High School Biology : Genetics and Evolution

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #81 : Genetics And Evolution

Which of the following is not one of the major causes of evolutionary change as outlined by Hardy-Weinberg equilibrium?

Possible Answers:

Nonrandom mating

Gene flow

Small population size

Differentiation

Mutation

Correct answer:

Differentiation

Explanation:

The Hardy-Weinberg principle is a mathematical model proposing that, under certain conditions, the allele frequencies and genotype frequencies in a sexually reporoducing population will remain constant over generations. For this principle to hold true, evolution must essentially be stopped. The conditions to maintain the Hardy-Weinberg equilibrium are: no mutation, no gene flow, large population size, random mating, and no natural selection.

The Hardy-Weinberg equilibrium can be disrupted by deviations from any of its five main underlying conditions. Therefore mutation, gene flow, small population, nonrandom mating, and natural selection will disrupt the equilibrium.

Differentiation is the process whereby relatively unspecialized cells become specialized into particular tissue types. This is a standard process in organismal development, and is generally unrelated to evolutionary principles.

Example Question #4 : Understanding Hardy Weinberg Conditions

Which of the following is NOT one of the assumptions made by Hardy and Weinberg regarding Hardy-Weinberg equilibrium?

Possible Answers:

No spontaneous mutations

All of these are assumptions made by Hardy and Weinberg in their equilibrium model.

No immigration or emigration 

The population size is large

Random mating

Correct answer:

All of these are assumptions made by Hardy and Weinberg in their equilibrium model.

Explanation:

All of the answer choices are assumptions made when considering Hardy-Weinberg equilibrium. Thus, the model is not very realistic in nature, since these conditions are rarely met. Also, no natural selection is assumed to occur.

Example Question #3 : Understanding Hardy Weinberg Conditions

A lake contains a population of twelve bluegill fish, 8 with red spots and 4 with no red spots. The fish are healthy and strong, all exactly the same except for the coloring. Fishermen visit the lake, and catch 7 fish with red spots and 1 fish with no red spots, leaving 1 with red spots and 3 without red spots remaining in the lake. This change in the population is an example of __________.

Possible Answers:

genetic drift

gene flow

migration

natural selection

mutation

Correct answer:

genetic drift

Explanation:

All the factors listed are factors that can change the genetic equilibrium of a population. Genetic drift is a random change in the frequency of alleles, as in this question—at first, there were more red-spotted fish than spotless fish (a 2:1 ratio), but once the random fishing took place, there were fewer red-spotted fish than spotless fish (a 1:3 ratio). This selection by chance is genetic drift.

Gene flow is the movement of alleles into or out of a population, generally due to patterns of migration.

Migration is the physical departure or arrival of organisms between different populations or geographical locations.

Natural selection is the increased prevalence of "favorable" traits and genes, and the decline in prevalence of "unfavorable" traits and genes.

Mutation is a genetic alteration that results in a new DNA sequence. Mutation is responsible for the creation of new alleles, traits, and phenotypes.

Example Question #2 : Understanding Hardy Weinberg Conditions

Which of the following is not an application of the assumptions underlying Hardy-Weinberg equilibrium?

Possible Answers:

Two populations of island rabbits, separated by 5 miles of ocean

A population of 2,000,000 mosquitos flying over a body of water

A male bird with large and bright feathers is more fit than other birds

Mutation-free DNA replication

A researcher randomly dividing fruit flies into mating groups

Correct answer:

A male bird with large and bright feathers is more fit than other birds

Explanation:

For Hardy-Weinberg equilibrium to be in effect, five conditions must be met:

1. Large Population

2. Isolated populations (no immigration or emigration)

3. No spontaneous mutations

4. Mating is random

5. No natural selection

Example Question #3 : Hardy Weinberg Equilibrium

Which of these factors would not contribute to Hardy-Weinberg equilibrium?

Possible Answers:

Closed system

Large population 

Natural selection

Random mating

Correct answer:

Natural selection

Explanation:

Hardy-Weinberg equilibrium describes no change in genotypic frequencies over multiple generations. This is not likely to be seen in nature due to multiple factors, but it can be a useful theory for scientists. Hardy-Weinberg equilibrium requires no immigration or emigration, a large population, random mating, and no spontaneous mutations (all of which are virtually unavoidable in nature). Natural selection would violate these conditions.

Example Question #1 : Understanding Hardy Weinberg Conditions

If all Hardy-Weinberg conditions are met, what will be the result? 

