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How Often Do Mutations Happen?

By Lizzette Villanueva
Last updated over 2 years ago
18 Questions
Adapted from learn.genetics.edu
Understanding Mutations
A change in the base-pair sequence of a gene is called a mutation. Most mutations occur when a cell copies its DNA for cell division. As the DNA is copied, base pairs may be added, deleted, or substituted. These chance mutations may be beneficial, neutral, or harmful to organisms.


For example, a mutation that results in longer fangs may be beneficial if it helps the bush viper seize prey. Mutations can also occur when DNA is exposed to mutagens, or substances that cause genetic mutations, such as UV radiation and toxic chemicals.
5.

What can cause mutations in DNA? Select ALL that apply.

6.

Study the original and mutated DNA sequences. Select the type of mutation that has occurred.

Deletion
Insertion
Subsitution
7.

Why is it that a insertion mutation or deletion mutation could potentially cause more damage (or a greater benefit) than the effects from a substitution mutation? Explain in 2-3 sentences.


8.

Mutations are the source of all new alleles in nature. Variations in alleles lead to variations in organisms within a population. Positive mutations lead to the organism having a better chance of survival, which means the mutation may be passed on to the offspring. Negative mutations may lead to an early death— probably before the organism can produce offspring. Therefore, changes in alleles from one generation to another form the basis of evolution.

Which types of mutations, positive, negative or neutral, are most likely to be seen in offspring several generations after the mutation occurred? Explain your reasoning in 2-3 sentences.


Calculate Mutation Rates
Organisms must copy their DNA to reproduce, and mutations can occur any time DNA is copied. Many of these mutations are corrected by cells, but sometimes a mutation is not corrected and it becomes part of the genetic code of a species.

Mutations accumulate at a fairly constant rate in the DNA of a particular species.
9.

Use the picture on the left to answer the following question.

How many mutations accumulated in this DNA sequence over 25 million years?

10.

Use the picture on the left to answer the following question.

Based on these data, estimate the mutation rate for this DNA sequence over 100 million years.

Rock Pocket Mice

Background
A mutation is a change in an organism’s DNA. Most mutations originate as copying errors. If a mutation happens in a reproductive cell (e.g., egg or sperm), it can be passed to offspring. This is a source of new alleles.

New point mutations (single-base substitutions) happen at a relatively constant rate—though the rate differs between organisms. For people, everyone has about 38 new single-base mutations that were not present in their parents. That’s one mutation for every 83 million bases—with each generation.

Because mutations happen at a consistent rate, it’s possible to predict how often a new allele of a particular gene will come along, and even how often a specific single-base mutation will happen.

Fur color in rock pocket mice
Rock pocket mice live in dry, rocky habitats in the southwestern United States and northern Mexico. Some rock pocket mice have light tan fur, and others have dark brown fur.
Scientists know that a gene called MC1R influences fur color in these mice. To have dark fur, a mouse needs just one copy of a ‘dark’ MC1R allele.
Based on genetic variations found in nature—some in rock pocket mice, some in other animals—scientists know that there are at least 10 different bases in the MC1R gene that when mutated will generate a dark fur allele.
11.

How many locations in the MC1R gene are there where a single-base mutation will make new dark-fur allele.

The figure below shows images of rock pocket mice in different environments.
12.

Which mice are most suitable to surviving in their environment? Select ALL that apply.

13.

What makes those mice you chose in the previous question suitable for survival in their environment?

Question
In a population of light-colored mice, how often will a pup be born with a new MC1R allele that gives it dark fur?


Information you will need
  • There are 20 possible bases in MC1R where mutations will cause dark fur (10 bases X 2 alleles) possible dark mutations
  • Mutation rate = 1 mutation for every 185 million (185,000,000) bases (this also means that for a single base, it will be mutated once in every 185 million offspring. )
  • The population has 5,000 female mice.
  • Female mice give birth to at least 5 pups/year.
  • 1 million = 1,000,000

Watch the video below before answering the following questions.
14.
Multiply: (mutation rate) x (number of possible dark mutations)
_______ mutation x _______ dark fur mutations = _______ dark fur mutations
_______ bases _______ mouse pups
15.
If we simplify the previous answer by dividing the numerator and denominator by 20 you get:

1 pups will have the dark fur.
[ _______ ]
16.

How many pups are born each year? (reproductive rate) Hint look at females and birth rate.

17.

Assuming the rock pocket mouse population stays the same size, how often will a pup with dark fur be born (once every how many years)? Hint: use your answers to 3 and 4.

18.

Rock pocket mice have been living in New Mexico for at least 500,000 years. In that time, about how many pups could have been born with new dark fur alleles? (Round to whole number)