Biology: Genetics: Mutations and Their Effects Worksheet

Question 1

A DNA coding strand changes from ATG GAA TTT CCG to ATG GAG TTT CCG. The mRNA codons GAA and GAG both code for glutamic acid. What type of point mutation is this, and what effect would it likely have on the protein?

Accepted Answer

This is a silent mutation because the DNA sequence changed but the amino acid sequence did not change. It would likely have no effect on the protein's primary structure.

Question 2

A mutation changes the mRNA codon UAU, which codes for tyrosine, into UAA, which is a stop codon. What type of mutation is this, and why can it be serious?

Accepted Answer

This is a nonsense mutation because a codon for an amino acid was changed into a stop codon. It can be serious because translation may stop early, producing a shortened protein that may not function correctly.

Question 3

In a gene, one nucleotide is deleted near the beginning of the coding region. Explain why this kind of mutation often has a large effect on the final protein.

Accepted Answer

A deletion of one nucleotide can cause a frameshift mutation. Because codons are read in groups of three, the deletion changes the reading frame and can alter many amino acids after the mutation.

Question 4

A substitution mutation changes one codon so that the protein has leucine instead of proline at one position. What type of mutation is this, and what is one reason its effect could range from mild to severe?

Accepted Answer

This is a missense mutation because one amino acid was replaced by a different amino acid. Its effect could be mild or severe depending on whether the changed amino acid is important for the protein's shape or active site.

Question 5

A mutation occurs in a skin cell after exposure to ultraviolet light. The person later has children. Explain whether this mutation is likely to be passed to the children.

Accepted Answer

This mutation is not likely to be passed to the children because it occurred in a somatic body cell. Only mutations in germ cells, such as sperm or egg cells, can be inherited by offspring.

Question 6

A mutation occurs in a sperm cell before fertilization. The sperm forms a zygote with an egg. Explain how this mutation could affect the resulting child.

Accepted Answer

A mutation in a sperm cell can be inherited because the sperm contributes DNA to the zygote. If the zygote develops, the mutation may be present in many or all cells of the child.

Question 7

Ultraviolet radiation can cause nearby thymine bases in DNA to bond together, forming thymine dimers. Explain how this damage can lead to a mutation if it is not repaired.

Accepted Answer

Thymine dimers can distort the DNA shape and interfere with DNA copying. If the damage is not repaired before replication, DNA polymerase may insert the wrong bases or skip bases, creating a mutation.

Question 8

Some chemicals in tobacco smoke are mutagens. Define mutagen and explain why mutagens can increase the risk of cancer.

Accepted Answer

A mutagen is an agent that increases the rate of mutations in DNA. Mutagens can increase cancer risk because mutations may damage genes that control cell division, DNA repair, or cell death.

Question 9

A cell has a mutation in a tumor suppressor gene. Explain how this mutation could contribute to cancer.

Accepted Answer

A tumor suppressor gene normally helps slow cell division, repair DNA, or trigger cell death when damage is severe. If a mutation prevents it from working, damaged cells may keep dividing and form a tumor.

Question 10

A mutation causes a chromosome segment to break off and attach to a different chromosome. Identify the type of chromosomal mutation and describe one possible effect.

Accepted Answer

This is a translocation because a chromosome segment moved to a different chromosome. It may disrupt genes, change gene regulation, or create abnormal fusion genes that affect cell function.

Question 11

A chromosome loses a segment that contains several genes. Identify the type of chromosomal mutation and explain why it may have a stronger effect than a single base substitution.

Accepted Answer

This is a deletion mutation at the chromosome level. It may have a strong effect because several genes can be lost at once, which can remove important instructions needed by the cell.

Question 12

The sickle cell allele changes one amino acid in the beta-globin protein. People with two copies of the allele can have sickle cell disease, but people with one copy have some resistance to malaria. Explain how one mutation can have both harmful and beneficial effects.

Accepted Answer

A mutation's effect depends on the genotype and the environment. The sickle cell allele can be harmful when a person has two copies because it affects red blood cells, but one copy can be beneficial in areas where malaria is common.

Question 13

A mutation occurs in a noncoding regulatory region near a gene, but the protein-coding sequence of the gene does not change. Explain how the mutation could still affect the organism.

Accepted Answer

A regulatory mutation can affect when, where, or how much a gene is expressed. Even if the protein sequence stays the same, changing the amount or timing of protein production can affect traits.

Question 14

A population of bacteria is exposed to an antibiotic. A few bacteria already have a mutation that makes them resistant. Explain how natural selection can change the frequency of the resistance allele in the population.

Accepted Answer

The antibiotic kills many nonresistant bacteria, while resistant bacteria are more likely to survive and reproduce. Over generations, the resistance allele can become more common in the population.

Question 15

DNA repair enzymes fix many DNA errors before they become permanent mutations. Explain why mutations still occur even though cells have repair systems.

Accepted Answer

Mutations still occur because repair systems are not perfect. Some DNA damage or copying errors may be missed, repaired incorrectly, or happen faster than the cell can fix them.

Biology: Genetics: Mutations and Their Effects

Related Cheat Sheets

More Biology Worksheets

More Grade 9-12 Worksheets