Possible Answers:

No change in genotypic frequencies 

Constant fluctuation in genotypic frequencies 

Elimination of heterozygote individuals 

Elimination of homozygote individuals 

Correct answer:

No change in genotypic frequencies 

Explanation:

Hardy-Weinberg equilibrium describes no change in the genotypic frequencies of a population. After one generation, assuming random mating, a closed system, a large population, and no random mutations, the genotypic frequencies of the population will not change.     

Example Question #1 : Understanding Hardy Weinberg Calculations

Consider a population in Hardy-Weinberg equilibrium. A gene in the population has two alleles. The gene pool shows a distribution of 80% of the dominant allele and 20% the recessive allele.

What percentage of the population is heterozygous for the trait?

Possible Answers:

Correct answer:

Explanation:

Since the population is in Hardy-Weinberg equilibrium, we can use the following equation to determine the genotypic frequencies for the allele in question:

In this equation,  represents the frequency of the dominant allele and  represents the frequency of the recessive allele. The  portion of the expression represents the frequency of heterozygotes in the population. Using the allelic frequencies given in the question, we can calculate the percentage of heterozygous individuals.

32% of the population is heterozygous for the trait.

Example Question #51 : Genetics Principles

In an isolated population of ants in the Amazon rainforest, color is determined by a single gene. Ants that are homozygous dominant (BB) and heterozygous (Bb) for this gene are black, but ants that are homozygous recessive (bb) for this gene are brown. 

If the phenotype frequencies are 0.75 black and 0.25 brown, what are the allele frequencies within this population?

Possible Answers:

Correct answer:

Explanation:

We can use the Hardy-Weinberg equations to solve this question:

We know that the black allele (B) is dominant and the brown allele (b) is recessive.

Using these two equations, we know that 0.25 are homozygous recessive (brown). This value will be equal to .

We can then solve as follows:

Therefore, we know that the frequency of each allele is equal to 0.5.

Example Question #1 : Understanding Hardy Weinberg Calculations

In a population of rabbits, the dominant B allele produces brown fur and the recessive b allele produces white fur. There are 544 brown rabbits and 306 white rabbits in the population. 

How many of the brown rabbits would you expect to be homozygous dominant (BB)? 

Possible Answers:

Cannot be determined from the information given

Correct answer:

Explanation:

In the Hardy-Weinberg equation, the value of the term  is the percentage of homozygous dominant (BB) individuals in a population. Thus, to answer this question we will need to solve for .

With the information we are given, we can calculate , which is the percentage of the population that is homozygous recessive (bb). We know the total number of homozygous recessive rabbits (306 white rabbits) and the total number of rabbits in the population (306 + 544 = 850). We can thus divide the number of white rabbits by the population total to find :

36% of the population is homozygous recessive. We then take the square root of  to find :

This value tells us that 60% of all the alleles in the population are recessive (b).  

The Hardy-Weinberg equation is based off the idea that the total number of alleles in a population is the sum of the dominant and recessive alleles, as shown by this equation:

We can use this equation to solve for  using :

This value tells us that 40% of all the alleles in the population are dominant (B).

We can now square  to obtain . Recall that this will be the frequency of homozygous dominant individuals in the population:

The result is 16%, meaning 16% of the rabbits in the population are homozygous dominant. We can then multiply 16% by the total population to find the number of rabbits who are homozygous dominant:

Thus, 136 homozygous dominant rabbits would be expected in this population.

Example Question #11 : Hardy Weinberg Equilibrium

A population of frogs, which is at equilibrium, carries a dominant allele for black spots (B) and a recessive allele for no spots (b). 76 frogs have no spots, and 399 frogs have black spots.

How many of the frogs are heterozygous (Bb) for the black spot trait?

Possible Answers:

Correct answer:

Explanation:

In the Hardy-Weinberg equation, the value of the term  is the percentage of heterozygous (Bb) individuals in a population. Thus, to answer this question we will need to solve for .

With the information we are given, we can calculate , which is the percentage of the population that is homozygous recessive (bb). We know the total number of homozygous recessive rabbits (76 without spots) and the total number of rabbits in the population (76+ 399= 475). We can thus divide the number of frogs without spots by the population total to find :

16% of the population is homozygous recessive. We then take the square root of  to find :

This value tells us that 40% of all the alleles in the population are recessive (b).  

The Hardy-Weinberg equation is based off the idea that the total number of alleles in a population is the sum of the dominant and recessive alleles, as shown by this equation:

We can use this equation to solve for  using :

This value tells us that 60% of all the alleles in the population are dominant (B).

Now that we have  and , we can calculate . Recall that this will be the frequency of heterozygous individuals in the population:

The result is 48%, meaning 48% of the frogs in the population are heterozygous.  We can then multiply 48% by the total population to find the number of frogs who are heterozygous::

Thus, 228 heterozygous frogs would be expected in this population.

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