High School Biology : Genetics Principles

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding Codominance And Incomplete Dominance

A sugar flower has white petals, and is homozygous for this trait. Another sugar flower is homozygous for red petals. The white and red sugar flowers are crossed, and produce offspring with pink petals. Which of the following terms describes this type of inheritance?

Possible Answers:

Polygenic inheritance

Codominance

Incomplete dominance

Complete dominance

Epistasis

Correct answer:

Incomplete dominance

Explanation:

Incomplete dominance is described by a phenotype that is not completely dominant over another. Therefore, it will be a "blending" of colors in the case of this question, therefore the petals are pink. Codominance is when both dominant traits are expressed, therefore if white was considered dominant and red was also a dominant trait, the petals would have spots of white and red, with no pink. Polygenic inheritance is described by one characteristic influenced by multiple genes, which is not the case in this problem. Finally, epistasis involves the suppression of genes, however in this problem color is not suppressed.

Example Question #1 : Hardy Weinberg Equilibrium

Which of the following is NOT a requirement for Hardy-Weinberg equilibrium?

Possible Answers:

Mating must be random in nature

The population must be at carrying capacity

Organisms entering or leaving the population must not change the gene pool frequencies

The population must have a large number of organisms

Correct answer:

The population must be at carrying capacity

Explanation:

Hardy-Weinberg equilibrium has a set of conditions that must be met in order for the population to have unchanging gene pool frequencies. There must be random mating, no mutation, no migration, no natural selection, and a large sample size.

It is not necessary for the population to be at carrying capacity. The population can grow or shrink while maintaining the gene pool.

Example Question #1 : Understanding Hardy Weinberg Conditions

A species of bird has an allele for black feathers and an allele for blue feathers. Which of the following scenarios would violate the necessary conditions for Hardy-Weinberg equilibrium in a population of this species?

Possible Answers:

Predators do not discriminate between members of the species with different colored feathers

The population is isolated on an island, and new birds are unable to fly to the island

Birds with black feathers prefer to mate with birds that have similarly colored feathers

There is a large population of birds on an island

Correct answer:

Birds with black feathers prefer to mate with birds that have similarly colored feathers

Explanation:

If a population is in Hardy-Weinberg equilibrium, there is no evolution taking place in the population. One of the violations of Hardy-Weinberg equilibrium is selective mating. If birds prefer to mate with others that are similarly colored, then Hardy-Weinberg equilibrium is violated and the gene pool in the population is changing.

Hardy-Weinberg requires no migration, random mating, large population size, no natural selection, and no mutation.

Example Question #1 : Understanding Hardy Weinberg Conditions

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

Possible Answers:

Gene flow

Small population size

Nonrandom mating

Mutation

Differentiation

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 #1 : 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:

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

The population size is large

Random mating

No immigration or emigration 

No spontaneous mutations

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 #81 : Genetics And Evolution

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:

gene flow

mutation

migration

genetic drift

natural selection

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 #1 : Hardy Weinberg Equilibrium

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

Possible Answers:

A researcher randomly dividing fruit flies into mating groups

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

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

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

Mutation-free DNA replication

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 #2 : Understanding Hardy Weinberg Conditions

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

Possible Answers:

Random mating

Natural selection

Closed system

Large population 

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:

Constant fluctuation in genotypic frequencies 

Elimination of homozygote individuals 

Elimination of heterozygote individuals 

No change in genotypic frequencies 

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.

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