing conditions or frequency-dependent selection. Fluctuating selection pressures cause cycles.
Which interpretation is correct if a model shows survivors have a trait value closer to one extreme?

Selection favored that extreme trait value. Survivors show which traits were advantageous.
What does it indicate if two trait lines cross, where trait A decreases as trait B increases?

The population is shifting from trait A to trait B. One trait replaces another over time.
Identify the correct conclusion if a model shows higher survival for one trait and its frequency increases.

That trait has higher fitness in that environment. Better survival leads to increased frequency over generations.
What does a flat (horizontal) trait frequency line over time indicate?

The trait frequency is not changing over time. The trait proportion remains constant across generations.
What is the average rate of change per generation if frequency goes from $0.10$ to $0.30$ in $4$ generations?

$0.05$ per generation. Rate = change/time = $(0.30-0.10)/4$ .
What does it mean if a trait frequency line slopes downward over time?

The trait is becoming less common in the population. Fewer individuals have the trait each generation.
Which term describes a trait change where the population mean shifts toward one extreme over time?

Directional selection. Population shifts toward one extreme value.
Identify the best interpretation when a harmful trait decreases steadily over many generations.

Selection acted against that trait. Individuals with the trait had lower survival or reproduction.
What does it mean if a trait frequency line slopes upward over time?

The trait is becoming more common in the population. More individuals inherit or develop the trait each generation.
Which option best explains a new trait appearing, then slowly increasing over generations?

A mutation arose and was favored by selection. New genetic variation can spread if it provides an advantage.
What does the y-axis usually represent in a graph of trait frequency over time?

Trait frequency (often percent or proportion) in the population. Shows what proportion of the population has the trait at each time point.
Which term describes a trait change where both extremes increase and the middle decreases over time?

Disruptive selection. Selection against intermediate values.
What does the x-axis usually represent in a graph showing population trait changes?

Time (generations, years, or breeding seasons). Tracks how traits change across multiple reproductive cycles.

Study these flashcards