Week 4 Chapter 19: DNA Mutations

mutagen

A chemical or physical agent that interacts with DNA and causes a mutation.

What can cause a frameshift mutation?

A nucleotide addition A nucleotide deletion

how do chemical mutagens affect humans?

Chemical agents such as nitrous acid replace Amino groups with keto groups. This disrupts normal base pairing during replication

chemical mutagens

Chemicals that cause genetic mutations

What statements about nonionizing radiation are true?

Contains low energy Includes ultraviolet light

Base excision repair

DNA repair mechanism that first excises modified bases and then replaces the entire nucleotide

order of steps during a typical DNA repair system

Detection → Removal → Replication

somatic mutations

Mutations that occur in body cells, aren't passed to offspring, and don't affect the gametes

Thymine dimers are typically caused by

UV light

germ-line mutation

a mutation occurring in gametes; passed on to offspring

A germ-line mutation is one that occurs in

a sperm or egg cell.

Examples of somatic mutations include a mutation occurring in a(n)

adult muscle cell. brain cell. embryonic kidney cell.

A mutagen is a(n)

agent that causes mutations.

During the normal course of DNA replication, the addition of a nucleotide that does not obey the AT/GC rule of base pairing creates a

base pair mismatch.

Nucleotide excision repair (NER) is the main system used in the repair of

bulky, helix distorting lesions.

Nucleotide Excision Repair (NER)

can repair thymine dimers, chemically modified bases, missing bases, and some cross-links. This process involves the removal of several bases.

nonsense mutation

change a normal codeine to a termination codon, creating a smaller polypeptide

missense mutation

change the amino acid sequence of the polypeptide

A missense mutation in the β-globin gene is responsible for sickle cell disease. This mutation causes the polypeptide sequence to

contain a substituted amino acid of the wrong type.

Silent mutations are possible because the genetic code is

degenerate.

silent mutations

do not alter the amino acid sequence of the polypeptide

True or false: It is healthy for a human to acquire new DNA mutations, because they are the driving force for adaptive evolution.

false

The addition or deletion of a number of bases that is not a multiple of 3 causes a(n) ___ mutation.

frameshift

point mutation

gene mutation in which a single (or few) base pair(s) in DNA has been changed

A mutation that occurs directly in a sperm or egg cell, or in one of their precursor cells, is referred to as a(n) ____-____ mutation.

germ line

Cells that give rise to the gametes such as eggs and sperm are called

germ line

If an individual possesses a germ-line mutation, then ______ of the gametes produced by the individual will carry the mutation. If an individual possesses a somatic mutation, then ______ of the gametes produced by the individual will carry the mutation.

half; none

A new mutation in a gene is MOST LIKELY to be ______ to the organism.

harmful

A mutant allele is best defined as an allele that

has a different DNA sequence from the wild type.

The two main mechanisms used to repair DNA double-strand breaks are ___ recombination repair and ___ end joining.

homologous; nonhomologous

frameshift mutation

involves the addition or deletion of a number of nucleotides that are not divisible by 3

Nonionizing radiation is characterized by

long wavelength and low energy.

A base substitution in DNA that ultimately leads to a change in the encoded amino acid is called a(n) ____ mutation.

missense

Sickle cell disease is caused by a

missense mutation in the β-globin gene.

A mutation in a gene that causes an amino acid change in the encoded protein is called a

missense mutation.

An agent that can change DNA structure and cause mutations is known as a(n)

mutagen

An allele that has a DNA sequence different from that of the wild type is called a(n) ___ allele.

mutant

A silent mutation is a mutation that results in

no change to the amino acid sequence of the polypeptide.

A mutation that results in a premature termination of the synthesis of a polypeptide is called a(n) ___ mutation.

nonsense

Some errors create bulky distortions of the double helix. These errors are removed primarily by a DNA repair system called NER, which stands for ___ ___ repair.

nucleotide excision

The enzyme that can recognize thymine dimers and split them is called

photolyase

A(n) ______ mutation refers to a mutation in which just one base is changed within the DNA sequence.

point

physical mutagens

radiation-x-rays, UV light

A mutation that does not change the amino acid sequence of a polypeptide is known as a(n) ____ mutation.

silent

A mutation that does not change the amino acid sequence of a polypeptide is known as a(n) mutation.

silent

Cells of the body other than germ-line cells are called ______ cells.

somatic

The patch of white hair in this child is most likely caused by a ______ mutation.

somatic

Muscle cells, nerve cells, skin cells are examples of

somatic cells.

If the patch of white hair in this child were larger, that would indicate a

somatic mutation that occurred earlier during embryonic development

Mutations in body cells that do not go on to form gametes are known as

somatic mutations

Errors in DNA replication are examples of ______ mutations, while mutations caused by ultraviolet light are ______ mutations.

spontaneous; induced

Mutations can be caused in two main ways: (1) ____ mutations are the result of natural biological or chemical processes; and (2) ____ mutations are produced by environmental agents.

spontaneous; induced

The term germ line is used to describe

the cells that produce sperm and eggs.

Translesion synthesis refers to

the replication of a template strand that contains DNA damage.

Ultraviolet light causes the formation of crosslinked ___ ___ in DNA.

thymine dimers

The synthesis of DNA over a template strand that harbors some type of DNA damage is called ___ ___

translesion synthesis

True or false: Most DNA repair systems involve three major steps: detection of the error, removal of the abnormality, and its replacement with normal DNA.

true

The wild type genotype or phenotype is the one that is

typically found in nature.

In a natural population, a ___-___ genotype is the most common one.

wild type

how do changes in chromosome structure affect gene expression?

Changes in chromosome structure may lead to a breakpoint in the DNA that Interrupts a genes coding sequence Chromosomal rearrangements ( translocations, inversions) May influence the phenotype when the rearrangement moves the gene to a new location. This is called position effect.

Double-strand breaks are typically repaired by which of the following?

Nonhomologous end joining Homologous recombination repair

What type of mutations involve a change from a normal codon to a stop codon?

Nonsense mutations

how do physical mutagens affect humans?

Physical agents, such as radiation, can change DNA molecules.

What is responsible for silent mutations?

The degeneracy of the genetic code